Pete,
Almost surely, if this is a series pass power transistor circuit regulator,
And if the power regulator transistor is not shorted; it is driven by
another transistor, and that smaller transistor will have a zener to
negative bus in its base circuit. Your zener is likely open circuit, should
be one to regulate the output to 13.8 Volts accounting for two Base Emitter
drops of Silicon, which would be 1.2 volts total. Now I am not remembering
if you need 13.8 plus 1.2 or minus 1.2. You can check the number of the
defunct zener against NTE and see which voltage it is, and replace it with
same voltage and power of zener diode. The output transistor, if a series
pass regulator just has to handle the current, it does not set the voltage,
the driver transistor's base zener does that.
Those zeners should have a bypass cap to protect them; something like 0.1
MF, if not; that may account for the failure, a spike could get the zener.
Might add one if not already protected. If this is not the supply I have
described; then other Ten Tec fans, please correct. However both series and
shunt regulated circuits use a zener to set voltage in conjunction with the
voltage adjust pot.
Also, check if the TT p.s. uses a crowbar circuit across the output, and if
so, what is wrong in that it is not clamping the output and allowed it to go
to 23 volts.
73, Stuart K5KVH
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