CTC-11 Help, Cap question
 

HV is only about 5KV and plate voltage on 6DQ5 starts at around 330V, drops to 48, then gradually increases and tops out at 118 give or take when the chassis is powered up. The wirewound resistor in series measures 12.75K and it gets extremely hot compared to the others in the set so I'm wondering if it's gone off value and keeping the voltage way down there. (Don't have a schematic yet so this may not even be close.)Input voltage from the HO board is -46V.

The electrolytics test good, but... Again, powering up the set, some of the higher voltage sections top out at around 400-440V and gradually drop to 278 - 330, depending on the section being tested. I know in some applications, a voltage drop of 5-10% is nominal but this seems a little extreme.

I'm using a Fluke 12 to test the caps but know. too, that what tests good may not function satisfactorily under load. Outside of buying an ESR tester, what's your 'foolproof' method of testing electrolytics? In the past, I've just replaced 'em all but this gets a little expensive at 8-12 or more per set. Just keep replacing them and live with it?

Thanks for any help you can give!
Michael

CTC-11
 

Michael,

The voltage at the grid of the 6DQ5 should be -57 volts. The voltage on the screen shud be +145 V. You should have +390 volts on the plate of the 6AU4 damper. In the first electrolytic cap of the power supply C125 (160 uF) positive lead to ground shud be +405 volts.

On the terminals on the PW600 horizontal oscillator board Pin A shud be +386 volts, and H +275 volts. Pin 6 (output plate) of the 6CG7 oscillator shud be +260. The other plate pin 1 shud be +24 V.

There is an R108 which is a 10K on the boost B+ line, one side goes to the blue wire on the deflection yoke.

I could scan the schematic and email to you if you want. Email me (not PM) your real email address which can handle large attachments.

Rob

CTC-11 Cap Prob
 

Thanks to Rob, I got my HV back! Replaced both 160uf's & voltages checked in spec. or nearly so. I now have color but pretty smeary w/hum bars (I guess)--top/bottom of pix goes nearly black on some scenes w/white or lighter horiz. bars across screen when titles or light components of some scenes are being displayed. I'm guessing a coupling cap or something causing a heater to cathode short? Anyway, thanks Rob!

Michael, you probably still have weak or leaky electrolytics elsewhere. As far as the picture problems you just described, try re-adjusting the AGC control on the rear of the chassis and see if that helps. Too much gain can make symptoms like that.

I didn't get a chance to scan the schematic today but I will soon.

Rob