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Author Topic: SOS...Astron RS-35m sudden voltage loss...SOS  (Read 5647 times)
N0OG
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Posts: 13




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« on: June 01, 2010, 08:01:12 PM »

I'm in the middle of building a Bitx20 V3 xcvr (my only radio) and I was checking voltages on some of the transistors and I was getting weird readings. I fiddled with the circuits for a while until I looked up at the power supply and saw that it was only putting out about 1.5V. I unplugged it and took the cover off and everything looked normal--no loose wires. I did have problems with the switch yesterday--where when I switched it off, it stayed powered on. I fiddled with the switch--popped it in and out of its housing--and it worked fine. Thoughts?Huh
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KE3WD
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« Reply #1 on: June 02, 2010, 08:11:57 PM »

That power switch *might* be arcing inside, not an uncommon problem. 

To find out, safely bypass the switch and see if the PS works okay that way.  You can use a plug strip as the off-on switch while you do that. 

If that proves to be the case, then you should order a new switch. 

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AB4D
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« Reply #2 on: June 08, 2010, 05:54:35 AM »

The problem could be the IC on the regulator board, this is a common failure on the astron supplies.  They are easily replaced for a few dollars, I believe it is the common LM723, get a socket too if the IC is not socketed, makes replacement a snap.
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AA4PB
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« Reply #3 on: June 08, 2010, 06:45:36 AM »

Just as a side note, I don't like using a big 35A power supply for testing relativly low current devices like a QRP rig or receiver. The reason is that any short in the circuit you are building can wipe out circuit board runs with 35A. If you don't have a smaller current limited supply available, at least put a 1 or 2A fast blow fuse in line on the output of the power supply.
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KB3HG
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Posts: 404




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« Reply #4 on: July 21, 2010, 12:46:19 AM »

N0OG,
Get it fixed yet?

Tom Kb3hg
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KB3HG
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Posts: 404




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« Reply #5 on: July 21, 2010, 12:47:39 AM »

Do You Have a Schematic?

Tom Kb3hg
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N2JXN
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Posts: 189




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« Reply #6 on: July 23, 2010, 05:39:49 PM »

http://www.repeater-builder.com/astron/pix/astron-rs35m-2000-01.jpg

Here you go
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WM9V
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Posts: 106




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« Reply #7 on: July 25, 2010, 09:21:37 AM »

ya this switch is available at most appliance supply warehouses and on the internet and yes they go bad
another thing we have noticed over the years is that the electrolyte on the pcb dries out
the large one the pcb
also the 723s go bad
another big problem is arcing and bad connections where the screws go in to the large filter cap
on the pcb
get the schematic off the internet and follow it religiously
it has volt readings.... use them and when you ask questions or post,  put them in your post



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KB5PQL
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« Reply #8 on: October 02, 2010, 09:31:49 PM »

The problem could be the IC on the regulator board, this is a common failure on the astron supplies.  They are easily replaced for a few dollars, I believe it is the common LM723, get a socket too if the IC is not socketed, makes replacement a snap.

The same thing happened to me. I just pushed the IC back in the socket and that was it! fixed!
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KJ6EAD
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Posts: 56




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« Reply #9 on: October 02, 2010, 10:24:24 PM »

Wear your safety glasses! The way you're headed with your fiddling, you may need them.
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W0BTU
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« Reply #10 on: October 05, 2010, 09:05:25 PM »

I see a lot of posts concerning problems with this power supply!

This is kind of concerning to me, because I have one.

How to prevent failures? MOV's?
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AD6KA
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Posts: 2238




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« Reply #11 on: October 05, 2010, 10:12:09 PM »

Just as a side note, I don't like using a big 35A power supply for testing relativly low current devices like a QRP rig or receiver. The reason is that any short in the circuit you are building can wipe out circuit board runs with 35A. If you don't have a smaller current limited supply available, at least put a 1 or 2A fast blow fuse in line on the output of the power supply.

Well said Bob, this advice should be included in all QRP
kit instructions
. I build a LOT of QRP kits but use my
SEC 1223 because it's small enough to keep on the desk and
not get in the way. The bigger PS's are on the floor behind
the desk, I don't need the 1223's 23 Amps for QRP work, so my
QRP DC line includes a blade fuse holder.
I keep a 1 or 2A fuse in there at all times.
The blade fuses are quick and easy to change out too,
if you want more crrent for another project.

Thans agn for posting this. 73, Ken AD6KA
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K1DA
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Posts: 525




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« Reply #12 on: October 06, 2010, 11:31:04 AM »

   There is a lot of energy contained in the filter caps on an Astron 35
and they will still be charged by the transformer/bridge even if the output is low..(unless you have had a bridge or transformer failure which is unlikely but not unheard of) so be careful with the  test probes.  My experience with 35's is that they will clamp the output if the output connections  are shorted and appear to be "dead" until the short is removed.    You need proper unregulated voltage from the  bridge/filter cap, proper output from the 723 to the driver transistor and proper output from the driver to the bases of the regulators for the thing to work properly.  Buy a couple of 732's they are the usual culprit, as the others have pointed out.  Never hurts to have a spare. 
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