Rca kcs81b
 

Hi Guys:
I need a little tech support, I am working on my RCA KCS81B and cant get enough vertical even with the controls all the way to the extreme. It locks on just fine but just wont fill the screen. I checked voltages and they seem good and scoped it and everything looks good. The one thing I notice is the vert out trans makes more noise than I have noticed in other sets and the primary reads 200 ohms higher than the 620 ohms its supposed to be. Anyone think that might be the problem? Any suggestions?
Thanks

Gregb

All those RCA's needed capacitor replacement in the vertical sweep circuit. A lot of them were rather new, when needing re-capping. Either there was a non-linearity problem or the vertical hold control was on the end of it's range and still wouldn't lock. :yes:

I have completely recapped and reresistored the entire chassis. All the tubes have been tested and anything that did not test 100% was replaced with tested NOS tubes.
I double checked everything I did in the vertical section and all values match whats on the Sams info I have and when I was replacing I made sure the existing parts had the same value as the Sams showed.

Gregb

Could be bad sweep xformers...However unless the area looked like it was hacked up by a tech that had no clue what he was doing I would strongly advise you not to make the circuit look exactly like the sam's says it should. I've had sam's typos and inaccuracies screw up several restorations already (which caused lots of extra needless thinking to correct). I now ALWAYS replace parts with the same values as the original parts installed in the set unless the part markings have been obliterated, or there is evidence of old hack work that was done.

The one I learned a long time ago was never change the circuit unless hacked! In my case the chassis was very original with only two noticeable repairs and neither were in the vertical section. I do see there is a difference in the vertical circuit as compared to the Sams so I left it original just updated components.
I see that Play Things of the past has a transformer for a good price so I may give it a try as I don't know what else to try.

Gregb

I dont see the VOT going up in value. If you have access to
Sams collection find a similar chassis & see what it says
for an ohms reading. Also every VOT I remember changing
did not have otherwise "normal" vert, had small or no
sweep, bunching, pairing, retrace etc.........
Most size problems when otherwise normal are high ohm
resistors around the size control. If you dont nip off one
end to test they can fool you.

73 Zeno:smoke:

Thanks Zeno, I will check again. Most resistors have been replaced, only a couple originals remain in that area and all replacements were checked for value when installed and all originals had one end lifted when checked. What I find strange is all of the voltages check fine and all of the scoped results look good as well. I have tried a test crt and different yoke with the same results. I can get about 3/4 of the screen with the high adjustment at the end of range and at that point it sounds like the circuit is working hard to make that height, I can really hear the transformer.

Gregb

Gregb

Sams shows a Production Change Bulletin for the KCS81B chassis in Sams 265, and reflects the removal of C1C, R119, an R114. Are these present, or did you add them to jive with Sams 208?

Just a thought, as I've seen sets that I thought had been hacked as they did not agree with Sams, only to find a PCB that removed or added the parts.

I will check when I get home tonight, Thanks

Gregb

I ran home for lunch and my set is as original, I will try the production change tonight and see if there is any improvement.
Thanks

Gregb

For anyone following the thread I have made the changes as per Findm-Keepm and on my 5" test CRT I got another 1/2" of height which should translate to being good when connected to the correct CRT.

Gregb

Well I just tried the set with the 21AP4 and the vertical is better, it fills the screen and its not at the end of the adjustment so I will call it good. Looks like it needs some alignment as the picture is not very clear so will work on that next. It does sound good with its 12" speaker so may be able to assume the sound section is good.

Gregb

I was a little quick to say things are good, I adjusted the linearity and with it set properly I don't have anywhere near enough height or width. I did some reading and the book I have says the problem could to low B+ or high HV, the B+ is good but the HV is a little on the high side. The info I have says it should be 14kv and it measures 16kv. Is that enough to cause this kind of problem?

Gregb