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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Thu 11, 2018 5:57 pm 
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Ok, I did a leakage check on a few that I could get to with my Solar checker. The few I checked showed no leakage what so ever. I did check a paper cap to be sure the checker was working and it showed plenty of leakage.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Thu 11, 2018 6:22 pm 
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Usually ceramic caps don't have a problem with leakage. The reason I mentioned it is because leakage often makes the capacitance value read too high, so I wondered whether leakage might be responsible for the higher capacitance readings you were seeing. Looks like that is not the case for these, so it should be fine to leave these caps in place.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Thu 11, 2018 6:41 pm 
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Tom Albrecht wrote:
Usually ceramic caps don't have a problem with leakage. The reason I mentioned it is because leakage often makes the capacitance value read too high, so I wondered whether leakage might be responsible for the higher capacitance readings you were seeing. Looks like that is not the case for these, so it should be fine to leave these caps in place.

Tom,
Thanks for the help. I'll leave them alone.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Thu 11, 2018 8:21 pm 
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They are probably within tolerance. A common tolerance range for large value ceramic caps is +80%/-20% . There is a wide range of ceramics used in ceramic caps. Some are used to get caps with a controlled temperature coefficient, which are useful for temperature compensating circuits. Other ceramics are used to get a large value of capacitance in a small package for applications where the exact value is not too important. And there are ceramics that can be used to make caps with tight tolerances and a zero temperature coefficient. Those will be physically large for large value caps but are what is usually used for small caps.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Thu 11, 2018 10:43 pm 
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From the post that I did over on VideoKarma:

"Also, don't forget that you capacitor checker leads could be adding to the value of these capacitors. They are very low in value. Try separating the leads and measure them again.

As Bob mentioned, I would be inclined to leave them alone."

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 12:41 am 
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Yeah guys I left them in. Thanks.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 12:43 am 
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Guys, I've got another problem! Some background first.
all through this recap and recarb, when I powered up the TV, the picture seemed weak. I had to twiddle the Contrast, Brightness, V. Hold, and H. Hold controls just right to get a picture. The picture was always a bit unstable. It would flicker and when I adjusted the Contrast control, the V. Hold would need readjusting. Though I think this might be a nature of the beast. As I went through the recap, the picture got just a little bit better. Then when I was finished with all the recapping, the picture was still a bit unstable but the flickering all but stopped.
Then I changed out the 8 resistors in the tuner. Now here's my problem. I have very good audio but no video. I have a raster but no video. No amount of twiddling the controls will produce a picture. I even tried another CRT with the same results. I replaced the 6AU6 Video Amp tube and even changed 6AL5 Video Detector tube and still no joy. I checked the 2 coils (Sams L14 and L15) or ( Riders, Wallace, and Admiral L9 and L10) and they checked good for continuity.
Could this problem be caused by something in the tuner? I figured that with good audio, the tuner was doing its job.
Any ideas as to where to look?
In the meantime, I'll hook video directly to the Video Amp and see what I get.
Thanks for your help.

Here's a link to the Wallace schematic. Thanks to Phil Nelson.

https://www.dropbox.com/s/vtr06fdq1zs73 ... d.jpg?dl=0

Note: edited to change recapped to change out the resistors.

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Last edited by Crist Rigotti on Jan Sat 13, 2018 7:14 am, edited 2 times in total.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 1:27 am 
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OK, when I hook the video directly to the Video Amp tube, I get decent video.

Then I went back to the original set up and now I'm getting a very faint picture.
I'm thinking that maybe I need to just do the IF/Video alignment.

Can a problem with the tuner cause this problem? Just wondering.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 2:47 am 
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Playing with tuners, even if you don't replace any tuning cap, can ruin
their alignment because of stray capacitance from other parts.

To check for tuner problems a quick check, if you have multiple modulators,
is to try various channels. Its possible to get good sound with bad video
with bad alignment on an intercarrier set like that.

Its probably going to be necessary to at least check alignment,
including the tuner.


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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 3:09 am 
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dtvmcdonald wrote:
Playing with tuners, even if you don't replace any tuning cap, can ruin
their alignment because of stray capacitance from other parts.

To check for tuner problems a quick check, if you have multiple modulators,
is to try various channels. Its possible to get good sound with bad video
with bad alignment on an intercarrier set like that.

Its probably going to be necessary to at least check alignment,
including the tuner.


OK. I planned on doing an alignment as I always do. We'll see if that improves anything.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 3:11 am 
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On the other Forum a member suggested I do a voltage check. I did and here are the results.

There was no signal to the antenna terminals.

Also the "mains" was only at 114VAC. Hence the low voltage on the heaters and B+ was only 237V. When the mains was brought up to house voltage of 124VAC, the heaters went up to 6vac and B+ went to 257V.


Attachments:
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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 5:53 am 
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Why oh why did you recap the tuner? There would have been no paper caps in there. Many places in the tuner rely on carbon composition resistors, they are non inductive, modern carbon and metal film resistors have inductance. You should only replace a resistor in a tuner when you know it to be bad, and 20% off value is not bad. Ceramic caps? Leave them alone, they will be OK and you'll only upset the tuner alignment - which sounds like it has happened.

It looks like you'll need to realign the tuner......


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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 7:12 am 
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irob2345 wrote:
Why oh why did you recap the tuner? There would have been no paper caps in there. Many places in the tuner rely on carbon composition resistors, they are non inductive, modern carbon and metal film resistors have inductance. You should only replace a resistor in a tuner when you know it to be bad, and 20% off value is not bad. Ceramic caps? Leave them alone, they will be OK and you'll only upset the tuner alignment - which sounds like it has happened.

It looks like you'll need to realign the tuner......


I never changed the caps. I just replaced the resistors. Out of the eight resistors 4 were way out of tolerance. The other 4 were close.

I'm sorry I caused some confusion. I edited my earlier post.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 5:43 pm 
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Do you have a video generator that can produce signals at the IF frequency? That's often a very nice way to see if the video IF chain is working properly, and by inference, to show if the tuner is not working properly. Of course, you'll also get a pretty good idea of what's happening when you go through a full alignment, but using the video generator can give you a picture of exactly where the problem is.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 6:01 pm 
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Tom Albrecht wrote:
Do you have a video generator that can produce signals at the IF frequency? That's often a very nice way to see if the video IF chain is working properly, and by inference, to show if the tuner is not working properly. Of course, you'll also get a pretty good idea of what's happening when you go through a full alignment, but using the video generator can give you a picture of exactly where the problem is.


Tom,
I only have a 1077B which I'm not familiar with. Good suggestion though.
I'll go through an alignment today and see what happens.
I went through the tuner last evening in detail. I found no problems. I do have another tuner that is compatible so I'll just "clip lead" in the tuner and try it and then swap out the tuners and try it again. Then go through an alignment.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 8:09 pm 
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I pulled A4 1st IF transformer off the tuner to replaced the 15K resistor. It consists of the 15K resistor, a coil, and 2 mica caps at 10pf and 130pf.

I was expecting some "real" mica caps. Now I'm concerned that those caps could develop silver mica disease. I'm having some real trouble getting a cap reading on each of those with my cap checker. I could cut them in half and install real mica caps.

Here is what it looks like.

What do you think?


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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sat 13, 2018 9:20 pm 
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Yes, that type of mica cap can fail. However, I'd probably wait until trying the alignment or feeding in an IF signal to see whether that transformer is really the problem. Otherwise, you're just making the alignment somewhat more difficult by prematurely replacing these caps. If you find that this transformer can't be tuned properly, then by all means replace those mica wafer caps.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sun 14, 2018 3:06 am 
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Well Late this afternoon I decided to replace the mica caps in A4. I thought that while I had it out, why take the chance. I replaced them with 500V 5% micas. I had the 10pf but didn't have the 130pf so I put 2 in parallel. When I checked them with my cap checker I got 129pf. Good enough. And I also changed out the 15K resistor which read 23K once removed. BTW, all the caps in the tuner were replaced using carbon film caps.

I re-installed the tuner and I now have a much better picture.

On to the alignment.


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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sun 14, 2018 4:06 am 
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That looks pretty decent - so your hunch about the mica wafer in A4 looks like it was correct.

I restored the wood case version of this set 5-10 years ago, and the inside of that transformer looks extremely familiar. So perhaps I also had to rebuild that transformer in the set I restored.

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 Post subject: Re: Scored an Admiral 19A11
PostPosted: Jan Sun 14, 2018 5:29 am 
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Yeah, I guess it was. I just didn't feel good about leaving it like it was.

I try and make sure I post the "oddball" stuff I run into for others behind me. I'm betting some other restorers are thinking maybe that's what's wrong with my set!

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