Admiral 17T1: Never Give Up, Never Surrender

[jr_tech]

Interesting! what do you see on the screen while you make this measurement?

I’m really scratching my head on this one!

jr

[Winky Dink]

On the CRT? Nothing! All the rear controls are set a mid-range. Without more brightness there is nothing on the screen. Most recently, with a lot of adjusting, I could see an oblong blob in which you tell, if you knew what you were looking for, that the TV was trying to show of a test pattern.
Thanks for sticking with me. I'll have to pick this up tomorrow morning.
Winky, "The Eternal Novice"

[Tube TV]

OP can you repost the schematic you're using with this repair so I can follow along? I'm have quite a bit of confusion which schematic we're using.


It would be a good idea to pick up a regular multimeter. Even a cheap harbour freight / hardware store grade one. They deal with some measurements that a DMM is just too sensitive to get proper readings compared to the schematic.

[Winky Dink]

This is the 17A1 schematic from Wallace-Telaides:

https://flic.kr/p/2mv3Wrm

The set I have is a 17T1 chassis. There were relatively few of these made compared to the 19A1 chassis. They're very similar, but the 17T1 has some additional circuits and some production changes. The catch is that the previous restorer probably used a 19A1 schematic. Apparently they knew what they were was doing. It's a sloppy restoration, but it worked when I got it. I'm trying to replicate what the previous restorer did.

Here's another link that may be helpful. It's the 17T1 schematic overlaid on a 19A1 schematic. Printing that's only black (not black with red overprint) indicates a difference between the two chassis.

https://flic.kr/p/2mv7qkt

Thanks for the tip about an analog meter. It never occurred to me that they still made those.

[Winky Dink]

This is 13 seconds of a test pattern video from 09 Jan 2022:

https://flic.kr/p/2mY1fbd

The four following links show one second of the video frame-by-frame. The time between each image is approximately .029 seconds.

Frames 1-9
Adm 17T12 9031 01-09 by H Boyars, on Flickr

Frames 10-18
Adm 17T12 9032 10-18 by H Boyars, on Flickr

Frames 19-27

Adm 17T12 9033 19-27 by H Boyars, on Flickr

Frames 28-36
Adm 17T12 9034 28-36 by H Boyars, on Flickr

[Tube TV]

That is very interesting how it goes from a stretched vertical to a full collapse and back at random like that.

I would be looking with a fine toothed comb in the vertical oscillator circuit.

I'll have to put more thought in on this one.

[old_tv_nut]

I would start with the power supply to the vertical circuit.

[Notimetolooz]

I think, unless you are very lucky and stumble onto something, you are going to have to get some more test equipment.
Many times when something is seen on a TV screen it will give a more definite cause of a problem and a scope will not be necessary. Where the image is distorted in both the horizontal and vertical directions however diagnosis is very hard. A scope would straighten things out rather quickly.
I believe your meter was trying to follow a moving target when looking at the vertical output. An interaction between the measuring cycle of the meter and the vertical signal.
Normal trouble shooting methods would look at the power supply to the suspected circuit stage first, however in this case the power for the vertical output originates in the HV CRT supply (after going through the voltage dividers). You can't measure the HV without a HV probe for your meter.
It looks to me that some supply or something else is cycling up and down over a second or two.

[jr_tech]

Definitely looks like a noisy/erratic power supply problem.

Can you see/hear any evidence of arcing/corona discharge in the HV supply and related components including pots and resistors as well as capacitors?

Is the low voltage supply stable and noise free (audio ok?)

Very nice video and photo work.

jr