Admiral 21F1 HV issues

[zenith2134]

Hello.

I have a very nice 21F1 chassis with good cabinet and crt but no HV. The 1B3 doesn't even light. I have swapped out the damper, horizontal tubes, and 1b3 to no avail. The previous owner did extensive recap work to the underside and I doublechecked all of those connections which are all good. (In fact, it was a very clean job!)

Next I'm going to swap out the HV transformer since I have an identical 21F1 with no vertical sweep. (needs re-capping).

The service manual only suggests which tubes could cause this, and I changed those out already. Anyone have a set with this chassis?

[Eric H]

If your HV transformer looks OK it probably is, the 1B3 doesn't light enough to easily see
I'd look for a problem in the Horiz Oscillator circuit, check the voltages on that tube and if it hasn't been recapped in that area that would be a good place to start.

Does the set have sound? If it's totally dead it might be a problem with the low voltage supply.

I hate to say it but often times problems are caused by someone mis-wiring a cap when they recap.

Do you have a schematic for the set?

[zenith2134]

Hi Eric. Yes I have the schematics, thank goodness. Guess I'll have to dig in. The 1b3 glow is barely visible on the other chassis like you said, but on this one, nada, even with the lights in the room (garage) out.

The set has clear sound and tuning, and I hear the horizontal come up also. I'm going to test the transformers for open circuit next, then I don't know. I guess it'd be a waste to swap flybacks, huh?

[bgadow]

I would, if you haven't already, do the neon or cfl light test. Are you familiar? (these type of bulbs will glow if held near HV AC)

If the horiz osc is running but on the wrong frequency you might not get HV.

The other simple thing: if it uses an ion trap, try moving it around. Granted, you didn't ask dumb questions-but these may be dumb answers I gave!

[zenith2134]

Not dumb at all, thanks for the help!

I did the CFL test like Eric H. described in the earlier thread. Nothing at all on the suspect chassis; lit like a champ on the other.

I'm going to check the horiz oscillator frequency next, good idea.

Would improper ion trap setting cause no HV? I didn't think i would but what do I know?

[bgadow]

The trap wouldn't kill the HV-I mentioned it because I have had sets before where there was HV but no raster-and I kept blaming it on the HV.

Sencore made a very handy tool for diagnosing these, and I suspect other companies did as well. It features an adapter that plugs in between the HO tube and socket, among other things. It will measure HO current and can also interject its own horiz osc frequency. I use mine quite a bit as it helps pinpoint where the problem is. If the HV will wake up with proper horiz osc. applied then you know which circuit to target. I think the B+K TV Analysts can do this as well, if you know what you are doing.