"Noam" wrote in message
oups.com...
Hi,

I have an old 0-100V (0.2A) HP power supply (HP 6116A), which is
broken. The output is always 0.6V (when on). Nothing is obviously
burned or exploded inside.

The problem started when one of the people in my lab connected a
capacitor backwards across the supply's output, giving it a large
negative voltage spike.

Any ideas on what could be the problem? The supply has a transformer
and several largeish capacitors. However, the inner circuit is pretty
complicated. My guess is something near the output is broken, but what
could it be?

Any advice would be greatly appreciated.


Best guess would have to be the series pass transistor ( probably fairly
large and on a heatsink ).

Confirm with a voltmeter that there is a highish voltage on its input -
probably 120v or so and may be on the collector or emitter depending on
whether it's an NPN or a PNP type. If input volts are present, check for a
voltage on the base connection, which varies up to around 100v with rotation
of the set voltage pot.

If there is no input voltage, problem is back in the raw stage ie rectifier
/ smoothing / maybe surge limiter resistor.

If the variable voltage is missing, disconnect, base lead and check again.
If it's still missing, problem is back in control loop. If adjustable
voltage is present, and input voltage is present, check to make sure that
there are no shorts across the output of the transistor ( decoupling cap,
protection diode, overvolt zener ) then replace transistor.

Obviously, this is a fairly simplistic approach, and assumes that it is a '
conventional ' design linear supply, but should catch most common problems
for this type of fault. If problem does prove to be in the control loop,
then things will get rather more complicated, but suspicion should fall
first on any semiconductor devices ( transistors, control chip, diodes,
zeners ).

Arfa