Hello,

I've recapped this Philco 50-T702 that I've had for a few years. When i got it, it did nothing. Now, since I recapped it and I get a strange raster with a 60hz buzz. I even updated the old faulty HV circuit with a EMCO solid state unit per myvintagetv.com. I've replaced just about everything I can think of, but I may be missing something. My reference has been the SAMS Photofact and a Philco schematic book by Wallace's. I have uploaded a picture of what the screen looks like. I would appreciate any suggestions.

Thanks,
Mike
mwredit@yahoo.com

It looks like both horizontal and vertical oscillators are running far off frequency, and there could be something else seriously wrong as well.

Do you have a scope and know how to use it?

Something in the horizontal circuit is either open or a component is far off value. Have you checked all the coils?

I would not operate that TV for long with that defect.

It looks like the horizontal oscillator starts to run for a few cycles and then the amplitude starts dropping and then it stops completely. After a moment it starts again and the process repeats. I think that Jonnysan's advice is about right. An open circuit allowing the voltage on the grid to float is one possibility. Check that the horizontal hold control is not open and check the resistors in addition to the coils.

That is certainly a very strange display on your set.

Have you double-checked all of your work? It's easy to make a mistake when replacing dozens of components in a TV that you can't try out from time to time, to make sure things haven't gone sideways.

Look for:

-- Miswired cap (i.e., wrong connection)
-- Wrong value (.1 instead of .001, etc.)
-- Dropped blob of solder that makes a short circuit
-- Bent component that makes a short circuit
-- Broken connection

Speaking from painful experience (hey, anybody can make a boo-boo), a miswired component can result in a weird problem that doesn't show up on your list of classic TV symptoms.

It may help to make a fresh print of the schematic and use a highlighter to mark off every component as you confirm that it has the right value and that it's wired correctly.

Phil Nelson

Start with some troubleshooting:

1. Clean and adjust the horizontal hold and size controls
2. Replace both 12AU7s in the horizontal circuit
3. Bridge the electrolytic caps in the power supply
4. Check/replace the black molded paper caps in the oscillator circuit

Steps one and two may be enough. This assumes the trouble is a part failure and not built in.

Don

Thanks for the suggestions, I'll try all of them. Also, I've noticed that the two filter choke coils that are in the horizontal circuits look sketchy, tar covered and the size of mushrooms. Maybe those are suspect? I've replaced all the paper and "Black Beauties" caps along with the waxy ones. Well, I'll recheck the work I did and verify values, troubleshoot and go from there.

Thanks all,
Mike