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 Post subject: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 5:35 pm 
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Hello, forum members.

After a long hesitation, I have decided to try and tackle the 20B1 chassis for my Admiral 24C16 (CRT tested good).
Oh, my... I am afraid that I bit w-a-a-a-a-y more than I can chew, but maybe with the help of much more knowledgeable folks here I will manage to bring it back to life...

So, at a first glance, it's a bit overwhelming for a newbie. I am starting from a 6AL5 "Ratio Detector" - this is where I see an evidence of a previous attempt at repair.

Well, this one is a bit of a mess - an electrolytic cap has been "replaced" with an in-line version - wrong voltage, wrong capacitance. Mica cap has been cut on one end, so I guess this "repair" did not get too far...

Attachment:
V11_6AL5_OLD.jpg
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Now, let's see if I can make some sense of what's going on here:

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V11_6AL5-1.jpg
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My "cleanup" attempt - re-located the e-cap to the socket, re-routed a new mica cap, changed resistors (some drifted way off, so I have opted for a "shotgun" replacement).

Attachment:
V11_6AL5_NEW.jpg
V11_6AL5_NEW.jpg [ 901.61 KiB | Viewed 3382 times ]


This is my first go at a TV resto, so - any thoughts? Suggestions? Tips?


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 6:10 pm 
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Location: Lafayette, CO
You will need to power that up at some point. Before you do, pull the rectifier to verify the power transformer isn't fried. Measure across the B+ to B- ......should be above 1000ohms. Go full monty and watch the 5U4. Filament glow is good, plate glowing orange or blue flashes means you troubleshoot. Magic smoke means you troubleshoot. Your wiring is tidier than mine but l don't replace so much. Craig


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 6:28 pm 
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On that wrong voltage and wrong capacitance cap, the voltage only has to be high enough and the capacitance only has to be high enough. But if the capacitance is way high there could be strange effects with variations in the signal strength of the received signal. That said, using values close to the original values is the way to go.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 7:05 pm 
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Tom Schulz wrote:
On that wrong voltage and wrong capacitance cap, the voltage only has to be high enough and the capacitance only has to be high enough. But if the capacitance is way high there could be strange effects with variations in the signal strength of the received signal. That said, using values close to the original values is the way to go.


Good point, and I do try and follow this rule. The cap that was spliced in though was way off on both counts - 10 uF @ 25 VDC, whereas the manual calls for a 4 uF @ 50 VDC (verified against the stamping on the can itself). I have put in 4.7 uF @ 50 VDC (the small black cap with green shrink tubes between pins 5 (+) and 4 (-) of the socket).


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 8:12 pm 
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For what it's worth, this article describes how I restored my Admiral 24C15 with 20B1 chassis:

https://antiqueradio.org/Admiral24C15Television.htm

That is some tidy-looking work that you have done so far. As analog.tv notes, you will need to power it up sometime, and I would say, the sooner the better.

If you can get the TV working in some fashion soon, that will make it MUCH easier to confirm that you are staying on the right track (i.e., not making mistakes) while you replace more capacitors & whatnot.

The risk of shotgunning many components "blind" is that even a tiny mis-wiring may create a problem that is hard to diagnose later on. (Standard debugging techniques don't account for the possibility that someone might have accidentally mis-attached the wrist bone to the knee bone!)

If the TV is working somewhat, you can test it briefly after replacing each one or two components. Then, if a weird problem suddenly arises, you only have to double-check one step instead of dozens.

Anyway, enjoy your project. Take your time and check off each new component on the schematic & parts list as it is replaced. Combine that with the "retry as you go" policy, and the whole process may seem less daunting.

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Fri 29, 2021 11:02 pm 
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Location: New Hampshire
First your work is great. Graphics are also awesome.

Phil gives great advice. So many sets never get fixed up because the owner got carried away.
My personal advice has been:
1) get the power supply safely running.
2) get the hoz / HV up & running to get a raster. At this point you can evaluate things for real like the CRT
3) repair stage by stage. Dont recap now. Trouble shoot first.
4) recap stage by stage checking the set every few caps. DONT change disc caps unless you know they are bad.
5) NEVER tweak any coils except the hoz osc. Some others can be tweaked when you learn how.

These 10" tall Admirals were great sets & a good intro. Right after the war my father bought one & it was
the 2nd set in town ( the dealers was the 1st). He traded it for a bigger Zenith abt 1952. Before my time !!

73 Zeno 8)
LFOD !


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Sat 30, 2021 2:11 am 
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zeno wrote:
First your work is great. Graphics are also awesome.

1) get the power supply safely running.
2) get the hoz / HV up & running to get a raster. At this point you can evaluate things for real like the CRT
3) repair stage by stage. Dont recap now. Trouble shoot first.
4) recap stage by stage checking the set every few caps. DONT change disc caps unless you know they are bad.
5) NEVER tweak any coils except the hoz osc. Some others can be tweaked when you learn how.


Thank you, in this case I will turn my attention to the power chassis. Since this is my first set, some trivial questions:

1) Will re-cap the PS chassis, shouldn't be too hard (famous last words). Did a quick check of the secondary windings - between Pins 4 & 6 of 5U4G it's 80 Ohm, between Pins 3 and 5 of 6X5 - 126 Ohm.. Does this sound about right? Also - is there a way to check just the PS chassis after the recap, without connecting the CRT yet?
Attachment:
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2) Assuming that ALL tubes will have to be in to test the HV, including 1B3 correct? No way for me to get the raster without it?
3) Wouldn't old leaky e-caps potentially cause some damage if set is powered up? Just want to make sure that I can do that without releasing the magic smoke...
4) Do not intend to change disc caps or Mica ones that are part of LC assemblies. Exception - plan on changing the "bare" ones in the audio transformers at the last stage, 30 and 35 pf (if I even get that far, that is)
5) Will not touch the coils - at this stage this is well beyond my skill level


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Sat 30, 2021 6:34 pm 
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Location: Dallas, TX
One hand thing about tube based electronics is that you can pull tubes to isolate sections.
For instance, you can remove the power supply rectifier tubes V515 and V516 and check some items.
This would be a good time to use a dim-bulb tester if you have one, or a variac and current meter.
The other tube filaments would still be connected so there will be some current being drawn but not much will be risked.
You can then apply power without the dim-bulb and check the secondary voltages and see if the power transformer overheats. One thing the transformer resistance cannot detect is a shorted turn, that would cause excessive current to be drawn and the transformer to overheat. All the tube filaments still in the set except the HV rectifier should glow.
If that all looks OK, then you could go one to replacing the power supply electrolytic filter caps.
After the filter caps are replaced you can re-install the power rectifiers, apply power carefully and check the DC supply voltages and raster, etc.

I'm all for neatness and the insulating sleeving is a good idea, however when you work on the tuner and IF section you should route the component leads and lengths as near as original as possible. Changing as little as a quarter of an inch to the lead length in those areas could mean you should do an alignment.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Jan Sat 30, 2021 7:25 pm 
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Fennec wrote:
1) Will re-cap the PS chassis, shouldn't be too hard (famous last words). Did a quick check of the secondary windings - between Pins 4 & 6 of 5U4G it's 80 Ohm, between Pins 3 and 5 of 6X5 - 126 Ohm.. Does this sound about right? Also - is there a way to check just the PS chassis after the recap, without connecting the CRT yet?
2) Assuming that ALL tubes will have to be in to test the HV, including 1B3 correct? No way for me to get the raster without it?
3) Wouldn't old leaky e-caps potentially cause some damage if set is powered up? Just want to make sure that I can do that without releasing the magic smoke...
4) Do not intend to change disc caps or Mica ones that are part of LC assemblies. Exception - plan on changing the "bare" ones in the audio transformers at the last stage, 30 and 35 pf (if I even get that far, that is)
5) Will not touch the coils - at this stage this is well beyond my skill level

1) The advice in the previous post is good advice. Those resistances sound about right.
2) To get high voltage you would need the horizontal oscillator, the horizontal output, the damper and the high voltage rectifier (1B3). But without vertical deflection you would get a thin horizontal line on the CRT which could be bright enough to burn the phosphor on the CRT unless you have the brightness turned way down. To get a raster you would also need the vertical oscillator and vertical output.
3) Leaky electrolytics can cause damage, especially if they short. If you are quick to disconnect the power if you see the rectifier tubes arc and flash then the damage would be only to those tubes. If you are a little slow then you could damage the power transformer. A dim bulb tester as mentioned above would prevent damaging the transformer.
4) If those bare ones are associated with a coil or transformer winding then they are part of a tuned circuit. Replacing them would require aligning those circuits as the replacements would not be exactly the same value as the originals due to tolerances.

As tor troubleshooting before replacing the paper caps. If a circuit is dead then troubleshoot. But if you have a problem like bad vertical linearity, incorrect height or you can't sync the vertical with the vertical hold control, don't troubleshoot first. Replace the paper and electrolytic caps in the vertical circuits first as they are all bad and most likely are the cause of the problems.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Mar Tue 02, 2021 3:39 pm 
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The project is stop-and-go at the moment, but I have managed to re-cap the PS chassis. Not too bad inside there, cleaned up the wiring a bit, replaced the speaker leads, giving myself an ability to unplug the speaker should a need arise without removing it from the cabinet. There were just enough free terminals on the existing boards for me to mount the new electrolytics.
Attachment:
PS-after.jpg
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Back to the main 20B1... Well, started good, replaced C4A (20uF) and C4C (50uF) - in Sam's notation - e-caps, decided to change a drifted resistor or two, while I am in there... And finished up cleaning-up an entire R1-R2-R3 section. I must have an OCD or something...

While doing a cleanup, decided to add a retrace blanking circuit - credit and thanks go to Phil Nelson here. I hope that I did not connect a shin bone to a wrist bone or something by accident :)
Attachment:
R1-R2-R3-after.jpg
R1-R2-R3-after.jpg [ 490.69 KiB | Viewed 3078 times ]


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 15, 2021 7:38 pm 
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OK, gentlemen - it took me a while, but recapping (except mica and ceramics in LC circuits) and resistor replacement (almost all, save for IF strip and half a dozen of those I couldn't easily get to) is complete.

Powered it up today. The result is as follows:

- There is raster
- There is crackling from the speaker

Back adjustments:

Horizontal drive - responsive
Horizontal lock - responsive
Height - responsive
Vert. linearity - responsive

(Horizontal linearity and Width did not check yet)

Front controls:

All responsive (insofar as the changes in how the raster looks, volume changes as well)

Now for the bad news - I am getting no sound and no picture from the source (DVD through an RF modulator and a balanced line adapter).

This is all I am getting on the screen (Ch 4):

Attachment:
IMG_20210815_135134169.jpg
IMG_20210815_135134169.jpg [ 396.23 KiB | Viewed 2394 times ]


Since this is my first attempt at a TV resto - is what I am getting (or rather not getting) really bad? Or is it something that I can attempt to fix myself? Where should I start looking?

At this point I would need all the help I can get in pinpointing the possible source of the issue, and any advise would be greatly appreciated.


Last edited by Fennec on Aug Sun 15, 2021 8:49 pm, edited 2 times in total.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 15, 2021 8:24 pm 
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Before diving too deep, let's check a couple of obvious things about your setup.

1. Using the same video source (DVD, etc.) connected to a different TV, does that TV produce normal picture and sound?

2. Is there a different video source (an old VCR, alternate DVD player, etc.) that you can connect to this TV, and if so, what's the result?

Phil Nelson

P.S. It looks like you're pretty close!


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 15, 2021 8:34 pm 
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I'm sure you can get it working from this point.
Good point is that you have H.V for the CRT and you have enough width (horizontal sweep). The horizontal sweep frequency is off, probably the on chassis adjustment of the horizontal frequency range need to be checked. I think it is a horizontal lock coil.
There isn't enough height. You might want to compare voltages around the vertical section to those in the service data.
Just take it a step at a time.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 15, 2021 10:11 pm 
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A quick update - rotating the Horizontal Linearity and Width adjustments on the back does not produce any visible effect on the raster... Not even a flicker... This can't be good, I think - even with no detectable input signal I should be able to see some effect, at least insofar as the width is concerned...

Having said that - is there a way to inject the signal directly into the Video and Audio amplifiers through the alligator clips? One would assume that audio can be fed into the input of the volume control (?), and video into the grid of a video amplifier (6AC7, V7 in Sam's nomenclature), but the problems with the Horizontal Linearity and Width likely will remain - I just want to check if at least part of the circuit is operational...


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Mon 16, 2021 1:42 am 
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Don't be concerned about the width and linearity adjustments. They have a very subtle affect.

As Notimetolooz said, your horizontal lock is off. There's an adjustment for it on the back of the set.

This model has a "double D" mask so the image should fill all the way to the rounded sides, but not fill vertically. Looks about right as it is.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Mon 16, 2021 5:51 am 
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You are very close.

Adjust the Horizontal Hold (or maybe it's called Horizontal Lock) in the direction that makes the lines get broader. Keep going and the picture will lock in.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Mon 16, 2021 3:15 pm 
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bandersen wrote:

This model has a "double D" mask so the image should fill all the way to the rounded sides, but not fill vertically. Looks about right as it is.

Right, I forgot about that.
You want to get a good raster on the screen, either blank or with snow, at this point. Since the horizontal frequency is off the sweep isn't working at the right conditions for things like width and linearity to have the correct effect.

Can we assume that you tested all the tubes by now?
It isn't uncommon to find one or two tubes bad. Overall many times I have found about 20% of tubes to be weak but still functional enough to still use.

As far as doing something to prove some other section are working, you can touch the center terminal of the volume pot with a screwdriver and see if the audio section is OK. On this set it looks like there is a cable connection for the audio so you could plug another sound source into the jack.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Mon 16, 2021 10:59 pm 
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Notimetolooz wrote:
Can we assume that you tested all the tubes by now?
If you don't have a tube tester, this article explains a very simple dud/not-dud test that you can do with an ohmmeter:

https://antiqueradio.org/FirstStepsInRestoration.htm

That test only tells you if a tube is totally dead (i.e., it has a burned-out filament), not whether it is "strong" or "weak." However, even a weak tube will often work well enough for you to complete the basic restoration, so if you do use a tube tester, don't automatically throw away every tube that doesn't look perfect. Tube testers are approximate devices at best; the only true tester of a tube is the TV itself.

While you're checking tubes, I recommend cleaning all the tube pins and sockets, as described in the above article. Also clean the potentiometers used as volume controls and the like.

Do the testing/cleaning of each tube and its socket one tube at a time, to avoid mixing up the tubes.

In a case where your video and audio circuits are working normally (or close), but you have a no-signal condition, the TV's tuner is another place to look. Cleaning a tuner is not as simple as cleaning a tube socket, however. Near the beginning of this thread is some excellent advice about tuner cleaning from Mr. Detrola of this forum:

https://www.antiqueradios.com/forums/vi ... p?t=113296

Before tackling the tuner, perhaps you could tell us what you see when you turn the channel selector to different channels. Do you see snow on the other channels? A clear blank (but lit) screen? Something else?

What do you see (and hear) during the momentary break when you switch from Channel X to Channel Y? Audible static? Visible flashing on the screen? Something else? Nothing?

For that matter, what do you see when you select Channel 4 with your signal, and then remove the signal? What happens if you switch your source (and channel selector) to Channel 3 instead of 4?

Again, it looks like you're only a few tweaks away from a working TV, so let's hope the rest of your project goes smoothly.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Tue 17, 2021 11:28 am 
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Hey don't over-complicate it, guys!

No need (yet) to test tubes, we have a signal already getting from the antenna terminals to the screen. So they are all working.

As I used to drill into my TV tech apprentices back in the day:
1. Think with your head, not with your hands.
2. Touch as little as possible.
3. Look and learn, measure, collect evidence.

A tweak of the horizontal hold WILL get you a picture. What it looks like will determine what you do next.

The fact that it already works as well as it does tells me that it's already had at least a partial recap some time in the past.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Tue 17, 2021 8:26 pm 
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OK, gents - a couple of clarifications:

1. All the tubes have been tested, and found to be well into the "green" range. I had to replace two - the 1B3 HV 1/2-wave rectifier, and a 6J6 converter. I have also tested mutual conductance, and all of the tubes are very strong, with no shorts.

2. Entire set has been completely re-capped (electrolytics and PIO), and most all resistors have been changed by yours truly. As a side note, quite a few in the Horizontal circuit have drifted so high as to be 2x the nominal value (??)

3. After fiddling for a while with "Horizontal Lock" and "Horizontal Drive" controls in the back, I had a brief and small measure of success in getting some semblance of an image (still no sound):

Attachment:
IMG_20210817_140017305.jpg
IMG_20210817_140017305.jpg [ 472.39 KiB | Viewed 2263 times ]


However an attempt to further improve the picture by adjusting "Horizontal" and "Vertical" controls on the front of the TV has made things considerably worse, and I was unable to replicate a stable picture from just a few minutes ago :( - this is the best I was able to achieve so far (again - no sound):

Attachment:
IMG_20210817_142732990.jpg
IMG_20210817_142732990.jpg [ 620.68 KiB | Viewed 2263 times ]


It appears that I can't stabilize and lock the correct horizontal frequency at the very least... Adjustments are very touchy. The picture seems to be significantly shifted to the left (appears to be shifted to the right, because I am using the mirror) and also ghosting vertically... Proportions are obviously out of whack, but this can wait...

That said - I suppose that the first priority is to try and get a however distorted but rock solid and stable picture. What do I need to check for that? A bad tube? Unbalanced resistors? A bad mica cap somewhere in the LC circuit?


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