Ok so I have yet another one of these Motorola sets its been recapped power supply and all the wax caps got a great picture and sound but the vert hold works but won't lock, I can get the pic to stop but it won't lock at all. Checked the resistors on the hold and size pots and are good I subbed the 1000 pf and both the 100 and the 250 pf Micas and made no difference. I have the 2 tubular caps in the verticle and are the correct ones .0047 but I have 2 .002 10 kv ceramics in the horizontal I know there should be the correct tubular caps in there but the horiz is stable and ok. Checked other resistors around the 6sl7 and all are within range. Any ideas how to get this to stop rolling and lock. :smoke:

Sounds like your vertical oscillator and output are working ok... I would check back farther, around the clipper/sync amp (v-11) and the integrator network for bad or miss-wired parts.

jr

If it can roll both directions, and especially if you can get it to stop, then your V osc. is probably fine. Lack of lock is usually lack of sync in that case. Since you have H sync the sync sep is probably somewhat functional.

My first step would be to change out all the parts that couple the sync sep to the V osc. and verify the values of what is in there now against the schematic while doing so. If your set matches the below schematic R-44,45 and C-47,48, 140
http://earlytelevision.org/images/motorola_VT71_TS4J.jpg

I don't see how the osc could run and at the same time cause the sync issues so if those parts are not the problem look for weak sync sep output next.

Ok, r44 and r45 check good and c47 and 47 are .01 caps and are new I replaced and I did check all the caps when I got them so as I didn't introduce any other problems to follow with defective caps and c140 is a 250 pf and this is one I subbed already with a 251 pf mica and no change. All the tubes are fine but maybe I should try other 12sn7 tubes. Other resistors like the 2 1 meg resistors are good also.

I don't know but could the .002 ceramic caps in the horizontal be interfering with the verticle sync ? The correct caps that should be in the horiz is .001 but tubular type . Although the horiz is fine and stable. I can't find anything else wrong here and tried several different 12sn7 tubes and 6sl7 tubes also .

Best tool to find the fault will be a scope, with a isolation transformer to plug the set into. We do not want to do harm to any gear, tv, or tinkerer for that matter. Without the scope you are just making wild guesses as to what the fault is. All the best,Tom.J

I don't know but could the .002 ceramic caps in the horizontal be interfering with the verticle sync ? The correct caps that should be in the horiz is .001 but tubular type . Although the horiz is fine and stable. I can't find anything else wrong here and tried several different 12sn7 tubes and 6sl7 tubes also .

Not likely... I would recheck the wiring between the sync clipper and the vertical oscillator tube... it appears that the vertical sync pulses are not reaching the vertical oscillator. Perhaps a side by side comparison to your VT-73 would reveal an error or wrong part. :scratch2:
Of course, a scope would tell you in seconds if the vertical sync pulses are wrong or missing.

jr

Best tool to find the fault will be a scope, with a isolation transformer to plug the set into. We do not want to do harm to any gear, tv, or tinkerer for that matter. Without the scope you are just making wild guesses as to what the fault is. All the best,Tom.J

Not likely... I would recheck the wiring between the sync clipper and the vertical oscillator tube... it appears that the vertical sync pulses are not reaching the vertical oscillator. Perhaps a side by side comparison to your VT-73 would reveal an error or wrong part. :scratch2:
Of course, a scope would tell you in seconds if the vertical sync pulses are wrong or missing.

jr

Exactly. [starts chanting] Scope!.. Scope!.. Scope!... :D

One other thing you may be able to do is try injecting V sync from the VT-73 (or a B&K analyst or test pattern gen) into the VT-71. Make sure the hot chassis polarity matches before applying power or bad things could happen.

The high voltage caps coupling the circuits won't work right, either, if they are ceramic disc..
Those were originally .005 10 KV for vertical, and, .002 10 KV.
I may have my caps mixed up, but, I'm pretty sure on voltages on both. The cap on h. v. rectifier should be either .001, or, .005 at 10,000 volts.


I think they actually work at seven thousand volts.

The high voltage caps coupling the circuits won't work right, either, if they are ceramic disc..
Those were originally .005 10 KV for vertical, and, .002 10 KV.
I may have my caps mixed up, but, I'm pretty sure on voltages on both. The cap on h. v. rectifier should be either .001, or, .005 at 10,000 volts.


I think they actually work at seven thousand volts.

Wrong. Every unrestored Moto VT-71 / VT-73 I've seen has 6KV rated HV caps, and the schematic linked above shows .001 on the H deflection plate couplings.

The HV coupling caps don't work well if ceramic (unless you increase the capacitance), but the only HV ceramics he says are in there are in the working Horizontal section....Add to that that it is a NO sync issue in the vertical (and not a sweep size/linearity issue, which is what HV cap issues would cause) and the HV caps should basically be irrelevant to the problem described.

Sorry. It's been a long time.

There is a .004 mfd paper cap from the vert oscillator to ground. It is the only .004 mfd cap in the set, and that cap is definitely leaky. Change it, with an exact .004 mfd cap, and that should solve the problem. A .0047 cap will not replace the .004 mfd cap.

There is a .004 mfd paper cap from the vert oscillator to ground. It is the only .004 mfd cap in the set, and that cap is definitely leaky. Change it, with an exact .004 mfd cap, and that should solve the problem. A .0047 cap will not replace the .004 mfd cap.

Ok I now have vert sync lock, and the .004 I did change I know that one is important. I'll post what the problem was shortly.

Well with this set upon looking it over for the first time I found a .001 tacked in place of a 250 pf but the 250 pf was not where it normally is, tucked under a tie strap and hard to see because a 1000 pf mica normally sits in front of the 250. So I mistook that 250 for another one nearby and after seeing the Motorola schematic for the ts4j that I have I was thinking that 250 pf was a possible production change because it was not there along with the 22 ohm resistor within the ballast is not wired for this set. No old solder, nothing it don't have it but the schematic shows the ballast has it but yet could not find it on the schematic. So some was my overlooking thinking changes were made back in the day. So I put the 250 in which was infact c140 and that fixed the problem. Thanks for the help guys.

Ok while I have verticle lock now I can get the pic to stop rolling but when it's stable it gets Alittle jitter then starts rolling again every minute or so. Could this be from the IF maybe channel 3 is not tuned perfect, although the picture is good.

Try a different modulator, and try reducing signal to the set as well as increasing it (IIRC contrast is IF gain+video gain so try changing contrast first*).
* best to do this with a DVD or some repeatable content that does it bad so you can see how the signal level affects it....Also don't worry about watchable brightness or contrast during this test, as long as you have enough to tell if it is rolling that is all that matters.
If signal is too strong or too weak then it will fall outside the designed range of the sync clipper resulting in weak sync or sync with noise (which can disrupt lock).

If it looses it under the same conditions regardless of signal then the sync sep and osc stages should be suspected.

Well I have been running it with the cable wire I was not using an RF modulator so this should be good enough to figure what is what with the signal or sync. I wonder if the 2 .002 ceramic disc caps I have in the horiz may be affecting the sync.

I just checked v10 clipper tube pin 6 should have b+ at least 125 Vdc on it but all I'm getting is 82 Vdc it don't make sense to me I checked the cap that feeds pin 6 even tried another cap but only 82 Vdc so that should indicate weak sync . This is one of the power supply caps and recapping I did one at a time and never messed up with power supply caps so now I'm stumped. I did replace the seleniums with 1n4007 diodes as I done with the other sets I have with no dropping resistors.

Assuming the whole B+ rail is low and not just the sync tap:
B+ is created from B++ at the audio output tube which acts as a B+ dropping resistor.
Check the bias on the audio output tube, the tube it's self and associated parts....If those are good look for excessive loads on the B+ rail (by disconnecting things hooked to B+ one by one and noting voltage change or by resistance testing).

[edit] Scratch the audio output tube being the B+ supply divider resistor, the circuit does not look right for that...Odd thing is I'm not seeing any clear B+ supply/divider...Might be time for some coffee.

You're right, it's not the usual stacked design using the audio output tube. Instead B+ is created by the drop from several tubes. Sorry for the poor scan quality.

https://farm3.staticflickr.com/2876/34158529461_e7e3b59812_o.png (https://flic.kr/p/U3toK8)

timmy if you have not done so already, down load the Motorola manual on the VT-71 from the ETF it gives detailed description of the circuits and bite size schematic of each section of circuitry. Hopefully will make it a little bit easier to follow. All the best,Tom.J

Ok yes I have the schematic for the ts4j ill look at it closer. So if I'm correct this could be the vert problem not staying locked.

If your picture is crisp, and, clean, I would say it's more likely in your sync circuit somewhere. Perhaps the sink clipper..

If your picture is crisp, and, clean, I would say it's more likely in your sync circuit somewhere. Perhaps the sink clipper..

Well it's not really crisp it's close but not crispy which is nice to be coming out of a 70 or so year old tv. I'm going to get into it today to see if the whole b+ rail is low. Maybe a defective diode I put in.

Given the explanation of the B+ source that bob posted, if B++ is right then PS diodes should not affect the B+ .

It looks like B+ is obtained by a balance of net currents and voltage drops through V-2,4,6, 10a 11A, and 12 (if I'm reading correctly). Basically B+ is created by a voltage divider created by the impedance of each tube connected to it....It is like the audio output B+ divider/dropper concept I thought it was, on crack (ie they took it too far).

To figure out the low B+ issue you are pretty much going to want to examine the biases of all the tube sections it feeds look for bad tubes, and bad passive components. You will want to look for bias voltage changes in tubes that are not immediately explained by changes to the B+ rail.

Tubes shown in Bobs diagram between B++ and B+ will be conducting too little and or tubes shown between B+ and the Common B return/b- will be conducting too much.

SS sets that use this type of multi-stacked parallel B+ (I hear 2 way radios do this a lot) can be a b!tch to troubleshoot.

So the low value resistors between the heaters I should check. Could this be a tube drawing to much current ?

He doesn't mean the tube heater (filament) is drawing too much current. He means that if the tube grid bias is off, it could be drawing too much or too little current between the cathode and plate.

So the low value resistors between the heaters I should check. Could this be a tube drawing to much current ?


I don't see any interaction between the heaters and the B+, so I don't get why you are asking about the heaters (they should not matter).

As I said in my last post your B+ issue is the lower tubes in Bobs diagram conducting too much current or the upper conducting too little...

The B+ voltage is created from the B++ through use an interesting idea: If a tube draws a certain amount of average B current and drops a certain amount of average B voltage, then (if you filter the spikes out) you can model a tube stage as a power resistor loading the B supply....They modeled several lower B+ voltage stages as resistors then connected those stages to B++ in a series parallel voltage divider network the center of which is B+.

If your not an electrical engineer, and don't understand: Ohm's law, series and parallel resistor networks, and the voltage divider rule then it will be extremely difficult to understand the way in which the B+ is obtained in this design*, and how to best troubleshoot it.

*It is probably the most complex unregulated supply I've seen in tube era electronic gear.

Well if there are bias issues somewhere I have not found any high or low value resistors that were bad . I have a Dvom that I can check capacitance on capacitors so I am wondering if I got a possible bad cap because I know when you get small waves in the picture that usually means a bad cap , not filtering the ac out and that's really the only noticeable thing other then the weak vert lock that I see going on with this set because of probably the low b+ . So now I should look into the caps in the p s that I put in as possibly bad. And I do know it uses half to get the 125 Vdc for the b+ . So now I will have to doubt my Dvom for cap checks if I find a bad one.

I don't know if it's feasible to remove each b+ wire at the tie point one by one as I think there are like 4 or 5 places b+ Is tied to, maybe narrow down where the drop is originating from. The b++ is where it should be on the chassis at 248 Vdc and there are different voltages on each p s cap and the next to b+ voltage is 132 Vdc . I don't have any voltage chart that is with some schematics as it's just the download from early television and it's kind of difficult to judge what's right or wrong if I don't have any references to go by.

Timmy, you will find at the ETF scans of folders 55-16 and 71-12 which are the TS-4 series chassis. They have a voltage and resistance charts with in. They also have 83-6 which is the TS-18 that is like the-4j late chassis with the same charts as the other two.
All the best, Tom.J

I have voltage charts for the ts18 and another one but there are little changes that I'm not sure if the 4 j would be the same, like production changes which I already found with the 4j. But I'll take alook anyway.

I'm wondering if this set had problems with vert roll many years earlier because when I got this set c140 was not there but rather a .001 600 v was tacked in its place, and not factory soldered then I discovered that c140 was not there so I replaced it after removing the .001 which clearly someone put it there to try to fix something and the cap was a black sprague , an old one done many years earlier. The ts18 tubes for the I f are different then the 4j so the voltages may not be the same. Maybe a ts4d would be closer because it uses the same tubes for the I f. I can't find any info as far as voltage or resistance chart for even the ts4d on ETF maybe someone can let me know where to look to find it.

Ok Timmy, The voltage & resistance charts are in the SAMS folder them self. Sams 55-16 print page 14, pdf page 19_ Sams 71-12 print page 8 & pdf page 8 and Sams 83-6 print page 8 & pdf page 11. Tom.J

Ok Timmy, The voltage & resistance charts are in the SAMS folder them self. Sams 55-16 print page 14, pdf page 19_ Sams 71-12 print page 8 & pdf page 8 and Sams 83-6 print page 8 & pdf page 11. Tom.J
Ok the only SAMs I find that has a voltage and resistance chart is for the ts18 and I can't use it tube lineup is different and almost certain the voltages are different based on what I seen already on the ts4j compared to the voltage chart of the ts18. So if there is a listing for the 4d or the 4j voltage chart I can't find it.
:scratch2:

Ok, question where did you get your copy of SAMS 55-16 & 71-12 from. My pdf copies came from the ETF & the charts are on the pages I listed. Tom.J : )

I got the SAMs for the ts18 from ETF and that one was the only one with the complete schematic. The others for the 4d and the 4j is only the schematic nothing else is there.

Sounds like you click on the link to just the schematics. Look for VT-71 and VT-73 on the ETF site.

Link to Sams 55-16: http://www.earlytelevision.org/pdf/Motorola-VT-71-TS-4B-J-early-Sams-55-16.pdf

Link to Sams 71-12: http://www.earlytelevision.org/pdf/Motorola-VT-73-TS-4J-late-Sams-71-12.pdf

Thankyou for these prints as I don't know why I could not have found these. The 4j is late and the other while seemingly the same the voltages are infact difference then those of each other as well as the ts18 voltages so I should be able to come up with some reason why it appears the b+ is low or being dragged down. Pin 6 of v11 shows 120vdc on the one schematic but the other schematic late ts4j shows 82 Vdc volts but yet same tube and yet 100 Vdc on the 25l6 audio tube, it makes no sense to me how can there be 82 Vdc on v11 and 100 Vdc on the audio tube they are wired in parallel so they should have the same voltage.

Did you see the note at the bottom of the voltage chart ?

V11 pin 6 is connected to pin 4 of v10 (audio tube) and should be the same voltage with respect to B-

The voltages on V11 are measured with respect to V11 pin 6. So pin 6 is 0 volts while V11 pin 5 is 82 volts with respect to pin 6.

Did you see the note at the bottom of the voltage chart ?

V11 pin 6 is connected to pin 4 of v10 (audio tube) and should be the same voltage with respect to B-

The voltages on V11 are measured with respect to V11 pin 6. So pin 6 is 0 volts while V11 pin 5 is 82 volts with respect to pin 6.

Which SAMs are you referring to, 55 16 or the other SAMs. I was measuring the b+ from the positive to the negative I don't see where it shows pin 5 is 82 Vdc the only place I'm getting 82 Vdc is on pin 6 of v11 to common negative. Ok I see what you mean but pin 6 has b+ on it to neg is only 82vdc and should be 125 Vdc but the SAMs shows zero on pin 6 but the other SAMs says 120 Vdc. B+ is on the audio tube and v11 pin 6 . I'm just trying to figure out which SAMs to go by.

Yes, 0 on pin 6 with respect to pin 6. See the cross symbol next to the '0V' on the chart ?

What that means is but the negative lead of your meter on pin 6, not the common negative while taking that reading. So naturally when you also put the positive lead of your meter on pin 6, you will get 0 volts.

I think looking at the contrast control is the easiest way to tell.

The early TS-4J is just a standard three terminal pot.
The TS-4J late has two extra taps and several capacitors mounted on the pot.

Yes, 0 on pin 6 with respect to pin 6. See the cross symbol next to the '0V' on the chart ?

What that means is but the negative lead of your meter on pin 6, not the common negative while taking that reading. So naturally when you also put the positive lead of your meter on pin 6, you will get 0 volts.

I think looking at the contrast control is the easiest way to tell.

The early TS-4J is just a standard three terminal pot.
The TS-4J late has two extra taps and several capacitors mounted on the pot.
Ok the contrast tells, it's early. So if I am to put meter neg on pin 6 then what is positive ? Because positive to pin 6 comes right from b+ Capacitor positive. Well the SAMs, early shows infact pin 6 has 120 Vdc on it so pin 6 to negative should be that of 120 Vdc but it don't . The other SAMs shows zero volts checking the way it says. It don't show any other negative to use, no stars or marks on the SAMs which I would think it's common , on the early SAMs.

Use Sams 55-16 then. Forget about using pin 6 for reference - that was only for Sams 71-12.

All voltages in Sams 55-16 are with respect to common.

Now that you have the correct service info, go through and check all the voltages and try to narrow down the problem.

The contrast control matches mine with the 55-16 SAMs so yes now I'll go over it now that I have something to reference, and thanks for finding these SAMs. I really curious what could pull the b+ down from 125 Vdc to 82 Vdc sometimes 90 Vdc.

Ok I checked resistance on tubes v 2,4,6,10,11,13 all are good except v6 video output tube pins 2,3,4 should have 2k,11.5ohm,7ohm but I am getting on all 2,3 4, between 60 and 100 ohms there are differences between the 3 but amounts are high for the 7ohm and the 11.5 ohm but to low for the 2 k . :scratch2: the resistance numbers match the later SAMs yet the contrast is different so I'm using the ts4j late, 71 12.

I don't know but would heater voltages reflect on the drop in b+ , I ask because I can't seem to get the right ohms readings from several tubes on this set using both ts4j early and late prints along with the ts18 print all show close to the same ohms reading but I'm getting totally different readings so with the b+ down between 82-90 Vdc from 125 Vdc I'm wondering if something affecting the heater voltages if this may affect the b+ . While the 6al5 pin3 7 ohms I'm getting 22 ohms and pin 4 1 ohm I'm getting 16 ohms. V6 pin 3 11.5 ohms I'm getting 22 ohms and pin 4 , 7 ohms I'm getting 18 ohms this don't seem right yet the voltages are ok on v, 2,4,10,11,13,6. It don't make sense that b+ is so low there should be something obvious but I'm not finding it. Any help would be great at this point.

Are all tubes, including the CRT plugged in when you are making the ohms measurment? How are the ohms readings on v9 (12SN7) and v12 (12SN7)? Pins 7&8 are the heaters on the 12SN7s.

jr

Keep in mind that the resistance of tube filament is temperature dependent. I really doubt that is the source of your problem.

Keep in mind what Tom posted earlier. B+ is created by the balance of several tubes. If it's off then either the tubes supplying current are not passing enough or the tubes drawing current are sinking too much. That could be caused by the tubes being bad or they are not biased correctly. Try swapping tube and check the voltages on them.

Are all tubes, including the CRT plugged in when you are making the ohms measurment? How are the ohms readings on v9 (12SN7) and v12 (12SN7)? Pins 7&8 are the heaters on the 12SN7s.

jr

Yes crt plugged in and the 2 -12sn7s, 18and16 ohms pin 8 pin 7 16and 10 ohms. The clipper is 18 ohms and 16 ohms.

Keep in mind that the resistance of tube filament is temperature dependent. I really doubt that is the source of your problem.

Keep in mind what Tom posted earlier. B+ is created by the balance of several tubes. If it's off then either the tubes supplying current are not passing enough or the tubes drawing current are sinking too much. That could be caused by the tubes being bad or they are not biased correctly. Try swapping tube and check the voltages on them.
I already checked voltages on the tubes that are supplied by b+ and they are good this is why it's baffling to me and I did try other tubes,6sl7, 12sn7s, 25l6 even checked resistances of the ballast.

The tubes that supply the B+, not the tubes that are supplied by B+.

B+ is created by the drop across several tubes from the B++ supply.

V1 6AG5 RF AMP
V3 6AG5 3RD IF
V7 6AU6 LIMITER
V11B 12S7 CLIPPER

The tubes that supply the B+, not the tubes that are supplied by B+.

B+ is created by the drop across several tubes from the B++ supply.

V1 6AG5 RF AMP
V3 6AG5 3RD IF
V7 6AU6 LIMITER
V11B 12S7 CLIPPER
Ok I changed the clipper tube and the b+ came up to Alittle over 100 Vdc and the verticle is good now but I'll try v,1,3,7 I tried others and I already tried v,2,4 6 .

Ok now I tried 1,3,7 , different tubes the only one I got a positive result change from was v1 now the voltage is Alittle over 109 Vdc so that's a big improvement and the verticle is good and solid now so I'll leave it at this point. Thanks for the help guys.

:thmbsp: I'm glad it's working better now.