#1
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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 |
#2
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HV ok?
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#3
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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. |
#4
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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 Last edited by old_coot88; 07-22-2011 at 10:10 AM. |
#5
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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. |
Audiokarma |
#6
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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 |
#7
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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. |
#8
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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
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Collecting & restoring TVs in Los Angeles since age 10 Last edited by kx250rider; 07-31-2011 at 11:45 AM. |
#9
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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.
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#10
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BTW. when you change those caps you MUST check the cathode current and adjust the effency coil.
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Audiokarma |
#11
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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?
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#12
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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. |
#13
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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 |
#14
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While looking for Caps , see if the HO screen volts is being pulled down. Those leaking buggers can cause trouble anywhere.
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#15
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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. |
Audiokarma |
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