Dammit !, anywat, NAP 31X3 chassis

" snipped-for-privacy@aol.com" bravely wrote to "All" (03 Aug 05 22:31:11) --- on the heady topic of "Dammit !, anywat, NAP 31X3 chassis"

A Ne2 bulb or a Zener diode at the CRT pin to ground, your pick? Could be the glitch is indirectly injected through a large junction into the IC's supply lines. In which case paralleling a 0.1uF bypass disc cap across the IC's supply might catch it better than the electro sitting there. Sneaky little problem there...

A*s*i*m*o*v

ZZ> From: snipped-for-privacy@aol.com ZZ> Xref: aeinews sci.electronics.repair:54920

ZZ> Sorry, the last post was a test. Friggin Google will sit there and let ZZ> me type for an hour and THEN ask for login, which loses it all.

ZZ> Anyway, I'd like to know the mechanism by which the CRT blows the ZZ> chroma, or more aptly the -Y outputs of IC200. I can't see how this ZZ> cannot be protected against, and I'm still having trouble even ZZ> believing this is the cause.

ZZ> I have had wierd stuff in the past, V height for greyscale, open ZZ> speaker causing no HV, I am not a babe in the woods. What I'm having a ZZ> hard time understanding is how any phenomenon connected with the CRT ZZ> could do this again and again without blowing any other components in ZZ> the path.

ZZ> I have solved a similar problem in a CTC169, I just found a transistor ZZ> that was fairly linear in gain, but had a 400 volt Vce to replace that ZZ> ECG123 (or was it a 159 ?) equvalent. It never blew the chip, but ZZ> maybe RCA's chip of the day had better protection. What's more IIRC ZZ> that transistor is the last stop in the Y driver chain.

ZZ> Is possibly the collector to base capacitance saving these transistors ZZ> by delivering the jolt to the chip ?

ZZ> Seems to me a way could be figured out to protect it from that, that ZZ> is if I knew the failure mode. I have never witnessed it and as yall ZZ> know, even if I had I might still know nothing. I might know something ZZ> but I might not. I would have seen it, but I have not.

ZZ> Ideas ?

ZZ> JURB

ZZ> TIA

... Which sparks some mnemonic circuitry.

Could be the glitch is indirectly injected through a large junction into the IC's supply lines. In which case paralleling a 0.1uF bypass disc cap across the IC's supply might catch it better than the electro sitting there. Sneaky little problem there...