Looking for some help and hope maybe this thread will help others in the future. I have repaired a Zenith 25MC33 chassis to working condition. I would like to go through the exercise of alignment, or at lease the motions to see where it is at. I understand care is needed and there is risk of making things worse. With that out of the way I have the SAMS folder and the Zenith CM-106 service manual, also the B&K 415 instruction Manual.

I am trying to start with IF and Trap alignment but immediately am stuck. Probably a simple setup mistake but so far I get no measurable signal on the oscilloscope. Making changes to the B&K 415 has no affect.

Per the instructions here is what I have done:

Grounded the 3 test points
Nothing is connected to the tuner and set it in-between channel 3 & 4.
Feeding signal from the B&K 415 via the direct probe to test point G
I have tried with and without the resistor/capacitor assembly as per the Zenith directions
Note this is the only connection from the B&K 415 as I have highlighted in yellow below
I tested the B&K 415 cable end to end and it measures approx. 10K resistance on both the ground and signal clips
Oscilloscope is connected to test point C1


The last pic is measuring at test point C1 while operation normally with a cross hatch video signal.


B&K 415 Setup
https://i.imgur.com/PhKqyaV.png
https://i.imgur.com/satrn4B.jpg
https://i.imgur.com/M0HJv6t.jpg
https://i.imgur.com/m2GLw8L.jpg

Zenith CM-106 Directions
https://i.imgur.com/nloPks0.jpg
https://i.imgur.com/WeqeMqk.jpg
https://i.imgur.com/8IxiLHV.jpg

Scope:
https://i.imgur.com/1EAmtII.jpg

Hard to tell, but maybe you have the scope sweep set way too fast? The sweep generator should be sweeping about 60 times per second, so the scope sweep should be around 1 or 2 msec/div. Best is not to use the internal horizontal sweep of the scope, but set up for X-Y operation, with the "too scope horizontal input" of the sweep generator for X.

old_tv_nut, thanks for the quick reply and suggestion. This leads to more questions. My apologies for the very basic questions, I am in completely uncharted territory.

Next step try connecting the B&K 415 output labeled "To Scope Horz Input" to the Oscilloscope "CH1 or X"
I assume I can connect the scope probe to the B&K 415 cable as shown below, note this measures as a simple straight through cable
I currently have just a single 10x scope probe, model 4904-2RA, specs here: https://store-9x7452d.mybigcommerce.com/content/4900%20Basic%20Kit%20Technical%20Data%20Sheet.pdf
I assume I need a second scope probe to connect "CH2 or Y" to the TV chassis test point C1
Looking at the B&K 415 connection diagram it also shows connecting the "To Scope Vert Input", when would this be used, I would think this connects to the scope "CH2 or Y" input, this is confusing, don't I need to be measuring TV chassis signals?


https://i.imgur.com/PhKqyaV.png
https://i.imgur.com/OukZvrw.png

Watching Shango work on TV alignment with a B&K 415 and it looks like he has the "To Scope Horz Input" connected to the A Trigger scope input via a simple dual banana to bnc connector. Video here: https://www.youtube.com/watch?v=CmEyYAjjsn0&t=992s. Here is maybe a connector adaptor I could use: https://www.pasternack.com/banana-jack-bnc-male-straight-adapter-pe9011-p.aspx

I'm still not sure when I would then also use the "To Scope Vert Input" coming out of the B&K 415.

First what ever you do is FLAG you alignment tool with a piece
of tape so you can go back to the start !!!! Write down the turns
CW or CCW as you go. It shouldnt take much, like <1/2 turn.
Traps can be adj with an OTA signal ( 41.25, 4.5 etc)

Now the dirty truth. I was in the TV biz from 1970 til the end of CRT's
I never did an alignment. Only one tech I knew in the area did one
just to say he did. I may have seen ten sets ever that needed it.
A few had a damaged transformer & got eye balled. A few more
got tweaked but not by a tech. A few others were real Emersons
built in the mid - late 60's. Total toilet sets !

good luck
Zeno:smoke:
LFOD !

You do not need any scope probes, but you do need cables with connectors that fit the B&K

The way the B&K works is as shown in its diagram.
Instead of connecting a scope probe to the TV detector test point, you connect the B&K direct probe to the TV detector point. The B&K then adds the frequency markers to that waveform and outputs the combination of sweep waveform and markers to the B&K connector labeled "To Scope vertical input." Connect this to the scope Y input
Connect the B&K connector labeled "To Scope Horizontal Input" to the scope X input.

The alignment procedure you posted assumes that you have separate sweep and marker generators, but with the B&K they are combined internally and you do not need the resistor and capacitor assembly shown in figure 6, and do not need to connect the scope directly to the TV.

In one sentence, the TV is connected only to the B&K, and the scope also is connected only to the B&K.

Another tip: Set both the X and Y scope inputs to DC. If set to AC, the waveform will likely be distorted because it is only at 60 Hz or so, and you will royally screw up the alignment trying to compensate for the phony waveform.

I changed the scope connectors on the front panel of my B&K over to BNC connectors (it literally was unsolder the center pin, unbolt old connector, bolt in new connector, and resolder center wire) so I can connect it to the scope with simple common cables with BNC at both ends...Works like a charm with the scope in XY mode. Have only tried one alignment so far.

Thanks everyone for the help so far. I now have the scope connected in X Y mode direct to the B&K 415 and get a signal, see the below image. Further I have the direct probe connecting the B&K 415 to the Video detector (test point C1). The issue now is I get no feedback from the TV, whether connected to the TV or not I get the same curve on the scope.

Do I still use the Zenith service manual directions? I did try to connect the RF-IF-Video output and feed it into test point G as per the service manual but no change.

Could something be wrong with the B&K 415?

https://i.imgur.com/nLC9zRm.jpg

Very curious.
That does not look like an X-Y mode display. What it looks like is possibly the signal that should be going to the X axis (the left to right sweep) is showing on the Y axis,while the scope is still using its internal x axis (time) sweep.

Also, do you have adjustable AGC bias connected from the B&K to the appropriate point in the receiver? The Zenith manual will tell you where to connect it.

Is the timebase (sweep) knob on the scope turned to “x y” ?
:scratch2:
jr

Watching Shango work on TV alignment with a B&K 415 and it looks like he has the "To Scope Horz Input" connected to the A Trigger scope input via a simple dual banana to bnc connector.

He is using an older scope (453?), which uses the trigger input for external horizontal input. Your newer scope uses channel 1&2 for x-y display.

jr

The problems were operator error, Jr was correct, I had never noticed the the very last time division setting was for X Y. With the scope maybe(?) now setup correct I am ready to go.

Note the first section of the scope output seems to be dead, regardless of the scope setting or the sweep settings. The first pic is while measuring the TV, the second pic is just from the B&K 415 and TV not connected:

https://i.imgur.com/XTh4xs9.jpg

https://i.imgur.com/PnxzJn0.jpg
https://i.imgur.com/yy9CJ2t.jpg


On to the alignment, step 1 - 41.25 Trap Alignment:


Set tuner in-between two channels, I also have the antenna disconnected
Ground test points B, F, E
Connect from the "Direct" output to test point C, note the direct cable has an in-line 10K resistor
Connect from the "RF-IF-Video" output to test point G and set the function to IF and the probe to 75 ohm, also note I am not using the capacitor/resistor network as described in the Zenith service manual
Connect from the "To Scope Horz Input" and "To Scope Vert Input" to the X and Y (CH1 & CH2) on the scope and set the Sec/Div to XY mode
Alignment instruction state to center frequency at 43.5 mc which is not easy to see, with all of the markers shown in the service manual turned on I set the center frequency where the full wave form was visible
Alignment instruction state to set the sweep at 6 mc, there are no markings for this, the manual states the IF range is less than 1 MHz to over 10 Mhz), I left the sweep width at max, note from about 3/4 to max there is little affect, below 3/4 and I start to loose the waveform
Alignment instruction state to adjust the bottom slug on L4 to minimize the 41.25 mc response and then to adjust the top slug on L4 to further minimize the 41.25 mc response


Turns out I don't have the the right adjustment stick, mine is either worn or undersized, a 3/32 allen wrench fits perfect which is just under 0.1", I have order a plastic adjustment stick and will report back soon. Edit: adjustments sticks arrived, no adjustment was needed for L4.

https://i.imgur.com/Ubaqqkc.png
https://i.imgur.com/8IxiLHV.jpg
https://i.imgur.com/9qGj6qi.jpg
https://i.imgur.com/GcXAxKO.jpg
https://i.imgur.com/Ng5Ef1M.jpg

Try switching ch 1 to ac and adjust position and sensitivity to get a better centering of the relevant portion of the display. :scratch2:

Don’t know, never used a B&K sweep generator.

jr

Looks like you've got it!
The offset you show with a question mark is the pulse that you saw before the sawtooth when you were accidentally not in XY mode. If needing the horizontal position set to max left is annoying, you can try switching to AC coupling on channel 1 (X). You can watch to see if the waveform shape changes. If it does, it's still OK to use it even if the *shape* doesn't look exactly like the Zenith manual. The important thing is the relative amplitude (vertical) at each marker, which will be good as long as channel 2 (Y) is DC coupled.

The Zenith manual should tell you what percent of peak each marker frequency should be.

You can also try adjusting the center frequency, as long as that doesn't clip off one end or the other (left or right) of the waveform.

Continued 41.25 Trap Alignment:

Connect from the "Direct" output to test point C2
Adjust T4 top and bottom slugs to match Figure 11, posted below
These did take a very small amount of adjustment, hopefully I make it better, see below, sorry looks like the x axis on the before pic is not the same as the after,

https://i.imgur.com/Nz6BhDU.jpg
https://i.imgur.com/SnXTXZZ.jpg

L1, L2, L3 alignment:

Grounded test points E, B, F and tuner in-between channels
Connect from the "Direct" output to test point C2
Connect from the "RF-IF-Video" output to test point A on the tuner and set the function to CH 4, I kept the probe set to 75 ohm
Directions note if needed to apply a positive voltage to test point E, I did not


The direction call to adjust for minimum response as you adjust each coil and there may be some interaction, I was not sure on how to do this as it relates to the scope response, I just tried to get the response cure to match the picture, zooming in on the scope was some help. SAMS directs making these adjustments and using a VTVM to indicate. I tried this too but not easy to adjust to the minimum, note I cheated and used test point C2 (accessible on the chassis) which is in front of R49, 330 ohm, where SAMS has test point E on pin 7 of the sound & sync amp tube.

Adjustment to L1, L2, and L3 got tricky real quick and trying to keep track of the adjustments in case I need to go back went out the window. I did find adjustments in the subsequent step helps with getting a matching response curve. I likely will repeat all of these steps as I zero in on the alignment.

https://i.imgur.com/59uepBS.jpg
https://i.imgur.com/mxldVuy.jpg
https://i.imgur.com/DDaQ2PS.png
https://i.imgur.com/3UgU1G9.jpg
https://i.imgur.com/94pxjLE.png

Starting point with the same 7 markers turned on as indicated in Fig 12, note Zenith uses a 41.75 while the B&K 415 has a 41.67, close enough :)
https://i.imgur.com/PWBjuFZ.jpg

Tuner converter plate coil & IF Transformers T1, T2, T3 alignment:

Grounded test points E, B, F and tuner in-between channels
Connect from the "Direct" output to test point C1 and later C2
Connect from the "RF-IF-Video" output to test point A on the tuner and set the function to CH 4, I kept the probe set to 75 ohm

Adjustments are described below. Question: the directions often state adjust for maximum or minimum response at the specified marker frequency, I assume I should adjust the specified coil to get the marker to fall on the pictured response curve in the correct place, but I can also adjust to simply get the highest or lowest scope response for the marker, doing this completely messes up the curve.

I will follow up with some pics of where I land for the final IF & Trap alignment.

https://i.imgur.com/BE7CErg.jpg
https://i.imgur.com/grhL3GV.jpg

... I kept the probe set to 75 ohm
[/LIST]
... I assume I should adjust the specified coil to get the marker to fall on the pictured response curve in the correct place, but I can also adjust to simply get the highest or lowest scope response for the marker, doing this completely messes up the curve.

...
https://i.imgur.com/BE7CErg.jpg
https://i.imgur.com/grhL3GV.jpg

1) Exactly what probe are you setting to 75 ohms? Is this a scope input setting?

2) What do you mean by "fall in the correct place?" If the procedure says min or max at the marker, it means only that - the vertical position of the marker should be min or max. If the curve ends up looking wrong *at the end after all adjustments have been made*, there is something wrong with your setup or you made a mistake earlier in the procedure.

It is possible the curve won't look right when you are only part way done.

The 75 ohms is the setting on the B&K 415 Signal cable, you can select 75 or 300
https://i.imgur.com/kOLPwDR.png

"fall in the correct place?" maybe not the best way to describe but as I adjust a coil the response curve on the scope moves right or left which has the effect of moving the marker up or down

Linked below is a small video of adjusting the 41.25 coil above an below what to me is the peak which I assume is the minimum response
https://imgur.com/VRn62J5
https://i.imgur.com/A86c4FU.jpg


I agree on needing to bring it all together, I will follow up with where I am at in a bit.

OK here is where I am at:

Scope measuring on test point C1, all 7 markers are turned on, note the B&K 415 has a 41.67 marker vs a 41.75 marker which is what Zenith references. Directions are to make adjustments to the 41.25, 47.25, and 39.75 traps (L1, L2, L3) for minimum responses, accuracy of trap attenuation and marker locations.

https://i.imgur.com/1s8rpFt.jpg

https://i.imgur.com/sVXHXKY.jpg

Scope measuring on test point C2, same 7 markers are turned on. Goal is to make adjustments to the converter plate coil and 1st IF coil (T1) to match the response and also to adjust the 2nd and 3rd IF coils (T2, T3) for maximum response and to approximate the response curve.

https://i.imgur.com/wpi2kKC.jpg

https://i.imgur.com/LSjbWCQ.jpg

The 75 ohms is the setting on the B&K 415 Signal cable, you can select 75 or 300
https://i.imgur.com/kOLPwDR.png

"fall in the correct place?" maybe not the best way to describe but as I adjust a coil the response curve on the scope moves right or left which has the effect of moving the marker up or down

Linked below is a small video of adjusting the 41.25 coil above an below what to me is the peak which I assume is the minimum response
https://imgur.com/VRn62J5
https://i.imgur.com/A86c4FU.jpg


I agree on needing to bring it all together, I will follow up with where I am at in a bit.

Is the vertical input of your scope set to DC? it appears it may be set to AC and the whole curve may be shifting up and down, confusing the measurement of the actual vertical position of things.

The spec for 41.25 attenuation at C1 is 24 dB or greater, which means it's Ok if it's higher on the scope (closer to the top, which equals zero signal) than shown in the illustration.

At C2: a 1 dB reduction in signal from the peak is the same as a 20% [correction - 10%] reduction. So the distance shown as 1 dB in the illustration should be 20% [correction - 10%] of the max height. (the sketch looks poorly drawn - more like 10%.) [Correction - the sketch looks correct]You are getting over 30% attenuation at the markers, so this indicates the curve is too narrow.

Please see correction to previous post - 1 dB should have been 10%, not 20%

The spec for 41.25 attenuation at C1 is 24 dB or greater, which means it's Ok if it's higher on the scope (closer to the top, which equals zero signal) than shown in the illustration.

At C2: a 1 dB reduction in signal from the peak is the same as a 20% [correction - 10%] reduction. So the distance shown as 1 dB in the illustration should be 20% [correction - 10%] of the max height. (the sketch looks poorly drawn - more like 10%.) [Correction - the sketch looks correct]You are getting over 30% attenuation at the markers, so this indicates the curve is too narrow.

old_tv_nut, thank you for the ongoing advice and help. I will follow back up hopefully with an improved alignment. Two quick items, first I transposed labeling C1 and C2 against the last pictures I posted, I wont edit my earlier post as your reply align with what I originally had labeled. Second I have Ch1 and Ch2 set to DC. Here are my scope settings, if something seem incorrect please advise:

https://i.imgur.com/K0QSL1t.jpg

I have tried to get the 43 to 44 mc at 1db (10%) of the 42.75 and 45 mc markers. I got it down to 20% but this comes at a cost of moving other markers out of proportion. Thoughts on which markers are most important to have correct? Note currently I am trying to get the curve shape to match and to keep the 42.75 and 45 mc parallel.

https://i.imgur.com/eAZK1Ah.jpg

https://i.imgur.com/EYaZH8i.jpg

Curious that the drawings show 42.75 and 45 equal for both test points, but your measurements don't. Not sure what to think about that.

OK, I went back through the whole thread from the beginning, and I see you are not using the RC network from figure 6, and have the sweep generator output termination set to 75 ohms.

Try this - keep the sweep generator output termination set to 75 ohms, but add onto it the RC network from Figure 6. My guess is that the 75 ohm impedance is loading whatever grid circuit you connect to and that is causing the incorrect responses.

I think I read too fast earlier and mistook the RC network in figure 6 for an external marker adding arrangement - apologies!

Oh! Revelation! You are using the RF cable, 75/300 ohm switchable, which should only be used for antenna input. Use a plain unterminated cable as shown in the Zenith illustrations, with the RC network of figure 6.

Oh! Revelation! You are using the RF cable, 75/300 ohm switchable, which should only be used for antenna input. Use a plain unterminated cable as shown in the Zenith illustrations, with the RC network of figure 6.

I am using the Zenith service manual directions coupled with trying to use the B&K 415 and supplied signal cable which is the RF cable with built-in 75 or 300 ohm termination. There are no other signal cables described in their manual, see below. Also the snippet below had me believing I could the supplied cables and use the manufacture's directions, the output switch does have options to output video, IF, ch4, & ch 10, but it is odd to use a RF cable to feed into a IF circuit.

https://i.imgur.com/UyxlmII.jpg
https://i.imgur.com/TgALh9P.jpg

The Zenith service manual directions for the IF alignment steps in question state to connect the sweep and marker signals to the converter control grid (Test Point A on the tuner). No reference is made to any coupling circuit, which matches your note to use a plain unterminated cable. Zenith info below:

https://i.imgur.com/53rbg0u.jpg
https://i.imgur.com/I6vNFkP.jpg

In that case, the 75 ohm setting may work when used with the Zenith RC circuit added. The 75 ohm setting may actually just be a direct feed through.

In that case, the 75 ohm setting may work when used with the Zenith RC circuit added. The 75 ohm setting may actually just be a direct feed through.

I found some info on the TP-41 cable here: https://www.youtube.com/watch?v=kRaYG-dmCPw and have drawn it below. Note when using this cable connected to the tuner mixer grid input I have the B&K 415 set to ch4 and am using the 75 ohm setting, I tried the 300 ohm setting which works and seems to provide the same curve but I have to turn down the vertical resolution to fit it on the screen. For the earlier 41.25 Trap Alignment I connected the cable to the 3rd IF grid (test point G), set to 75 ohms and the B&K 415 output set to IF.

https://i.imgur.com/0Uc9DjM.jpg

Zenith Service Manual Sweep and Marker generator circuit drawn below.

https://i.imgur.com/lYEkMiq.jpg

The directions note to use the above circuit on the first step which is 41.25 Trap Alignment, it does not mention it's use for the subsequent steps, either you don't need it or it is assumed you use for the remainder of the steps. Below is all that is said for connecting to the tuner. If the circuit is to be used the B&K 415 circuit is close, if you are not to use this circuit than the B&K 415 supplied cables are lacking as it did not come with a BNC pass through cable, which I hope means you don't need it.

https://i.imgur.com/AeKfeYk.jpg

OK, the 75 Ohm setting of the B&K termination is closest to the Zenith drawing, and has a capacitor of reasonable size in series.

At this point, I'm not sure if the difference is enough to cause a problem, but the best way to find out is to use a direct cable with the Zenith RC network and see.

Another thought: is it obvious which of the B&K clip leads is ground and which is the 750 pF? Could they be reversed?

Take a look, below are 3 scope images using different cables to feed signal into the tuner converter control grid (Test Point A). Note I had to turn down the vertical scope by one setting for the direct connection cable as the signal came in stronger. I tried to overlay all three images in photoshop, each was slightly different in horizontal or vertical size but I would have to argue the curve and marker locations and marker attenuations all look very close.

Maybe antidotal but while waiting for the set to warm up I was watching some content via the converter box and the picture to me looked better, so at least I am not making it worse.

https://i.imgur.com/5qVsJsw.jpg

I may try to further tweak the IF alignment but its maybe about as good I can do. Would there be any components that are suspect? See below for all of my in-circuit measurements, I did replace the 2 film capacitors also using NOS tubes that test very good, I guess I could swap just to see what happens.

https://i.imgur.com/h1jsX5m.png
https://i.imgur.com/DQ0OJaE.png

I don't have enough direct experience with this particular chassis to point at a particular component and say "look at that." The curves are close to
the manual except more peaked in the center, so actually may be within normal range, especially since you see differences depending on the cable.

One experiment you could try: Since A9, A10, and A11 have their tuned frequency specified on the schematic, simply tune each one back and forth a bit to see if each is really producing maximum response at the specified frequency. If they are, I would say there's no more to be done.

Here is an interesting finding, I swapped out the three IF tubes with spare tubes. No real change for the first and second IF tubes but the third IF tube (6EJ7) did yield a much different response curve, see below. Note the tubes were tested with a B&K 747 tube tester where good starts at 65 on a 0 - 120 scale.

Sylvania 6EJ7 testing at 77, this is the tube I have been using
https://i.imgur.com/TkCw8UD.jpg

Alternate tube, Zenith 6EJ7 testing at 80, note I still need let this tube run for a good amount of time, but interesting how much the tube affects the response. Also note about 1 turn on the alignment transformer and I can get the curve about correct but not as good as the first tube.
https://i.imgur.com/oWMIjpN.jpg

A thought: while each tube type tests differently the good 6EH7 tubes I have all test around 90 to 100 while the 6EJ7 tubes I have only test around 75 to 80. Again different tube type but maybe the 6EH7 tubes I have are a bit weaker.

Your tube tester may be telling you whether the tube's emission is normal or weak, but it will tell nothing about the frequency response.

What do you mean - "need to let it run a good amount of time?"

The difference in response with different tubes is way too much. It looks like the last waveform you posted is grossly mistuned, the dip at the 4th major division from the left should not be there, just a smooth slope like the next to last waveform.

From your chart it looks like you replaced the few caps that were grossly out of tolerance., so unless you made a mistake resoldering them, there's no clue there.

Do you have more 6EJ7s to try?

Could we be missing something that can't be seen in your posting, like a dirty socket? What happens if you wiggle the tube?
Is the tube shielded? Does the shield have good ground contact?

Thanks for the next round of advice, see below in red my response. I will work through the below and report back.

What do you mean - "need to let it run a good amount of time?"
I snapped the picture right after the set came on with the tube substitute, I thought maybe letting the set run for 30min might make a difference as the tube warms up.

The difference in response with different tubes is way too much. It looks like the last waveform you posted is grossly mistuned, the dip at the 4th major division from the left should not be there, just a smooth slope like the next to last waveform.
I agree this is odd, when I substituted the alternate 6EJ7 I got the large dip, I could get a smooth slope but had to adjust the coil (L6) by approx 1 turn. I would think a bad socket as you noted could be a possible culprit. I will do some investigation here.

From your chart it looks like you replaced the few caps that were grossly out of tolerance., so unless you made a mistake resoldering them, there's no clue there.
the chart I posted was what I measured with the parts in circuit, no parts in the IF section with the exception to the 2 film capacitors were replaced. Everything I read says leave the IF section alone unless you are sure they are bad. As for the out of spec parts they are ceramic capacitors and I will guess/hope that if I lift a lead and measure they will be ok too, but I may have to come back and check. C19, C20, and C21 are listed as 10% and I ,measured them at 20%, so maybe worth pulling a lead to better test
https://i.imgur.com/2HAc7ZX.png

Do you have more 6EJ7s to try?
Yes I will try some more swapping?
Could we be missing something that can't be seen in your posting, like a dirty socket? What happens if you wiggle the tube?
Is the tube shielded? Does the shield have good ground contact?
the chassis by design has no shields on the IF tubes, the chassis is also in very good clean shape, thus the tube sockets all look clean, that said I tried substituting with a 3rd 6EJ7 that I did wiggle and got the scope curve to bounce around, I will go back and check this out more closely

I didn't understand the cap readings were in-circuit. Never mind - probably all OK.

I will be intersting to see how much variation you get with multiple tubes.

The happiest result would be to find one tube is the odd one out and then you could trash that one.

Back in the day, ringing of fine detail in the luma was cured by replacing the 3rd IF/6EJ7, even though the tubes showed 'good' on the tester. Ran into this right after the 6EH7/EJ7 lineage started appearing.

Curiosity got to me so I pulled the chassis out and measured the capacitors around the 3rd IF that my earlier in-circuit testing showed way high/low. See below, what does everyone think, would tighter tolerance capacitors improve the response? C19 looks the most critical and is spot on.

C18 - .001uf 10% 1kv ceramic capacitor, measures out of circuit 1090pf which is 9% high
C19 - 100pf 10% 500v N750 temp code ceramic capacitor and measures out of circuit 99.54pf
C20 - .0015uf 10% 500v ceramic capacitor but measures out of circuit 1194pf which is 20% low (Zenith # 22-12)
C21 - .001uf 10% 1kv ceramic capacitor but measures out of circuit 785pf which is 22% low (Zenith #22-17)


If I do look to replace C20 & C21 they look to be a generic temp code, searching for the SAMS replacements part numbers returns a temps code of X5F

https://i.imgur.com/2HAc7ZX.png

All those .001 caps are just bypasses, so value is not critical unless lower than spec'd tolerance.
.0015 is also a bypass, but I would replace it since it's out of 10% tolerance. Note that a larger value with a wider tolerance could have been spec'd here but probably was not because the next widely available larger value would have been more expensive even with the wider tolerance.

The 100 pF is a tuning cap, so should be within spec (as it is). Correction: hard to say the 100 pF is the main tuning, but it may affect it.

More thoughts:
1) I just re-read C21 is low - replace it.
2) the input capacitance of V3 may be affecting things
3) I hope you don't have anything connected to point D while alighning the IF

I will plan to replace C20 and C21 with the below parts from DigiKey which have a temp code of XF5 and align with what SAMS specifies for replacements:

https://www.digikey.com/en/products/detail/vishay-cera-mite/562R10TSD15/2825257
https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/562R10TSD10/2345250


As for the SAMS test point D, that correlates to the Zenith Service Manual test point G. This test point is only used to feed the signal generator in as part of 41.25 trap alignment, for the remining IF alignment steps this test point is unused with nothing connecting to it. Before I order I will double check parts in the IF circuit. I also gambled and purchased on Ebay two claimed NOS 6EJ7 tubes. Thank you, Brad.

Time for an update. I replaced C16, C20, and C21 which all measured 20+% low. I also spent some time swapping tube and seem to have found the right mix, note I did have a poor performing 6EJ7 tube. I might be getting closer, thoughts on what to try next?

Does one of the 2 below attempts look ok?
Are there components I should go back and check?
It's possible a fresh attempt might yield 100% success.
I can try again and maybe find a happy middle ground?


Attempt 1
After going through all of the IF alignment steps I was able get the markers and attenuation to match the Service Manual overall response curve at test point C2. But when going back and remeasuring at test point C1 the 41.25mc marker is not at minimum and the response in-between the 39.75mc and 41.25mc markers seems large, not sure if this is concerning. See the image below:

https://i.imgur.com/8UXuUT8.jpg

Attempt 2
Next I went back to test point C1 and found adjusting the 41.25mc trap was my best option to minimize the 41.25mc response while not messing up the overall response to bad, note the response in between the 39.75 and 41.25 mc markers is still large. Going back to test point C2 shows the 41.25 marker is not correct. See below:

https://i.imgur.com/FcXuzga.jpg

For reference here is the SAMS IF circuit schematic with the Zenith Service Manual test points and coil/transformer part numbers. Also here are the abbreviated alignment steps:

L4 41.25mc (Bottom Tuned) - set to minimum response
L4 41.25mc (Top Null) - set to minimum response
Directions say not to go back and adjust L4 (this is what I did to get the option 1 response curve, the response curve in option 2 is closer to correct, but that means other adjustments are needed)
T4 Primary & Secondary - adjust to match response curve
L1 41.25mc - set to minimum response
L2 47.25mc (Bottom Null) - set to minimum response
L2 47.25mc (Top Tuned) - adjust to 47.25mc (some interaction may exist)
L3 39.75mc - set to minimum response
Recheck L1, L2, L3
T1 45.75mc - adjust to match response curve
T2 45mc - set to maximum response
T3 43mc - set to maximum response
Recheck to ensure marker locations and attenuations


https://i.imgur.com/R9kqx9u.jpg

Attempt 1 looks better than atempt 2, except - is it possible you have swapped C1 and C2? The scope response to the right of the Figure 12 C2 drawing looks like a reasonable video response.

The scope picture to the right of the Figure 13 C1 drawing has a peak at the sound subcarrier, 41.25, which it seems might make sense to feed the Sound-Sync amp, although the drawing doesn't show such a huge peak.

Did you replace any capacitors in the sound-sync detector area? Particularly note C22 is a very small value, 0.82 pF.

IF capacitors that could be in question:

C22 and C23 are original and untouched
C18, C19, C24 previously measured good after lifting a lead
C13, C14 replaced film capacitors, re-measured good in circuit 12/27
C16, C20, C21 all measured 20% low, replaced today and measured good in circuit 12/27
No other IF capacitors replaced


Doubled checked C1 and C2 test points on underside, all is correct

Maybe an issue: I retested R52 which is a 5% (gold band) 180 ohm that in and out of circuit measures 219 which is 22% high. I will replace, note I only have metal film resistors which some argue against using in the IF circuit.

R52 looks like it could affect the width of the 41.25 trap.

Looking at your two attempts again, I don't quite understand how readjusting L4 doesn't minimize the 41.25 response at both C1 and C2 simultaneously, resulting in the desired curves, but obviously it's not doing that, and is making one or the other worse.
So, I'm puzzled and waiting to see the result of replacing R52.

For the alignment directions I have been using the Zenith CM-106 Service Manual which covers the 25MC33 chassis, nearly identical is the CM-105 Manual which covers just the 25MC30 chassis, but there are a few small changes.

Alignment for T4 is slightly different, maybe...
https://i.imgur.com/33leKSj.png

https://i.imgur.com/0Fpe1U3.png

I just measured the output at test Point C2 and I believe I was overdriving the signal from the B&K 415, reducing the signal does have an affect on the response, I now have it set to exactly 2 volts via my DMM from Test Point C2 to ground.
I was hesitant to make any adjustments on the tuner but with the above detail I rocked the converter plate coil on the tuner and believe the adjustment may help.



My chassis is a 25MC33, note SAMS lists both chassis under the one folder. These two chassis are very similar with only minor circuit changes I could see in the schematic. Interestingly the IF section on my chassis is wired like a 25MC30.

C15B on the 25MC30 is a 0.001uf vs a 470pf to ground on the 25MC33
C17B on the 25MC30 is a 0.001uf vs a 470pf to ground on the 25MC33
An added 100pf capacitor is present from Pin 6 to Pin 8 on the sound sync amp tube for the 25MC33


https://i.imgur.com/ivXhv1j.png

Aha! These curves do show a peak between 41.25 and 41.75 at C2. It also looks pretty obvious that you swapped the C1 and C2 sweep traces in your previous posts.

Based on what you just posted, I would say the "attempt 1" traces look correct or very close.

I am getting closer. I now am ensuring the sound detector (C2) voltage is at 2 volts and the video detector (C1) is at 6 volts. Over/under driving these voltages does affect the signal response. I also labeled the scope each time I snapped a picture so not to mix them up (label includes signal generator input and scope output). See below for where I am at:

The one concern I have is on the sound detector C2 response curve there is no real response dip like shown, my curve just starts to slope down continuously until it gets to the 41.75mc marker. Is it possible that I am still way off and need to push the 41.25, 41.75, and 42.75 further right on the wave form, that would put the 41.25 on the top of the first peak but currently is at 25% vs the spec of less than 5%.

https://i.imgur.com/3L7yKuK.jpg

https://i.imgur.com/rfD4r4p.jpg

https://i.imgur.com/Ty8ZWCr.jpg

https://i.imgur.com/ps4OXEv.jpg

Out of curiosity I adjusted L1 (41.25mc trap) and L3 (39.75 trap) to their max and I was able to get the below curve, all other coils and transformers I left as-is. It seems like if I had a bit more adjustment in the coils I could get the response curve to dip between the 39.75mc and 41.25mc markers. Also not sure then why such a response around the 41.75mc marker, while the drawing shows a bit of a curve here my set exaggerates the response around this marker.

Would there be a particular capacitor in these trap circuits I should look at? All of these capacitors are precision low values that are not easy to measure, I would have to remove the capacitors and either try to measure or just replace.

I also could just move on. Maybe unrelated but after going through the power supply, horizontal and vertical circuits there was low sound and serious buzzing/noise in the sound circuit, the Quadrature, Intercarrier, and Sound Take Off coil all needed a good bit of adjustment. I still get buzzing/noise during screen changes such as when going to commercials.

https://i.imgur.com/Af39TQY.jpg

"I am getting closer. I now am ensuring the video detector (C2) voltage is at 2 volts and the sound detector (C1) is at 6 volts. "

I think you mean "sound detector C2 and video detector C1" ?

"I am getting closer. I now am ensuring the video detector (C2) voltage is at 2 volts and the sound detector (C1) is at 6 volts. "

I think you mean "sound detector C2 and video detector C1" ?

Yes, you are correct, I will fix my typo.

"Out of curiosity I adjusted L1 (41.25mc trap) and L3 (39.75 trap) to their max and I was able to get the below curve, all other coils and transformers I left as-is. It seems like if I had a bit more adjustment in the coils I could get the response curve to dip between the 39.75mc and 41.25mc markers."

When you say dip do you mean lower on the scope screen (actually an increase in signal)? Matching that blip is not important. What is important is that the response at
42.75 and 45.0 are equal, 45.75 is at 50%, 39.75 is practically zero (high on the scope trace) and 41.24 is high on the trace, at -24 dB or greater, which means less than 6% of the peak response.

Also, 45.75 should be at 25 or 30% per the drawing, not 15% as in your last trace.

Correction: I meant 41.75, whihc I was reminded by later post is actually 41.67 in the B&K.

I think I got it. Note the B&K 415 outputs a 41.67mc vs 41.75mc marker. I maybe could try to reduce the 47.25mc marker as it is not quite at zero. The peak to peak signals at each test point is still an interesting element as changing the amount of signal from the B&k 415 going into the tuner does change the response curves. I might try to measure the tv when it is normally running to see what I get.

C1
https://i.imgur.com/Yi3MCP2.jpg

C2
https://i.imgur.com/s7ccnzw.jpg

I think this looks excellent.

Next up: Sound and 4.5mc trap, these went well. See below for directions:

Sound

Tune in a station, note I used a DVD player that I could pause and then turn up the volume to hear the noise
Added an attenuator in-line with the converter box and tuner, set to 20db attenuation
Adjust the quadrature coil, intercarrier coil, sound take off coil and buzz potentiometer to minimize hum/buzz/hiss


4.5 Trap

Tune in a station
Color switch on
Ground test point K
Connect the standard oscilloscope probe to test point K
De-tune slightly with the fine tuning, when doing this I could see the below line on the scope fatten
Adjust L7 to minimize the 920kc beat
https://i.imgur.com/zZHdg3c.jpg


Chassis test point and component locations:
https://i.imgur.com/aWwl92O.png

https://i.imgur.com/oKXWk2O.png

Moving right along to the Color Amplifier alignment, below are the steps I took. Also posted are the Zenith Service manual and SAMS directions.

Disconnect the tuner antenna input and set tuner in between channels
Color switch on, color level set to the halfway point
SAMS directions say to set the hue to the halfway point so I did this too
Ground test point K
Connect -6 volt bias to test point Q
Connect the oscilloscope to the B&K 415 via the Horz and Vert inputs
Connect demodulator probe (PR-151) from the B&K 425 Demod connector to test point U which is the cathode of the R-Y demodulator tube
B&K 415 output set to Chroma, function set to Video
Connect the B&K 415 signal to test point C1, I used the supplied RF Cable probe (TP-41) set to 75 ohms
Set the sweep center frequency to 3.6mc, I kept the sweep width at max
Note the B&K 415 does not have a 3.63mc marker


Here is my starting point, mostly a mess. The 3.0mc marker needs a lot of gain, and the either the 3.58mc has too much gain or the 4.1mc needs more gain.
https://i.imgur.com/nYFT040.jpg

Zenith Service Manual CM-105 (25MC33 Chassis)
https://i.imgur.com/vNUGYCL.png

SAMS directions (Folder 757, Set 4)
https://i.imgur.com/DTkwQAi.png

For now I skipped the Zenith direction around replacing the 8.2k damping resistors and simply followed SAMS, unfortunately I could not get the proper response curve by adjusting L17 and L19. first up I will try some different 6KT8 tubes before pulling the chassis out to further investigate.

See the following post for the color circuit schematic from the Zenith Service manual. I have marked in red the relevant Zenith and SAMS coils and test points. Highlighted in green are out of spec parts I earlier replaced, note A3 is an integrator (Zenith part number 87-9), I edited the schematic to show the parts used to replace.

https://i.imgur.com/GRsnGXZ.png

I tried swapping out the two 6KT8 color amp tubes and seen some improvement from changing the first color amp tube (V6) but still not getting enough response at the 3.0 marker.

https://i.imgur.com/VxxXnFC.jpg

I’m confused... since the scope photo is posted upside down, what is the marker directly above the Tektronix “x”? :scratch2:

jr

The lower right marker is the 4.5mc marker. I flipped the scope picture so to match the Zenith Service manual figure 14 reference. See my above post for the picture.

How much does the 3.08 MHz marker move when you adjust L17/A26?

Here are the curves when adjusting L17 (1st Color Amp Plate Coil) for min and max 3.08mc response:

https://i.imgur.com/pvGghdS.png


Also for reference below are the responses when adjusting L19 (2nd Color Amp Plate Coil) which is used to minimize the 3.58,mc response, pics showing min, middle, and max adjustments:

https://i.imgur.com/TCWQGOC.png


In looking over the full color alignment directions the Zenith manual notes to perform the color amplifier alignment first via adjusting L17 and L19 as the color sync alignment will be affected. Also interesting that SAMS alignment directions are the opposite and have you do the color amplifier alignment last.

Question how much affect will the remaining alignment affect the color amplifier response? I am curious if there is an issue with the color amplifier circuit or if the issue is further misalignment. I might pull the chassis and double check to ensure I didn't make any repair mistakes. The earlier posted schematics highlights replaced parts, mostly way out of spec resistors and then film capacitors.

Note there are a couple of suspect ceramic capacitors that in-circuit measure over the 10% spec:

C54 - .0047uf 10% 500v measures .003739uf 20% low, maybe an issue?
C55 - 47pf 10% N75 500v temp measures 54pf 16% high probably good if I pull a lead to measures
C59- .001uf 10% 1kv measures 840pf 16% low, also maybe a problem?
C61- .001uf 10% 1kv measures way high probably getting in parallel capacitance somewhere

C54, C59, c61 are bypass caps not likely to be a problem unless far too small.
C55 looks like it could load T9, maybe check it and the resistors on the other end of it in the burst amp circuit?

I forgot - did you check the 8200 ohm damping resistor connected to T19? How about C58?

Have you also checked all T19 windings to make sure nothing is open?

I went in and measured all of the parts in the color amp and burst circuits, pulled leads where needed. All of the coils and transformers seem to measure ok via resistance and inductance measurements. All resistors and capacitors are in spec except the following:

C54 - .0047uf measures 21% low
C59 .001uf 1kv - measures 16% low
C61 .001uf 1kv - measures 18% low


The only other thing I noticed is the 2nd color amp tube socket appears in poor condition, its the wafer style socket and its bowed down. I will do some further continuity tests while wiggling and also will try to wiggle the tube once I get the chassis back in place. I will replace the above capacitors and report back. Also getting at the 8.2K damping resistor is a real pain, I'm a bit surprised replacing this with a 100K test resistor was part of the Zenith service manual alignment process. Note SAMS simply skips this step.

https://i.imgur.com/DnOgp5b.jpg

I am studying the schematic and noticed that the earlier 25MC30 chassis used a 270K resistor on grid 1 (pin 1) of the 6EW6 burst amp tube and the later 25MC33 chassis switched to a 150k resistor. Thoughts on the design reason for the slight change?

For reference these two chassis are probably 99% identical, my chassis is stamped 25MC33 but must have been an early one as most of the changes for the later chassis are not present on my chassis to include it using the early design 270k resistor.

No idea why they decided to change the resistor value.

By the way, you said the 8200 ohm is hard to get to. Were you able to check the coil winding it is attached to?

I removed the coil from the chassis and then was able to remove and measure the 8.2k resistor. The resistor measured 8.24k. Also the 36pf capacitor measures 36.14pf. I have a used pull spare transformer so I could measures against each other measure, they are very close in resistance and inductance so I assume good vs both bad.

In Use

Coil 1: 2.94 ohms (37.6uh to 68.8uh)
Coil 2 (with center tap): .97 + 3.11 ohms (67.58uh to 120.5uh across full coil)

Spare

Coil 1: 2.91 ohms (38.27uh to 70.45uh)
Coil 2 (with center tap): 1.03 + 3.08 ohms (68.57uh to 123.3uh across full coil)

I have replaced the out of spec capacitors but get the same response. Something interesting; the directions state to set the color level to the mid-point, I found turning the color level to approx 1/4 I could get a much better response curve.

I pulled the lead on the color level pot and did some measuring, the spec is 25k, mine measures 1.78 ohms to 29.624k. The taper appears to be a steep logarithmic curve, my mid-point measures 1.375k, and the 1/4 setting is approx 700 ohms. Someone with math skills could probably calculate what the midpoint value should be for a 25k pot. Directionally I know my midpoint is shifted up since my pot measures high.

https://i.imgur.com/djfD8I2.png

SAMS shows the color level replacement as Mallory part number PP253R which uses their #2 right hand logarithmic taper. The chart shows at 50% it should be at 90% resistance (2.5K where mine measures 1.375K). Now it's possible that Zenith used a special logarithmic taper and the Mallory part is all that was available for the aftermarket.

It's odd that my pot being 20% high measures lower than what the Mallory chart says it should be but also odd I need way less resistance to get a good curve (300 to 700 ohms is the range that appears to be a happy medium when adjusting L17 and L19 yield a proper response curve).

Should I move on or does having to set the color level way high (1/4 turn from max) suggest there are other problems?

*Edit* The other factor is the signal level from the B&K 415 going into C1, I have it maxed out but as I turn it up I am able to back off the color level just a small bit. I suspect the only issue is I don't have enough signal strength going in. :( In the subsequent Zenith Service Manual (CM-107) for the next roundie series chassis the directions include a note that the signal generator and scope may need to be set near the maximum, but don't overload.

https://i.imgur.com/2xQ6Z5V.png

Are there any instructions for tuning L18? The symbol indicates it is tunable. Since the odd response occurs when adjusting the color level control in parallel with it, L18 may be the problem.

I would not be concerned about the mismatch of the log curve as long as it is in the right direction.

I'm guessing now that L18 is supposed to be self-resonant at 3.58 MHz, and the purpose of setting L19 to minimum at 3.58 MHz is to flatten that peak. So, it looks to me like L18 is tuned to too high a frequency. When you turn the color level, the peak should go up and down at 3.58 MHz, not at the higher frequency shown.

Continuing along the next few steps went well.

Color Sync Alignment

Color switch on, color level set to the halfway point
Color Bar generator connected to antenna terminals set to Color Bar Pattern
Connect a .01uf capacitor from test point L to ground
Ground test point K
Adjust L34 for zero beat on screen and minimum movement of color bars through picture (they were visible and a very slight adjustment removed these)
Next set VTVM to +50v DC range
Connect VTVM to test point V, adjust T20 top slug for maximum indication (very little adjustment was needed)
Connect VTVM to test point V, adjust T20 bottom slug for minimum indication (very little adjustment was needed here too)
Note T20 slugs should be on outside end of coil not towards the middle
Remove ground from Test Point K and .01uf capacitor from test point L
Color switch on, color level set to the halfway point
Color Bar generator connected to antenna terminals set to Gated Rainbow
Connect scope to test point R, adjust L29 Burst Amplifier Plate coil to match Figure 15A (a small amount of adjustment was needed)
The second and forth bars should be equal in amplitude
https://i.imgur.com/PtsJDdZ.jpg
Connect scope to test point S
If needed touch up T20 bottom slug quadrature coil to match 15B (a small amount of adjustment was needed)
5th and 7th bars equal in amplitude
Note slug should require a very minimal amount of adjustment
https://i.imgur.com/eqDMPAr.jpg


Color Level Adjustment

Color Bar generator connected to antenna terminals set to Color Test Pattern
Connect scope to test point R and set color level to minimum
Adjust L18 for minimum color output at test point R (a very small amount of adjustment was needed)
Essentially the picture should be black and white only


Range Check of Hue Control

Color Bar generator connected to antenna terminals set to Gated Rainbow
Connect scope to test point R and set hue control to maximum counter clockwise
First and third color bars should be equal in amplitude (second color bar maximum)
If not touch up L29 Burst Amplifier Plate coil for equal amplitude of first and third color bars (a very small amount of adjustment was needed)
Connect scope to test point R and set hue control to maximum clockwise
4th and 5th color bars should be equal in amplitude (they were)
Note if only the 3rd and 5th color bars can be made equal than this is acceptable
Connect scope to test point R
Set hue control for equal amplitude of 2nd and 4th (3rd color bar at maximum)
Now connect scope to test point T
Color pattern should appear as shown in figure 15C (No pic but it matched)
https://i.imgur.com/GQNDsg4.jpg


Alignment Points
https://i.imgur.com/whehTAk.png

I'm guessing now that L18 is supposed to be self-resonant at 3.58 MHz, and the purpose of setting L19 to minimum at 3.58 MHz is to flatten that peak. So, it looks to me like L18 is tuned to too high a frequency. When you turn the color level, the peak should go up and down at 3.58 MHz, not at the higher frequency shown.

I just posted the next few alignment steps as I just moved along for now with the color amp alignment as-is. I will go back and see what interactions I can get with the color level, L18, and L19. Note L18 measures ok so I believe it to be good. Also note the voltage going in at C1 from the B&K 415 is 0.3207 volts.

After going through the other alignment steps here is what the Video Amp test point U with the color level set at the half-way point, it looks better than before.

https://i.imgur.com/ziRmbQX.jpg

Also here are some videos (note they should open in Imgur, let me know if they don't work)

Adjusting the B&K 425 signal down to zero and then back to max, curious if more B&K 415 gain would prove a better response curve: https://imgur.com/jmoT9J0
Color level starting at the minimum and then turning the potentiometer to the maximum: https://imgur.com/5RBpapN
Adjusting L19 (2nd color amp) which should be adjusted for minimum 3.58mc response. I starting with the slug at the top and turned it down to the bottom: https://imgur.com/lVtZ9qK

First video: looks like maximum 415 drive is overloading the set and giving a false flattening of the curve by crushing the peak. Don't try for higher, in fact make sure it's not too much.

Second video: yikes what mess! Stick with the suggested half-way setting for now.

Third video: There is only one point that gives a symmetrical response about 3.58 MHz?

Seeing the correct two nulls for L19 may be confused because you aren't changing the damping resistor.

Again, this suggests to me to adjust L18 so the peak goes up and down at 3.58 with color level adjustment, and adjusting L19 in conjunction with L18 for most symmetrical response.

I tried adjusting L18 with the goal of having the 3.58mc peak go up and down with color level adjustment. I also kept the B&K 415 signal turned down a bit from max. I don't know that I got it much better, video: https://imgur.com/A9hrDx1

I have checked all of the parts in the color amp circuits and I believe they are good, I have tried alternate 1st & 2nd color amp tubes, and made coil adjustments but the 4.1mc marker always has a much stronger response and it takes the color level at about 70-75% before the curve looks correct. Note probably unrelated but the last step of the color alignment is the 3.58mc traps which I got confused on and did not adjust the traps yet.

I will reset, look everything over, try again, and report back. old_tv_nut, thank you.

OK, but after adjusting L18, did you try readjusting L19 to get things flatter?

A few more actions and notes:

L18 (Color Level Coil) - tried to adjust it against different L19 and L17 coil settings. At the extreme it amplifies the 4.08mc marker which does not help, for now I settled on when the color level is set to the minimum then setting L18 to have what would be the 3.63mc marker at minimum which leaves the 4.08mc and 3.08mc markers at the same level, this is also about what is done in the Zenith color level directions, example below. Note this image is with with the B&K 415 signal turned up, at lower settings this is a flat response.
https://i.imgur.com/jR82zGz.png
L19 (2nd Color Amp Coil) - when adjusting the slug starting with it at the top (nearest to chassis) the 3.58mc marker has the largest response (like a bell curve) with the 3.08mc and 4.08mc markers both lower. As I turn the slug down the 3.58mc start to fall, previously I kept turning the slug until the 3.58mc marker was just to as low as it would go. In doing this the 4.08mc markers would gain strength and throw the curve off, extreme example below.
https://i.imgur.com/NViTFYf.png
Today for L19 I instead only turned the slug down until the 3.58mc marker just fell below the 4.08mc marker, note the 3.58mc marker can be further decreased but at the expense of the over all curve, maybe this is a 1st of the two dips that would be seen with the VTVM.
L17 (1st Color Amp Coil) - As I adjust this coil there appears to be a center area on the slug which brings the 3.58mc marker to it lowest and then starts to provides some over all curve gain, eventually the 3.08mc marker starts to drop off, I stopped right before this point. Further adjustment will cause the 4.08mc and 3.58mc markers to increase but then the 3.08mc marker will start to decrease.
Note no combination of adjusting coils would yield individually strengthening the 3.08mc marker response.
The strength level of the B&K 415 does affect the curve, would it be fair to assume that I should keep the level turned down so that at max color level there is no clipping?
Several videos below, note I feel like the color amps are turned way down, i.e. the previous setting provided lots (maybe 2x) gain, maybe that is ok...
Here is a video starting with the color level at minimum and going to maximum, note I have the B&K 415 signal strength set so that a maximum color level there is no apparent clipping (curve flattening): https://imgur.com/YFLdxcx
Here is a similar video starting with the color level at minimum and going to maximum, but have the B&K 415 signal strength set to maximum: https://imgur.com/l563K5B
Finally here is where I have landed for now: the response curve with color level set to the midpoint and the B&K 415 signal strength set to avoid clipping.
https://i.imgur.com/2gv49wR.jpg


One option would be to pull the 8.2k resistor, add the 100k resistor and via a VTVM adjust the 2nd color amp coil to the 1st dip (nearest the chassis). I am confused by the directions, it notes to disable the sweep but to pass in the 3.63mc marker, the B&K 415 combines these functions so not sure how I would do this. What is the VTVM measuring, I assume overall voltage. Does a single marker act like a signal generator?
https://i.imgur.com/hplROKV.jpg

Would there be an affect on the color amp response from the other color circuits such as the oscillator or demodulator? To get the TV up and running I avoided replacing most all ceramic capacitors. Below are the ones that measured way off.

C92 & C93 - all 4 .001uf measured 18-21% low
C103 - .001uf measured 19% low, is this just for bypass? or would this affect the 3.58 oscillator
C104 - 100pf measured 17% high but this was measuring in circuit, I suspect this will measure right on if I pull a lead
C67 - 100pf measured 28% high but this was measuring in circuit, same thing I suspect this will measure right on if I pull a lead
C69 - .001uf measured 18% low
Note capacitors under 100pf may have measured high or low but without pulling them complete out they are hard to measure and I am assuming they are ok.

https://i.imgur.com/ovZnhb2.png

https://imgur.com/YFLdxcx -- increase is linear, shape doesn't change - very good measurement conditions.

https://imgur.com/l563K5B -- obviously overdriving and distorting at higher levels

"Would there be an affect on the color amp response from the other color circuits such as the oscillator or demodulator?" - No.

"where I have landed for now" - I'd say leave it this way for now and see how the picture looks, but it still is strange that you cannot get the response higher at 3.08 MHz.

Could you remind me where on the schematic is the sweep signal injected?

Sweep injection for the color amp alignment is at C1 which is just after the IF picture detector diode. This bypasses all of the IF alignment circuitry accept the 4.5mc filter (which I fiddled with just to see if it had an affect, nope it just shifts response curve left or right of the 4.5mc marker)

I agree it is strange I can not get the response higher at 3.08mc. I would like to think it is not something dumb with my testing setup or tools. Thinking though could an out of spec coupling capacitor pass but attenuate part of the frequency response? Otherwise I am looking at LC circuits which all have been gone through.

Could I create a test point after the first color amp circuit, or at other points to see where I lose the response? Thoughts on where in the circuit?

For Reference here is the full Zenith CM-106 Service Manual Schematic: https://i.imgur.com/i1nBrxi.jpg

Here is what I get off of the cathode of the 2nd color amp tube and a 150 ohm resistor (measured here as this resistor is soldered into a pin that is assessable from the top. Color level set to mid-point, I will assume the peak is at 3.63mc, here too the 3.08mc has a reduced response. As expected at max color level there is no signal as the pot goes to zero. Adjusting L17 only increases or decreases the overall response curve while holding the 3.63mc marker at the peak. I also tried to measure at Pin 7 of the first color amp but the signal was too low to really measure.

With the directions for L19 to minimize the 3.58mc marker I assume that leaves the earlier circuitry to provide an overall response curve wide enough to cover 3.08mc through 4.08mc. Here with the 1st color amp the center point seems like it should be shifted in frequency a bit lower.

https://i.imgur.com/pVjCH4J.png

https://i.imgur.com/pahZLPM.png

Reading the Color TV Training Manual 3rd Edition. Below is the overview for the chroma bandpass amplifier. Conveniently they picked a Zenith circuit as an example, they note is that the 7pf capacitor blocks the luminance signal, if this capacitor was off spec a bit could it attenuate towards the 3.08mc signal?

https://i.imgur.com/CswcpyD.jpg

One more post from reading Basic Televisions Principles and Servicing Forth Edition. Here their section on the chroma bandpass explains that the chroma amplifier circuit should peak a little above 4.1mc so when fed from the IF circuit you get the typical textbook response. This would still suggest the response I get out of the 1st chroma amp is not peaked correctly, so who know what the issue is with my chassis.

https://i.imgur.com/q6zAbLJ.jpg

https://i.imgur.com/3VVROr0.jpg

The reponse at the "new test point" (top of color level control) confuses me. If it is supposed to control color level, its peak effect (due to L18 resonance) should be at 3.58, in my opinion. I can't understand why they would want the symmetry of the response to change with color level setting.

Try this: change your test point to the cathode of the second amp (pin 6 above the 150 ohm) and turn the color level to max to take L18 out of action. See what the response is and what effect tuning L17 has. Then maybe we can go from there.

"the chroma amplifier circuit should peak a little above 4.1mc"
True, and I would expect to see that if you look at the 2nd amp cathode with the color level set to max. However, I would then still expect to see L18 tuned to 3,58 MHz so that the whole sloped response goes up and down with the color level control.

Note that this means that you would still expect to see a sloped response at the final test point (cathode of the R-Y Demod) because the injected 3.58 sweep has not been RF modulated and passed through the IF. So this makes the illustrations of final flat response suspect.

Note the text "If you were to align only the chroma bandpass amplifier...this method is rarely used however." So they are recommending injecting an IF sweep instead of the 3.58 MHz sweep. AND the symmetrical sketches shown with the 3.58 sweep injection are bogus.

So two important comments were made tonight, the extra studying was good too:

I would like to think it is not something dumb with my testing setup

recommending injecting an IF sweep

These made me go back and think about the signal going in. So the B&K 415 output has several setting, I assumed since I am feeding in signal post video detector I should use the video function. I just changed the output function to IF. Am I on the right track here? Note now I need to have the B&K 415 gain set to max. See below for the same setup just switching the output function setting and signal attenuation.

https://i.imgur.com/nEXvkwB.png

https://i.imgur.com/BHZhvQO.png

The B&K 415 manual does outline using the video function for the chroma circuit alignment, so I'm not sure what to think, it is also possible there is an issue with my B&K 415 :(. Maybe others with a B&K 415 can chime in. Note section 8.5.3 goes on to say its easiest to just continue on from IF alignment to chroma alignment by keeping the signal probe connected to the tuner (I assume here is when you would keep the function set to IF), then simply switch to the demod probe and continue on.

https://i.imgur.com/1thSozc.jpg

Ok, when you switch the B&K to IF but inject at C1, you apparently get some video detection action, I guess. But there's no telling if it is loading any traps correctly.

The next thing I would try is leaving the B&K output set for IF but moving the injection point to the IF input/mixer test point. With all the IF and trap stages in operation, it may make the curve even closer to ideal.

Question: when you changed output to IF, did you need to adjust sweep width/centering to get the chroma bandpass curve centered on the scope?

Ok, when you switch the B&K to IF but inject at C1, you apparently get some video detection action, I guess. But there's no telling if it is loading any traps correctly.

The next thing I would try is leaving the B&K output set for IF but moving the injection point to the IF input/mixer test point. With all the IF and trap stages in operation, it may make the curve even closer to ideal.

I would agree and will do this next. Thank you.

Stay tuned for a troubleshooting interruption. While still connected at C1 I was double checking the response curve and the waveform started to get erratic and now only has a minimal response curve. I pulled the test equipment and I have a very blue screen and basically no color, something failed.

Not sure what the root issue(s) were with the problems I had. As noted above first there was an issue with the color amp signal which occurred as I adjusted the Heathkit IG-5240 pocket signal generator, I fiddled with the controls which maybe was my problems.

From there after pulling and putting the chassis back in the issues changed to diagonal lines of signal against a white screen and then later a bright but faint image. The IF and color amp signals now looked correct so I poked around in the AGC and video circuit, all parts in these circuits measured ok. The Zenith Color TV Service Manual by R.L. Goodman has a section on actual issues and resolutions. One issue noted: Washed-out picture, no sync. AGC, sync trouble. Set may have to warm up before picture fades out. The cause was a leaky or shorted .01uf capacitor at grid, pin 5 of the sync - AGC tube. The capacitor tested ok but regardless I replaced it, was this the issue, I don't know but the set is back working.

https://i.imgur.com/91ELGGf.png

Back to the alignment:
Question: when you changed output to IF, did you need to adjust sweep width/centering to get the chroma bandpass curve centered on the scope?
I did not need to change the sweep width/centering. The only change needed is with the signal output and scope vertical settings to get the response curve to show well on the scope screen. The Zenith Service manual does not show what the curve response should look like when feeding the sweep generator through the tuner and IF sections but I assume it looks good. I still get a lower response for the 3.08mc marker when connecting at C1, maybe this is an artifact of the test equipment? Note when connected at the tuner adjusting L17 does a nice job of balancing the 3.08mc and 4.08mc markers, I assume they should have an even response.

https://i.imgur.com/jky4Opv.png

Question: Which input should I trust for the color amp alignment in regards to feeding the B&K 415 signal into the tuner vs test point C1 (post video detector)?

Connecting the B&K 415 to the tuner with the output set to IF I can adjust L19 to where I see the 3.58mc marker decrease and then have a defined low spot, also L17 allows me to create a flat-ish response with the 3.08mc and 4.08mc markers even.

Below is the optimized response curve with the B&K 415 signal input at the tuner, the 3.58mc marker is at its lowest response, and then the 3.08mc and 4.08mc markers are even. The 2nd pic is then the resultant response curve when moving the input to C1 and setting the output to video, note leaving it on IF works but barely yields a response curve. I am inclined to think I have it set correct this way and the "odd" response curve at C1 is due to the B&K 415 vs a mis-alignment.

https://i.imgur.com/wYuARxf.png

Your final result with the B&K 415 input to the tuner is obviously correct.

It's the overall result of signal going through the whole chain from tuner to picture that needs to be correct. The odd result when going in at C1 may be the result of the video detector circuit being loaded by the signal cable, plus, it is possible that both the SAMS and the Zenith documents are screwed up in not recognizing that the chroma bandpass by itself should have a tilt that compensates for the IF response.

Declare victory and move on!

I went back through the subsequent color alignment steps to double check everything. I posted directions back a few pages. The only notable item was for the color sync alignment you adjust L34 for zero beat on screen and minimum movement of color bars through picture. This was very dependent on fine tuning and my rf converter and signal bar generator both require a bit of different fine tuning. Adjusting to the signal bar generator probably means the rf converter could be off, maybe there is plenty of "wiggle" room with this adjustment.

The last color alignment step is to adjust the 3.58mc traps. The directions are to connect a color bar generator to the antenna, connect the scope to test points RR, SS, & TT and adjust each trap for minimum for minimum 3.58mc response. My question, what am I looking at on the scope and what component is the 3.58mc response?

https://i.imgur.com/WjX0PVz.png

https://i.imgur.com/ESb7bky.png

1) It seems odd that the color oscillator beat frequency should be affected by fine tuning, but is very normal that when adjusted using one source it will be different with another source. It depends on whether the sources are close in color subcarrier frequency or not.

2) At the horizontal sweep rate you are using on your scope, adjust the 3.58 traps for minimum "fuzz" (trace thickness), which is caused by residual 3.58 MHz at the output of the demodulators. You may also be able to see the 3.58 MHz in the picture as a fine, moving dot pattern.

Sometimes when chroma osc lock is effected by fine tuning it is a result of the horizontal hold being set to the edge of lock and the flyback winding pulse that gates the burst isn't lining up with the burst.

I am calling it done. The set has a much better picture, probably not perfect but I am very happy. Maybe related to the full alignment or maybe due to the new to me Blonder Tongue BAVM-860SAW modulator but I no longer get horrible noise during commercials transitions which made it un watchable before. Next will be a final color purity and convergence once I get the set brought into the living room.

A special thank you to old_tv_nut. Your help and advice very much appreciated.

Pictures, please!

Some pictures below to include the Danish modern cabinet and also my test bench setup. As I look close I see some ghosting or smearing, maybe an artifact of the setup and adjustments, also the CRT in the cabinet should be a bit stronger so the guns and contrast can come down.
https://i.imgur.com/0gmldVs.jpg

https://i.imgur.com/A6xS2sT.jpg

https://i.imgur.com/sNXAoFq.jpg

https://i.imgur.com/HfuyFBi.jpg

https://i.imgur.com/iSJkKmi.jpg

https://i.imgur.com/8MaO7cn.jpg

Thanks!