Well, interesting repair. Yes, the problem was a leaky Q1 on the
display board. Replaced with a non-descript 2N3904 since I didn't have
the 2N4124 that was bad. Schematic called for a different transistor
altogether.
Delving into the circuit also revealed why I had no PTT. Seems if the
amp detects RF output prior to PTT, then the PTT circuit is disabled. I
had no RF output, but the leaky transistor had the same effect as
rectified RF allowing voltage where it was not wanted!
Also found out the step-start circuit is fried. Read that as the power
resistor is fried. The board it's on is behind the HV transformer so I
may just leave it alone.
I know many people have Centurions. This one is a 422B, the black (and
current) faced amp. I've had it almost eight years now and it's been a
problem child. Early on in its life I lost two HV transformers.
Tentec had a problem with these and never, NEVER admitted as such. One
was replaced under warranty, the next one lasted seven months. Both
failed with shorted primaries. After the second failed, I bit the
bullet and bought a Peter Dahl and never looked back. I had Dahl
slightly up the secondary voltage on this one.
This is about the sixth repair on the unit, by far and away my least
reliable piece of equipment. Even the schematics are wrong -- and I
bought the amp after it had been on the market already for 15 years or
so. Even the board screened nomenclature was incorrect on a few boards
that I noticed while troubleshooting. I may never buy another piece of
Tentec gear again.
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