Working on an Admiral 20X12

[Kevin Kuehn]

Sweet!

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

[Kevin Kuehn]

Thordarson WC-14.

http://www.ebay.com/itm/Thordarson-W...IAAOSw8-tWZhH1

[old_coot88]

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

[Kamakiri]

Originally Posted by old_coot88

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

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

[Kamakiri]

Originally Posted by Kevin Kuehn

Thordarson WC-14.

http://www.ebay.com/itm/Thordarson-W...IAAOSw8-tWZhH1

Mine! Thank youuuuuu!

[Kamakiri]

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....

[old_coot88]

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.

[Kamakiri]

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

[Electronic M]

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.

[Kamakiri]

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.

[Electronic M]

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.

[Kevin Kuehn]

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.

[Kamakiri]

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.

[old_coot88]

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

[wa2ise]

Originally Posted by old_coot88

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?