RCA portable insuffient B+ Boost
 

Hello all!

I am new and I was wondering if you could help me. I am working on a RCA portable EJ507J CTC22 and the B+ Boost is about 480 volts it should be 720 volts. I get a picture but the horizontal is half the size. Like I have a short in the horizontal winding of the yoke. I used a ringer on the flyback and the yoke and they both check out fine. When I first turned on the set after I recieved it and I found a puddle of wax in the flyback cage after I ran it for 20 minutes. I can supply more information if needed. If you can stear me in the right direction to solve this problem I would be gratefull. Also could someone explain the 2 damper diode in parallel.


Thanks

HV ok?

Just a guess here, but if the horz is narrow, perhaps all the Horz is weak (not just the boost) so I would start with a new HORZ tube. check the B+ and the HOT current as well. check the voltages on the screen of the HOT.

wax drippings from the fly are to be expected.

The failure rate of the SS damper diode was so high that there was a replacement consisting of two diodes strapped in parallel, intended to improve reliability. It was non-RCA sourced, IIRC.
Is that dual diode running sizzling hot by any chance?
oc

Check the Boost filter cap. If it goes open it will cause this exact issue. Its a small value cap between the boost and B+.

Ring testing a flyback will only catch hard core shorts in the primary. I have 2 flys here that ring out at 22 rings which is excellent but provide plenty of smoke when in the set.

Keep a close eye on that flyback temp, if there is an issue causing excessive heat and current you can damage an almost impossible to find part.

Thanks all for the replies. I have not replaced any of the tubes yet. I will start with the horizontal output and the hv regulator. I also checked any the capacitors between the B+ and boost found then good. The damper diodes are also good. I will replace the tubes and get back to you all.

Thanks

I tried a new HOT and regulator tube and it did not fixed the problem. I am having trouble understanding where the boost is created on this set. Where would boost filter cap be located? There are several caps on the horizontal output board that I think would create boost but I can't pin down the one that creates it. By the way this is my first tube type tv repair. Further assistance would be appreciated.

Thanks.

I think you have a B+ problem... Check the raw B+ voltages at the filter caps. Also, if there is a shorted turn in the FBT windings, it can pull down the whole line without screwing up the horizontal oscillator, and sometimes be missed by a ringer test... so hopefully that's not it in this case...

Charles

Check the b+ at point 2 like kx250 says. If you dont have an eye type cap tester replace all the caps circled. Could be the fly but usually they smoke.


http://justsmog.com/Clay/CTC22.gif

BTW. when you change those caps you MUST check the cathode current and adjust the effency coil.

out of curiosity, is your HO tube running hotter then normal after a few miniutes of the set being turned on? OR, is the HO tube showing any signs of redplating or a red spot on the plate?

The plate on HO tube does not glow red. I just ordered some orange drops for the HO board so I will wait and try it when I install the new caps. I hate admit as being new to tube tv repair I tried to check the cathode current on the HO tube and I destroyed the reset button. I did not use the .47uf cap in the instructions because I did not have one. I ordered one along with the other caps. The instructions are vague to me, what is the proper way to do it.

Thanks.

When you open the HV cage, what's it smell like in there? Any hint of a scorched odor? Or does it smell nice and 'fresh'? Old techies generally developed a "nose" for servicing which often presented the first clue to the failed component.
oc

While looking for Caps , see if the HO screen volts is being pulled down. Those leaking buggers can cause trouble anywhere.

I replaced the caps circled in the schematic and I checked the HO cathode current. It is 300ma. The horizontal efficiency coil has no affect. Bad flyback?

Thank you for your support.