Just finished a recap of an Admiral 20X12. I'll start by saying that the chassis on this thing was REALLY rusty. It sat on a basement floor for God knows how many decades. The only reason I decided to tackle it is, well, I felt sorry for it. You know how it goes :)

Anyway, the Sams for this set leaves a lot to be desired, and here's what I've got.....

No reception, no static, no HV. The horizontal oscillator isn't running, but the vertical is. Okay, so time to start testing resistances. My problem is on pin 4 of the 6BG6. Totally open. It seems that pin 4 is simply a tie point going from the power switch to the transformer.

I checked resistances at the 5U4, and they're in the ballpark, but the moment I put my probe on the tube pin, the resistance will start climbing and climbing until I remove the probe, when the resistance starts to decrease, eventually back to the correct value.

I may be wrong, but I'm starting to put two and two together and think that I may have a bad winding in the transformer. The only other thing that is shown in the Sams that is NOT on the set is a 270K Ohm resistor between the AC line and the transformer.

Whatcha think?

It's possible the 5U4 pin 4 is broken between the pin socket and solder tab. Are you measuring from the top or bottom of chassis? First thing Id do is pull the 5U4 and measure all your power transformer AC secondary voltages referenced to ground, but from the bottom side of the chassis.

I measured topside with an octal test adapter, then confirmed the readings underneath.

I figured that the puzzling resistance measurements had to be an indicator of something which is way off base, but yep, gonna have to start mapping out the B+.

I just realized this is probably like a 20Z1 chassis where the 5U4 sits on top the power transformer cover?

Ayup, it is indeed.

With the 5U4 pulled are you getting around 370vac from pins 4 and 6, ref to chassis ground?

And about 5.3vac across pins 2 and 8?

Does the centertap of the 5U4 HV winding go directly to ground, or does it go thru a resistor chain to ground? If the latter, possibly an open resistor in the chain.
(Maybe post the schematic so everybody can have a look see?)

At any rate I don't understand how your vertical oscillator could be running if there were something wrong with your transformers high voltage winding.

You can verify your supplies by checking dc voltages on pins 1,6,7 of V11. Also pin 5 on V14

Yes the high voltage center tap goes to ground.

Schematic here.
http://www.earlytelevision.org/pdf/Admiral_20X1_Sams_100-1.pdf

At any rate I don't understand how your vertical oscillator could be running if there were something wrong with your transformers high voltage winding.

Neither can I, but I can hear it faintly running and changing in frequency with the control.

It is possible that climbing resistance is your meter's resistance test charging up a capacitor.

It is possible that climbing resistance is your meter's resistance test charging up a capacitor.

You're right. I guess I too often assume that people have that understanding when they're measuring across caps in circuit. And more than likely Sams assumes that you're measuring with something like a Simson 260, which charges caps faster than a modern DVM.

With the 5U4 pulled are you getting around 370vac from pins 4 and 6, ref to chassis ground?

And about 5.3vac across pins 2 and 8?

Roger on both counts.

Sounds like the power transformer is fine. How about voltages on that V11 audio output tube? Have any hum/ buzz when you touch it's grid, or the center tap of the volume control?

Well, interestingly enough, I now have static in the sound. No reception (no matter how I turned the contrast), but definitely static.

The 6AS5 is used as a B+ dropper in lieu of a big fat resistor. There should be well over a hundred volts at the cathode (pin 1).
The tube voltage chart says 0V. on pin 1, which is flat out wrong. Typical Sams screwup.

What's the voltage on the plate (pin 7) and screen grid (pin 6)? The chart voltages look 'waay too low here, too.

Sams has a note that shows pins 1,2,5,6,7 are all measured from pin 1 of V11. Which is why they show 0 volts on pin 1. Also why the the other voltages seem low. I'm not sure why they don't want to reference ground on those measurements.

FWIW, have you checked the 1/4 amp fuse in the fly cage?

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?

Sams has a note that shows pins 1,2,5,6,7 are all measured from pin 1 of V11. Which is why they show 0 volts on pin 1. Also why the the other voltages seem low. I'm not sure why they don't want to reference ground on those measurements.

FWIW, have you checked the 1/4 amp fuse in the fly cage?

First thing I did. I'll scope out the 6AS5 in the morning.

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?
Hyup. I shoulda reddit closer.

:deal:

Everyone's starting to talk like Sandy around here. :D

And WHAT'S wrong w/THAT ?!? (grin) Tim, sorry yr having such TROUBLE w/this Bad Boy... I always thought these Admirals were sposed to be "Easy-Peasy" sets. Guess I was Wrong. By the Bye, I'm told that I DON'T have too bad of an accent. I DID "Cheat" a bit, & cranked it up to 11, when I went up to meet LA's family in Cape Cod.. THEY were Damyankees from the very Heart of Damyankeeland. I was rather scared they would chew me up, & spit me out..Surprise-They were LOVELY people, & couldn't have been any nicer. But I DID drop an awful lot of "Yes, Ma'ams/No Ma'ams/Yes, Sirs/No Sirs" just in case. 2 of LA's aunts/cousins said you NEVER hear that up there any more.. I told 'em that I DIDN'T want the ghosts of one or BOTH of my Southern grannies rising from the grave to jerk a Knot in my tail because I'd forgotten how to treat a lady.. They grinned at that... Little did they know I was about half SERIOUS...

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?

Assuming Pin 2-5 means 2 and 5, not 2 through 5 :) , everything is spot on.

Once you get the Uv running if you get no reception check the rf chokes. Ive had a couple admirals and a choke was open. The fly is ok?

Assuming Pin 2-5 means 2 and 5, not 2 through 5 :) , everything is spot on.

Correct

Lets check your dc voltage across C1, section C(20 MFD) - just to make sure your focus coil isn't open. Whatever that measures, you should have the same voltage on either side of the 1/4 amp fuse in the fly cage.

Yep, we're looking good there. What's next?

So what voltage did you measure on C1, section C? What dc voltages do you measure on pins 2 and 5 of the 6SN7 horizontal oscillator tube?

Measuring 438V on C1 and on pin 5 of the 6SN7. Pin 2, I got nuthin. Ahaaaa.....that gives me some direction.

Did you mean 338v on C1 sec C? 438 seems too high based on your other measurements.

Positive. C1C is at 438V.

The B+ is 'waay too high, suggesting there's insufficient load to pull it down to spec. Likely the H.output stage is not conducting.
There's B+ on both sides of the fuse, right?
Since The damper is in series in the B+ pathway to the H.out stage, an open damper would cause your problem. Have you subbed the damper?

If so, with the set off, check for continuity from the fuse to pin 5 (plate) of the damper. Should be about 11 ohms.
Then check from pin 3 (cathode) of the damper to the plate of the H.out tube. Should be around 165 ohms.

So what voltage did you measure on C1, section C? What dc voltages do you measure on pins 2 and 5 of the 6SN7 horizontal oscillator tube?

First, I screwed up here and somehow measured voltages on the correct cap, but the wrong tube :tears:

Let's revise this one. Pin 2 has -30VDC, pin 5 has nothing.

The B+ is 'waay too high, suggesting there's insufficient load to pull it down to spec. Likely the H.output stage is not conducting.
There's B+ on both sides of the fuse, right?
Since The damper is in series in the B+ pathway to the H.out stage, an open damper would cause your problem. Have you subbed the damper?

If so, with the set off, check for continuity from the fuse to pin 5 (plate) of the damper. Should be about 11 ohms.
Then check from pin 3 (cathode) of the damper to the plate of the H.out tube. Should be around 165 ohms.

B+ on both sides of the fuse, yes. Subbed the damper, both tubes tested good (both original and replacement), no changes.

continuity from the fuse to pin 5 (plate) of the damper. Should be about 11 ohms. Spot on.

Then check from pin 3 (cathode) of the damper to the plate of the H.out tube. Should be around 165 ohms. Zero.

Then check from pin 3 (cathode) of the damper to the plate of the H.out tube. Should be around 165 ohms. Zero.

Zero is very bad. Sounds like your flyback may have a shorted primary, although it seems unlikely that it would form a dead short? Possibly there's a wiring error? Try measuring directly across pins 1 and 2 of the fly transformer, there should be like 185 ohms.

Also you need to find out why there's no B+ getting to pin 5 of the horz osc tube. You should measure something like 75,070 ohms from the fuse to the 6SN7plate(pin 5).

Here's the horizontal section from my Admiral schematic. Easier to follow than the Sams, plus it has the voltages and resistances marked on it.

http://i452.photobucket.com/albums/qq245/Kuehn/VK%20Pictures/Admiral%2020Z1_zpstvpvazop.jpg

Zero is very bad. Sounds like your flyback may have a shorted primary, although it seems unlikely that it would form a dead short?
By "zero" he probably means 'open'. There's also the H.linearity coil in series between the damper cathode and fly primary. The H.lin coil could be open.

By "zero" he probably means 'open'. There's also the H.linearity coil in series between the damper cathode and fly primary. The H.lin coil could be open.

You nailed that one. Sams shows it should read 36 ohms. Totally open. I think I have one from a parts chassis I can scrounge later.

The 6AS5 is used as a B+ dropper in lieu of a big fat resistor.

It's a sensible way to drop the B+, putting the otherwise wasted power to work. Cuts waste heat, and lessens the load on the power supply.

By "zero" he probably means 'open'. There's also the H.linearity coil in series between the damper cathode and fly primary. The H.lin coil could be open.

Oops, my bad. I always think infinity, but I should have read it in context of too high of B+.

It's a sensible way to drop the B+, putting the otherwise wasted power to work. Cuts waste heat, and lessens the load on the power supply.

Apparently it regulates well too.

Well, I nabbed a linearity coil out of a GE 810 chassis that I had here. It read 30 ohms versus the 36 in the Sams, but I figured that would get me a lot closer than an open coil would.

Sure enough, the horizontal oscillator started to run, and I got nice HV to the plate cap of the 1X2 :)

No HV to the picture tube yet, but all that's left in that chain is a 1 meg resistor and a door knob cap.....both of which I should have in stock. Time for some more testing!! :)

Good goin' bro. Still kinda curious why there was no plate voltage on the H.osc before.:headscratMaybe there was a production change so it runs offa Boost instead of B+ (?)

Equally curious how the vertical Osc. was running before, with no boost.

Not sure, but I could hear it, and the frequency did change with the vertical hold.

Doorknob cap is fine, as is the 470 MOhm resistor on the 1X2 (Sams shows it to be a 1 Meg, but....anyway). Next, I'll clean the snot out of the tube pins and tube socket.

Not sure, but I could hear it, and the frequency did change with the vertical hold.

I guess Sams does show that some version had the V Osc. running off of B+. They show the alternative path with a dotted line.

Doorknob cap is fine, as is the 470 MOhm resistor on the 1X2 (Sams shows it to be a 1 Meg, but....anyway). Next, I'll clean the snot out of the tube pins and tube socket.

470 M, as in mega ohms? Or is that the really really ancient abbreviation for one thousand? ;)

470K. I typed it too fast :drool:

But hey! I gots a raster!!!! :yippy:

I can barely get any sound at all on frequency and it looks like the IF's gonna need work, but this is a major leap forward, thanks to you guys!!!

Now, next question....source an Admiral replacement for that linearity coil, I assume?

Sweet!

I can cross that Lin coil to a Thordarson. But something tells me they were all pretty generic from the period.

Thordarson WC-14.

http://www.ebay.com/itm/Thordarson-WC-14-horizontal-Linearity-Control-Meissner-new-old-stock-in-box-/221962682864?hash=item33ae01c1f0:g:DAIAAOSw8-tWZhH1

Hopefully the filter caps had enuff headroom for that sustained high B+.

Hopefully the filter caps had enuff headroom for that sustained high B+.

Just enough. I went 450 across the board....

Thordarson WC-14.

http://www.ebay.com/itm/Thordarson-WC-14-horizontal-Linearity-Control-Meissner-new-old-stock-in-box-/221962682864?hash=item33ae01c1f0:g:DAIAAOSw8-tWZhH1

Mine! :D Thank youuuuuu!

Well, the coil's in. Hm.

Very weak signal, very little contrast. In fact, I may have tweaked something in the wrong direction, as now when you turn up the contrast, the picture goes negative....

Any chance you could post a vid of what it's doing? That horiz breakup suggests one (or both) of the slugs in the H.freq. can (L17) might have been futzed with.

It's really hard to show. When I installed the new coil, I set the frequency as I usually do when it's off on a first powerup.....keep turning....4 horizontal images, 3 images, 2 images, boom.....done. In this case I got it as close as I could, but the image on screen is so washed out that I can't get a clear shot of it. This is what it looks like with no signal. With really weak sound and picture when it has a signal, this to me shows an AGC problem, first and foremost....unless I'm wrong :)

Do you have a scope to check the H osc. wave shape? The raster pic from your previous post makes me think the other slug that sets wave shape is miss-adjusted.

This may sound wacky, but I tend to adjust synchroguide oscillators with a scope. First I scope a composite video source and get 2 sync pulses on the screen as a reference H sweep time, then I adjust the synchroguide to match that time and adjust the peak and mound to about the same height....Might be over kill, but in early color sets with that circuit it helps me feel confident about the H sweep system.

Doesn't sound wacky, it sounds very educated. Far more so than I am, I'm afraid.

Don't own a scope, don't know how to use one, don't know what I'm looking at even if I did. I'm a heck of a TV mechanic, but as a technician I leave a lot to be desired :)

But that would have no effect on the AGC anyway, would it? Obviously the issue's still gonna be there, but I can't get enough gain to really get much on the screen as it is.

If it uses keyed AGC (I'm not familiar enough with this chassis to say) horizontal issues will affect the AGC....If it's just regular AGC the two are more autonomous.

No keyed AGC. Uses a 6AL5 dual diode as video det/AGC. One diode detects video, the other is for AGC. If I recall correctly, I think there's like a 1.5v delay on AGC line.

So, after replacing a resistor outlined in this thread:

http://www.videokarma.org/showthread.php?t=265914

This is what I've got.

Width control does nothing. There are only two out of the three terminals used on the contrast control, and it looked as if someone did some soldering there. Then I figured it out.....

The contrast control has a dead spot on the far clockwise position, and now that I've got that resistor replaced and the contrast control actually does something, I realized that someone along the way wired in the contrast control backwards so that the counterclockwise position is maximum gain......

By adjusting the horizontal frequency, this is as close to a single image that I've managed to achieve.

Looks like the H.osc frequency is running 'waay high and locking to an integer of 15,750 Khz.

Looks like the H.osc frequency is running 'waay high ...

Looks to me it's locking onto 1 1/3 times the proper horizontal frequency. Maybe a frequency setting coil in the oscillator section is too far out of adjustment?

The bottom of the horizontal oscillator's just a mess. Here's a shot of that, and another shot of the section. The orange drop was done by the last person that worked on it, I should probably change it out just because......

If the osc. coil is out of range I'd check the resistors and try replacing that orange drop...If that fails see if adjusting the other slug of the osc. can gets you anywhere.

Have you tried adjusting the horiz. range trimmer, designated B2 in Sams? It's located on the rear chassis apron, next to the horiz. drive trimmer (just to the left of it).
Also there's two resistors, R75 and R76 (68K and 120K respectively), coming off either end of the horiz. hold control. Either of those being off value will affect the range.

What value is printed on the Orangedrop cap? Is it .002 mf?

I didn't try the range because I was assuming that it was a frequency issue.....can't hurt though :)

The orange drop was a .002. I changed them both, no change in performance. I'll check the resistors tomorrow. I'll get back on the 8TS30 as well :)

I didn't try the range because I was assuming that it was a frequency issue.....can't hurt though :)
It means `frequency range`, like a coarse adjustment, with the H.hold being the 'fine adjustment'.

It looks as though sumbody was working on this problem at length, then gave up on it when that Lin coil blew.

Well, I've spent time over the last couple weeks on this set and got basically nowhere. This morning I got up at about 3:30 AM after falling asleep at about 8:30 PM last night, I had a full head of steam and decided to tackle this set, do or die.

I disasembled and tested everything in the entire horizontal circuit, found one missing cap on the width coil (this set was pretty botched up before I got it), and no change. After testing about a dozen resistors and replacing a couple that were way out of tolerance, still no change.

Then I noticed a couple green spots of corrosion on the back side of the width coil, where I couldn't have seen them before. Looks like a couple turns are shorted....which would explain why the turning the width coil does absolutely nothing. That, and the fact that the horizontal lin coil, which sits right below it, was corroded and open, leads me to believe I need a width coil. Spec on the Sams is .1 ohms, this one reads about 1.3 ohms.

I'll pick this up after I get one......

Good luck with it. Sometimes you get those sets that just play flawless with a re-cap and others have all sorts of issues. I guess it's the conditions they were stored in that determines that.

When you're talking 1.2 ohms error, make sure your meter was able to zero first, and that the terminals on the coil are clean(maybe re-solder them) It doesn't take much contact resistance and you end up with a false reading.

Even when working correctly, the width coil has very little effect. From one extreme to the other it will change the width maybe an inch or even less. The with coil is in parallel with the flyback coil and used to tweak it's characteristics.

BTW that photo you posted earlier of the bottom of the hor. osc. circuit is stock. Admiral made really wired it that way with three resistors connecting together in mid-air.

Yep, I figured that out by the schematic. As I said, I tested every resistor in that entire string. Since the width control does nothing and I have inadequate width, along with the resistance of the coil, I figured that would be the next step. Terminals were definitely clean, as I de-soldered and cleaned the ends of the wires to the coil.

These sets are never this difficult! :)

Welp, she's working great now!

The problem turned out to be a simple one. Whoever was futzing around under the 6BG6 (probably before I was born), cut a cap out of it that I couldn't even see. Looks like someone back then was testing things and just gave up. That, and the width coil out of a parts set (thanks bgadow!) brought the set back to life! :)

Horizontal lin's a little off, but I'll play with that after a little usage.

And finally, another tough dog is done. Whew.

Well done Tim!!! Perseverance! !!

Kudos to you Sir. Good job! :rockon: Of course I'm curious which cap it wuz.

It was a .2 uF 200V cap anchored to a dead pin on the 6BG6 going to the ground on the filter can closest to the tube......