[Kenwood] ASTRON RS-35M

[Tim Billingsley]

Tim, check the emitter resistors on the pass transistors.  If they're OK,
try disconnecting the crowbar SCR.

If disconnecting the SCR does the trick, look to the over-current
protection circuit.

73  <>  Carl

----

Check out Linear ICs application books (from Texas Instruments, National
Semiconductor or others that make LM723) and look at the pages for the
LM723 (I think) IC that is pretty much the heart of all Astron Linear Mode
regulated power supplies. Astron's design does not deviate very much from
what you will find in those books. Almost the only difference between
various models of Astron linear mode regulated power supplies is the size
ot the transformer, the size of the diodes or diode bridge, the size of the
filter capacitors and the number of 2N3055 transistors needed for the
current rating.  Ok sure that may be an overgeneralization, but it is not
very far from the truth.

DE N6KB


----
OK. Here's the deal. This MAY NOT be related to your problem, but you may
wish to check
it anyway.

According to Astron, there are two components associated with the LM-723
which may be
causing trouble: these are C-3, which is connected to pin 15 of the LM-723.
It is 0.01 mfd at
50 volts. Remove this cap in every case.

Secondly, already silkscreened onto the board is R-3X, but it may or may
not be installed.

If it is not installed or if it is the incorrect value, it should be 5K
ohms at 1/2 watt.

Install that.

What happens when R-3X is missing is that at the upper limit of current
capability, there is
too much hysterisis in the system and it shuts down. This MAY be related to
your issue.

On one end, R-3X connects to pin 2 of the LM-723 and goes to common on the
other.

Lastly, there was a problem common to all of the Astron power supplies I
worked on (this
was back in December of 2005, BTW) in that the output connectors may be
missing their
flat-washers, and maybe even their lock washers. In attempting to tighten
the output
connectors, one can instead loosen the entire bolt associated with that
connector. This
causes a large voltage drop at the output connector which then causes the
supply to lose
control.

I had to replace the LM-723 in at least one of the supplies I worked on as
the original one
would not regulate properly.

I used an LM-723CN, a military grade unit, which has much "tighter"
specifications than
some of Astron's originals.

One of the 35A power supplies I repaired then showed 13.72 volts at no
load, and 13.80
volts at a load of 35 amps.

Anyway, let me know if this helps or not.

Ken W7EKB

----

Aw heck,
Tie up the list so the rest of us will have some good reading. That's what
the list is for; not to grow flowers and be quiet. That's how I find things
out. It's wonderful that others with so much knowledge are willing to help
out and it is also wonderful that even though I don't have the problem I
get a lot of information I may need later.
Best regards,
Ralph Howes
w8bvh


----

On 11 Nov 2016 at 23:34, Larry L. Hinton wrote:

>
> Sorry for the intrusion Ken,
>
> This information is good to know as I have three of Astron's power
supplies. None have gone
> bad yet, but there is no reason not to make improvements.
>
> One item to be careful with. All the data sheets I have show the LM-723C
as Commercial Temp
> (0C to 70C). The LM-723 is the Industrial/Military Temp (-55C to 125C).
One in particular is from
> STMicroelectronics.

Thanks, Larry.

When I did the work, it was in 2003, and the version I chose was the CN,
not the C version.
I don't know how things have changed since then, but I would certainly
choose the more
highly rated unit now.

vy 73 for now,

Ken W7EKB

----



Thank you all for your assistance and instruction. This will take me a bit
to work through given my abilities and the fact that y'all say this stuff
like I am an old hand at thisf. Unfortunately I am re-learning as I go.
Some f the stuff y'all have directed me to do I simply have no concept
where to start. I hate to come off as a big dummy but it is what it is. I
will start taking pictures as needed, but I have no idea what EXACTLY I am
supposed to be looking for in some of these instances and I hate to just
guess.  I would (when all of this is over and done and the PSU is working
properly again) like to put together a presentation for our club on how to
diagnose and repair PSU issues, but first I have to learn what I am doing.
Y'all's patience and instruction is appreciated. Take this to a remedial
level and offer diagrams or pictures so I know better what I am looking for
and not just tearing stuff apart in a hit and miss kind of tangle. Act like
I have never done this kind of stuff before and you are having to point to
each part and say "That is what you are looking for right there" and keep
in mind I am fighting chemo fog, shakey hands, bad eyes, and the attention
span of a gnat, but I am trying.

http://www.repeater-builder.com/astron/pdf/rs35m-2009-k2qde.pdf
http://www.repeater-builder.com/astron/astron-repair/astron-repair.html
http://www.repeater-builder.com/astron/pdf/power-supply-analysis.pdf
http://www.repeater-builder.com/astron/astron-index.html