Thanks. I ordered the manual on ebay so I'll post again when I get it.


Arfa Daily wrote:
"Noam" wrote in message
ups.com...
Thanks for all the advice so far. Here is the update:
There are no shorts across the output. Also the emitter, base, and
collector of the big power transistor are not shorted to ground. But
here is something that seems wrong: there is no variable voltage on the
base of the big power transistor when the set-voltage is varied. So
there is some problem before the big power transistor. This is all I
have so far.
Any advice?

That would be the reason that there is no output. What you now need to do,
is follow the base lead back into the circuitry, and see where it comes
from. There are several ways that the adjust voltage may be produced, from a
simple pot on the base of a driver transistor with a reference from a zener
diode in the emitter circuit, to more elaborate schemes using a chip, often
a uA723 ( or any '723 equivalent ). You might try also checking that there
is some kind of varying voltage on the wiper tag of the set volts pot, when
it is rotated. This voltage may actually be quite small - of the order of a
few volts. Would it be possible for you to take a couple of photos of the
control pcb and post them up somewhere ? Might give the experienced eye a
clue as to how the regulator is designed. If you don't have anywhere to post
them, you could always send them to me direct, and I'll see if I can help
that way.

Arfa