Help needed on Admiral 21D1 chassis tv

[Bill Cahill]

Hi. I've got the main thread at ARF, but, I hope someone here can help me.....
I re capped, and, installed all new electrolytics in this 16" deluxe Admiral tv. I checked all resistors, and, replaced open audio output transformer.
Here are the particulars after cleanning up a couple of minor bugs.....

I have 12KV of high voltage.
I have intermittent audio.
Screen barely lights. Very dim. I adjusted the living crud out of ion trap, and, focus coil.
Definately has video problems.

At first, sync, horizontal oscilator, and, vert. were completely stable.
I had great contrast, but, very low brightness.

Now, it has worsenned...
Sound cuts in, and, out on its' own.
On most channels I now have what appears to be a negative picture.
Sync is mostly unstable, now.
Where do I start on this?
Any ideas why my video is so dark?
Picture tube checks good on my BK 465.
Is there a voltage that could be missing, or, a part of the tube that has gone bad, and, still check good?
Brightness control works.
So does contrast control.
How well I don't know, as the picture is so dim....
Power supply voltage is mostly stable.
Slight variations, but, not alot.
At 125 volts I'm getting the proper power supply voltages.
Please help, guys.
Bill Cahill

[init4fun]

Hi Bill ,

Any time I've run into intermittent problems after a total recap , It's always traced back to cruddy tube socket contact with one or more tube's pins . A miswiring wouldn't come and go , so I doubt you've got anything connected wrong , but "fuzzy" tube pin connections can most certainly come and go , especially as the chassis heats during operation .

I wonder also , if the heat applied by the soldering iron when replacing components is enough to bake on some of the more persistent crud , thus making it even harder for the tube's pin(s) to make contact ?

Any potentiometers would probablly be suspect , as well ........

[Eric H]

Bill, is it a glass tube or metal?
If glass is the Dag intact? I've had some sets that didn't work unless the Dag was intact and grounded.

How about a bad or incorrect Ion trap? What happens if you run a magnet around the neck of the tube?

[Bill Cahill]

Metal. 16GP4.
No poor connedtions, dirty sockets, etc. I checked brightness control. Good.
Replaced a bad 100K resistor to that control.
Made slight difference. I now barely see a picture in daylight.
Very dim. Tried a different picture tube. No change.

Tried different ion traps. No change.
I'm getting 12KV hv on bell of picture tube.
Vert. is now stable, but, control is one sided.
Horiz. is stable.
Sync is a little twitchy.
I have good reception.
Bill Cahill

[bandersen]

I restored an Admiral set recently that also had good HV when I measured it at the CRT anode, but had a dim picture. Eventually, I tracked the problem down to a 470K resistor in series with the HV lead that had gone bad. I got erratic values when I tried to measure it. It probably had carbon tracks burned through it. Once replaced, I had a nice bright picture.

That resistor is mounted on the 1B3 rectifier tube base as I recall.
Good luck.

[kvflyer]

Originally Posted by bandersen

I restored an Admiral set recently that also had good HV when I measured it at the CRT anode, but had a dim picture. Eventually, I tracked the problem down to a 470K resistor in series with the HV lead that had gone bad. I got erratic values when I tried to measure it. It probably had carbon tracks burned through it. Once replaced, I had a nice bright picture.

That resistor is mounted on the 1B3 rectifier tube base as I recall.
Good luck.

Could be a good call Bob. When I did my 26R12, I just went ahead and replaced that resistor because I didn't like the way things looked under the socket. I may have avoided a problem by doing that! Resistors are cheap...

[Bill Cahill]

This appears to NOT be the problem with mine..
First, I was getting a steady 12KV on picture tube.

Next, last night, things got alot worse.
At first, after replacing the 6AC7 video amp, which had tested good, I got a rock steady, dark, but, watchable picture. I was monitoring B+.
Suddenly, voltage took a nose dive, and, picture got darker. Then my sync went nuts, and, it developed agc problems. Vert. rolled insanely, and, picture turned completely un wachable. Along with this sound developed a very loud buzz on all channels.
Picture was a twisty, turny mess, and, had also shrunk down to a 4" square in the middle of the screen.
At that point, I could barely see anything at all.
Sound buzz was so loud it drowned out the other sound..
My power supply was slowly going down at this point.
All said, and, done, apparently, something is pulling too much current, and, appears to be either overloading the main power supply, or, the boost.
Not sure what's going on here....
Had to get off to go to church at that time. I will probably try to start checking individual voltages today.
I think I'll start with screen of horizontal output, and, then work over to other circuits.
Something is obviously pulling way too much current.
Bill Cahill

[Bill Cahill]

I think just as a trial, I'll disconnect the one end of horizontal width coil first. That is the coil that had been disconnected by a past tech.
I want to see what that does.
Bill Cahill

[Bill Cahill]

Thanks to my friend, Mr. Detrola, with some hints he gave, and, tw resistors, plus, eliminating a detector short, I am happy to report that I have a bright picture. I have to adjust set yet, but, I do have a bright picture on it....
Bill Cahill