" Uncle Peter" wrote in message
news:njy3d.282268$Lj.181967@fed1read03...

"G.Beat" wrote in message
news:FSs3d.78590$D%.30566@attbi_s51...
wrote in message
...
HELP Astron 70 amp PS
I have a astron 70 amp power supply and was hooking up a transmitter
to it and I pulled the power supply closer to me and the positive wire
came loose and hit the ground terminal on power supply.
Now when I turn it on you can hear the power supply turn on and the
light on the power swithch comes on, but no volts comes up on the
meter. I checked the terminals on the back and no volt, very little if
at all.
The outside fuse is good.
I took off top cover and I don't see and internal fuse.
Is there a diode I should be looking for?
I'm sure it has to have some kind of protection if the wires are
reversed.
Any help would be great.
Rich


Rich -

First, NEVER open a power supply case/cover while it is still plugged
into
the AC mains.

Second, ALWAYS properly discharge the electrolytic capacitors before
poking
around inside a power supply. With a power supply of this amperage - it
will have one or two very large capacitors that will still have stored
energy after being turned off.

Now. Unplug the unit, come back in a couple of minutes (allow time for
SCR
crowbar to reset) and then plug into AC mains and see if you have
voltage.
If not, then some components have likely been damaged and will require
replacing.

[snip]

The SCR DOES NOT fire on a short circuit condition. The SCR fires on
overvolage conditions, not over current. The current is sensed, and if
the current drain is exceeded, the output will fold back limiting the
current to maximum the supply is set for.

Now, the SCR might have falsely fired, and in that reguard you might
be correct in suggesting waiting several seconds with the power switch
off.

Peter


Better to check the easy items first, before disassemblying the pass
transistors (2N3055 or 2N3771) to check them and replacing the LM723 ---
which are the usual suspects.

gb