[TenTec] 9420 Problem - Update

[Christian von Wechmar]

Hi Everyone,

I'd like to thank everyone who offered advice re. my previous post. Bottom
line: The PSU is working now, but intermittently HI.

My B board was not regulating properly. I checked all the transistors, zener
etc, and everything was on spec. A good friend noticed that R3 was 5.6K, in
stead of the 1.5K indicated on the schematic. By changing it, the B board
now regulates. Strangely, it seems that the other boards have 5.6K
resistors, but are working ok. Perhaps this deviation from my schematic is
due to the fact that my boards are "Revision B". If R3 should really be
5.6K, them I'm confused.

Anyway, all works well on start-up. I've run the Herc into a dummy load
until the 9420 was quite warm, without a hiccup. But every now and then, the
"overload" lamp lights up, und stays up even when the Herc was not xmitting.
Voltage is 14V. When the PSU is cycled off/on, all is well again for a
while.

I've checked and resoldered all pads on the control board. Plugs are all
seated correctly. All boards regulate to 14V, even under load. I've run out
of ideas, and am thinking about giving up (for now at least). There's just a
little gremlin lurking somewhere. Anyone have some Gremlin-B-Gone spray?

73 Chris ZS1DX