Capehart 325 restoration

[bandersen]

I could use his help right about now

Replacing the drive control has stopped the fuse from popping. It appears to be tin plated but I couldn't really see any whiskers.


All the resistors and capacitors on the HOT have been replaced and DC voltages seem reasonable. The cathode waveform matches whats shown in the service info.


I've also tried swapping out each of the the three tubes inside the HV cage, but the low HV issue remains. Only about 6.5 kV under load. Just for the heck of it I installed a full size CRT, and you can see how dim and unfocused it is.


So it seems to me that leaves the two high voltage ceramic caps inside the cage, the yoke and the flyback as culprits

[Doug66]

While looking on ebay, I noticed a similar one located one state up from me. Viewing the listing showed it had been robbed of some parts: tubes and looks like 12" speaker. What actually concerned me was the power transformer laying in the bottom of the cabinet with frayed wires while a power transformer was still mounted in the chassis. All that, the $100 opening bid, and the condition of the cabinet was enough to turn me off of it.


http://www.ebay.com/itm/Original-195...item3395211702

[robert1]

Originally Posted by bandersen

All the resistors and capacitors on the HOT have been replaced and DC voltages seem reasonable. The cathode waveform matches whats shown in the service info.

how about the voltage on the cathode of the damper tube? it should be around 550 V. if not, the low end of the winding on the flyback most likely has shorted turns.

Originally Posted by bandersen

I've also tried swapping out each of the the three tubes inside the HV cage, but the low HV issue remains. Only about 6.5 kV under load. Just for the heck of it I installed a full size CRT, and you can see how dim and unfocused it is.
So it seems to me that leaves the two high voltage ceramic caps inside the cage, the yoke and the flyback as culprits

i would say that the flyback has a few shorted turns. have you done a "ring" test on the flyback transformer yet?. that can be more revealing than a ohmeter can be.

[bandersen]

Originally Posted by robert1

how about the voltage on the cathode of the damper tube? it should be around 550 V. if not, the low end of the winding on the flyback most likely has shorted turns.

I have 355 VDC. Capehart service info just says HV for that voltage. Sams says 250 VDC.

Originally Posted by robert1

i would say that the flyback has a few shorted turns. have you done a "ring" test on the flyback transformer yet?. that can be more revealing than a ohmeter can be.

Yes and it passes.

[robert1]

Originally Posted by bandersen

I have 355 VDC. Capehart service info just says HV for that voltage. Sams says 250 VDC.
Yes and it passes.

Sams Says 550 v on the cathode of the 6W4 & 280 v on the plate of the 6W4. When measuring the cathode, is that where you got the 355 volt reading? the voltage on the plate of the 6W4 is supposed to be 280 v & is 20 volts low.
if the cathode of the 6W4 is reading 355, it is too low & is a possible indication that something in that immediate circuit is drawing too much current. after all, that is the B-Boost circuit. that also could be the cause of the low B+ voltage (250v)