Philco Tandem
 

Hi All:
I am working on a Philco Predicta Tandem and have restored the boards with the standard new resistors and capacitors. I have it all back together and have given it a try and it is somewhat working, the vertical locks in solid but right in the middle of the screen so I see the top of the picture below the middle of the screen and the bottom of the picture above the middle of the screen.
Also the HV is a little low, should be about 15KV and I measure 12kv. Any thoughts on what's going on here?
Thanks

Gregb

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I did replace two of them, K1 and K3 as both had make shift repairs done to them in the past. The horizontal is working fine and the vertical seems fine other than it locks in with the bar through the middle of the screen.

Gregb

Possible the vertical oscillator is running at twice the correct frequency. Can you check it with a scope ?

I have a little digital scope and checked it and the wave form looks good but it shows its running at 30hz not 60.

Gregb

Double check part values in the vertical stage. Replacing a part with a part that is off by a power of 10 could cause that.

Yup, I have checked and double checked. That is what I was thinking, the set did not work at all when I got it. It had a severe case of broken tube sockets so I just pulled the board and replaced all caps and most of the resistors as well as the bad sockets. Other than this problem it is working pretty good at his point. I was just ready in a vintage service book that the vertical integrator can case this very problem so I think I will build a new one and give it a try.

Gregb

Found my vertical problem, C39 is supposed to be .0039uf and is marked 332K so should be .0039uf but measures .044uf. It was one of those little reddish coloured radial lead capacitors. First time I have ever seen a new capacitor that was bad.

Gregb

If it was marked 332K, it should measure 0.0033uF. Where did you get it ?

I got them from another collector who was getting out of the hobby so not sure where they came from. I have seen very similar ones sold on ebay and a number of other sites. I usually use the yellow ones from Just Radios but had these and thought I would use them up. Worst thing is I usually check each one out of habit before installing it and I didn't this time for what ever reason.

Gregb