Dear NewsReaders, I have a Astron RS-20A power supply that has started
blowing its fuse even without a load. Until now it has been perfectly
reliable. I would be much obliged for any advice as to what to look
for first as I try to repair it.
Sincerely, Carl KB2KDV

Carl Franck wrote:
Dear NewsReaders, I have a Astron RS-20A power supply that has started
blowing its fuse even without a load. Until now it has been perfectly
reliable. I would be much obliged for any advice as to what to look
for first as I try to repair it.
Sincerely, Carl KB2KDV

Possibly a bad pass transistor. Try pulling each pass transistor out
one at a time (or pull them all out and put them back one at a time
until you blow a fuse) or if you have a transistor checker, check them.
Another possibility, is you are getting an over voltage and the
crow-bar circuit is activated. This could be caused by a problem in the
regulator circuit. Possibly a bad LM723 regulator IC. These chips are
pretty inexpensive and readily available.

Andy
WD4KDN




--
Gun Control works!!! 3 million Holocaust victims can’t be wrong.

Carl Franck wrote:
Dear NewsReaders, I have a Astron RS-20A power supply that has started
blowing its fuse even without a load. Until now it has been perfectly
reliable. I would be much obliged for any advice as to what to look
for first as I try to repair it.
Sincerely, Carl KB2KDV

Possibly a bad pass transistor. Try pulling each pass transistor out
one at a time (or pull them all out and put them back one at a time
until you blow a fuse) or if you have a transistor checker, check them.
Another possibility, is you are getting an over voltage and the
crow-bar circuit is activated. This could be caused by a problem in the
regulator circuit. Possibly a bad LM723 regulator IC. These chips are
pretty inexpensive and readily available.

Andy
WD4KDN




--
Gun Control works!!! 3 million Holocaust victims can’t be wrong.

Carl Franck wrote:

Thanks for the fast help Andy!, Carl

: Dear NewsReaders, I have a Astron RS-20A power supply that has started
: blowing its fuse even without a load. Until now it has been perfectly
: reliable. I would be much obliged for any advice as to what to look
: for first as I try to repair it.
: Sincerely, Carl KB2KDV

Carl Franck wrote:

Thanks for the fast help Andy!, Carl

: Dear NewsReaders, I have a Astron RS-20A power supply that has started
: blowing its fuse even without a load. Until now it has been perfectly
: reliable. I would be much obliged for any advice as to what to look
: for first as I try to repair it.
: Sincerely, Carl KB2KDV

I would first check the diodes between the transformer and filter cap.

To prevent causing more problems do service checking with a 100 watt light bulb
in series with the AC line. This bulb normaly should glow bright for a second
when power is applied (Chargine filter caps.) then fade to dim if all is ok.
(no load)
If it continues to be bright with no load on supply you still have problem.
This limits current thru transformer. Saves fuses and transformers or circuit
boards.

good luck,
Don

I would first check the diodes between the transformer and filter cap.

To prevent causing more problems do service checking with a 100 watt light bulb
in series with the AC line. This bulb normaly should glow bright for a second
when power is applied (Chargine filter caps.) then fade to dim if all is ok.
(no load)
If it continues to be bright with no load on supply you still have problem.
This limits current thru transformer. Saves fuses and transformers or circuit
boards.

good luck,
Don

N0DG wrote:

Thanks for those ideas Don. It's hard to believe that I threw away
several fuses yesterday, I'm sure your last suggestion will save me
real $. 73 de Carl KB2KDV



: I would first check the diodes between the transformer and filter cap.
:
: To prevent causing more problems do service checking with a 100 watt light bulb
: in series with the AC line. This bulb normaly should glow bright for a second
: when power is applied (Chargine filter caps.) then fade to dim if all is ok.
: (no load)
: If it continues to be bright with no load on supply you still have problem.
: This limits current thru transformer. Saves fuses and transformers or circuit
: boards.
:
: good luck,
: Don

N0DG wrote:

Thanks for those ideas Don. It's hard to believe that I threw away
several fuses yesterday, I'm sure your last suggestion will save me
real $. 73 de Carl KB2KDV



: I would first check the diodes between the transformer and filter cap.
:
: To prevent causing more problems do service checking with a 100 watt light bulb
: in series with the AC line. This bulb normaly should glow bright for a second
: when power is applied (Chargine filter caps.) then fade to dim if all is ok.
: (no load)
: If it continues to be bright with no load on supply you still have problem.
: This limits current thru transformer. Saves fuses and transformers or circuit
: boards.
:
: good luck,
: Don

Also check the bridge rectifier or the 4 diodes, don't recall what was in
there.
Maybe one or all are shorted?

Nitespark wrote:

Carl Franck wrote:
Dear NewsReaders, I have a Astron RS-20A power supply that has started
blowing its fuse even without a load. Until now it has been perfectly
reliable. I would be much obliged for any advice as to what to look
for first as I try to repair it.
Sincerely, Carl KB2KDV

Possibly a bad pass transistor. Try pulling each pass transistor out
one at a time (or pull them all out and put them back one at a time
until you blow a fuse) or if you have a transistor checker, check them.
Another possibility, is you are getting an over voltage and the
crow-bar circuit is activated. This could be caused by a problem in the
regulator circuit. Possibly a bad LM723 regulator IC. These chips are
pretty inexpensive and readily available.

Andy
WD4KDN

--
Gun Control works!!! 3 million Holocaust victims can’t be wrong.