Astron Power Supply Repair
Bob Wilson
I have an Astron RS-35M with a shorted output transisitor. It uses 4 2N3771's
made by Motorola in parallel. My question is: does Astron match output
transistors or will any Motorola 2N3771 balance out OK with the other 3 output
transistors? Thanks
Bob
Chris Jardine
As I recall from the days when I repaired many Astron RS-XXX Power
supplies, they all use the 2N3771 output transistor. I also seem to
remember an Emitter balancing (.1 ohm or less) resistor that took care
of the balance issue. I therefore think you are safe in simply using
any 2N3771 in this case. It seems to me that I did just that quite a
number of times.
I hope this helps!
Chris Jardine
CJ Electronics
cjar...@wctc.net
Joseph E. Fealkovich
In <5lcdhg$p...@mic14.redstone.army.mil> rwi...@hiwaay.net (Bob Wilson)
writes:
>I have an Astron RS-35M with a shorted output transisitor. It uses 4
2N3771's
>made by Motorola in parallel. My question is: does Astron match
output
>transistors or will any Motorola 2N3771 balance out OK with the other
3 output
>transistors? Thanks
>Bob
>
Hi Bob, I remember the Astron power supplies, very good power supplies.
On your question, you should be able to use any Motorola devices for
the shorted 2N3771. Reason being is if memory serves me right, each
pass transistor has a fairly large low value resistor coming off it's
emitter lead. That helps all four pass transistors share the load, so
no one transistor is working harder than any other one. Hope this helps
and good luck!:)
Joe at jef...@ix.netcom.com
Bob Wilson
OK I will try a Motorola transisitor. The reason for my concern was I
notice
that the emitter resistors were only .05 ohms. I thought this was a pretty
small value and would require additional transistor matching.
Bob
Laurence Taylor
In article <5lcdhg$p...@mic14.redstone.army.mil>
rwi...@hiwaay.net "Bob Wilson" writes:
-> I have an Astron RS-35M with a shorted output transisitor. It uses 4 2N3771's
-> made by Motorola in parallel. My question is: does Astron match output
-> transistors or will any Motorola 2N3771 balance out OK with the other 3 output
-> transistors? Thanks
-> Bob
I don't think anybody matches transistors any more. Usually devices from
the same batch will be close enough. However, I wouldn't advise
replacing just one in your set; if they are in parellel, replace them
all.
rgds
LAurence
Douglas M. Keith
With video you can see it onscreen,audio you must hear it?
*4th
Pom E Granate
Bob Wilson <rwi...@hiwaay.net> wrote in article
<5lcdhg$p...@mic14.redstone.army.mil>...
> I have an Astron RS-35M with a shorted output transisitor. It uses 4
2N3771's
> made by Motorola in parallel. My question is: does Astron match output
> transistors or will any Motorola 2N3771 balance out OK with the other 3
output
> transistors? Thanks
> Bob
Several other comments were made concerning the low-ohm resistors
around the pass transistors, and the use of Motorola replacements.
I concur with these, and would also recommend a thorough lookover
of the regulator board mounted atop the large filter cap. I had an RS-35A
from a ham come into the shop 6 months ago, and found no less than
four (4) cold or poor solder joints on the board, and there was corrosion
around the PCB "rings" which made contact with the large cap to which the
board was mounted. Unit came in with the complaint of "surges"
(intermittent
bursts of audible 60 cycle hum under load) When I re-soldered the cold
joints and cleaned the capacitor contact pads with some non-residual
cleaner in a lint-free cloth, the surges dissappeared and unit worked
100% under varying loads. Lessons learned: Check all Astron's for poor
workmanship/solder connections. (The one I worked on was assembled
in Mexico...)
Frank Scaraglino
control allowing the pass transistors to blow
Frank
Mark Shepherd
Pom E Granate (seno...@earthlink.net) wrote:
:
: I concur with these, and would also recommend a thorough lookover
: of the regulator board mounted atop the large filter cap.
I concur. This is the first Astron I've ever worked on, but I am
fixing an RS-35A for the local emergency management folks.
On first opening the case there were two lead wires and a rubber plug
that used to be a 2200 uf electrolytic capacitor across the output
bolts. The rest of it was kind of spread all over that corner of
the supply. Also one lead wire to the MOV soldered to the 120V input
just below this cap had broken.
I fixed those things, but something told me, 'look around before you
fire it up'. Checking the 3771's revealed that out of 4 alleged
transistors, I had 2 transistors, one kinda funky diode, and one really
neat piece of wire in a TO3 can. So those will be replaced. Also,
I found a couple of burnt .25 or .5 watt resistors on the control
board mentioned above; had to send for the schematic to figure those out.
(OK, OK, I probably should have worked it out myself, but I am
still at a 'intermediate hacker' level of fixing things... :) )
Don't remember which resistors were burnt, offhand, but if there is
burning interest I can post about them later. Right now I am awaiting
3771's and checking to see what else is broken.
Some trivia on these supplies....
They use a 723 regulator IC on the above mentioned board
AFAIK, 'A' models have no output meters, and 'M' models do
The 35 amp model is really rated 24 amps continuous; 35A on a 50%
duty cycle
2N3771 = NTE181
Hopefully this is not too much of a rehash for everyone.
Matt Roberds
mrob...@cyberramp.net
(or elv...@galstar.com; I've just moved and email is funky
for the moment)
73k...@gmail.com
Fred McKenzie
have had a couple of the regulator IC's go bad, but never a pass
transistor. I would first suspect a short external to the transistor!
The original 2N3771 transistors may come out of the same batch, but
probably are not matched. Each one has an emitter resistor to help
equalize current. Therefore you should not have a problem with un-equal
current due to replacement transistors.
The current meter measures voltage drop across one of the 4 emitter
resistors. It may need slight re-calibration, but you should have no
trouble with a replacement 2N3771.
Fred
Michael Black
> In article <ac61acb6-9240-49c1...@googlegroups.com>,
> 73k...@gmail.com wrote:
>
>> On Wednesday, May 14, 1997 at 2:00:00 AM UTC-5, Bob Wilson wrote:
>>> I have an Astron RS-35M with a shorted output transisitor. It uses 4
>>> 2N3771's
>>> made by Motorola in parallel. My question is: does Astron match output
>>> transistors or will any Motorola 2N3771 balance out OK with the other 3
>>> output
>>> transistors? Thanks
>>> Bob
>
> This is a little old, but Astron power supplies are still around. I
> have had a couple of the regulator IC's go bad, but never a pass
> transistor. I would first suspect a short external to the transistor!
>
The guy who restarted this thread didn't even bother to say anything, just
took a 20 year old post and reposted it.
There was no question or comment.
Michael
Fred McKenzie
Surely someone is interested in the discussion. As I mentioned, there
are a lot of the Astron analog power supplies around. The design has
only slightly evolved since the 1980's, and they are still being
produced.
Fred