[Kenwood] TS-850S DC-DC Converter Board

[Dr. Gerald N. Johnson, electrical engineer]

I'm curious how a failure on this board could produce the varying ALC
reference without killing it completely. Its as if the gain of a
transistor has gone marginal and the oscillation of the board varies
greatly with a slight change in supply voltage. But the circuit should
be so far from such marginal operation I don't readily see how that
should happen.

Maybe the 12 volt switching kills the reverse junction base-emitter and
does make the oscillator super sensitive to supply voltage. It could be
necessary to find full spec sheets on the original transistors. Maybe
Kenwood used a slightly delicate transistor because it was handy, not
selecting its VBE capability for the -12 volt transient when the
opposite transistor turns on. Maybe watching various points of the
circuit with a wideband scope will show something wandering.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.