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Astron RS-35M Radio Shuts Down

Happy_Hamer

Administrator
Staff member
Mar 22, 2001
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I need a few ideas as where to start looking to repair my Astron RS-35M

I hook it up to a TS-2000, FT-897D, V8000, TM-D710A and the instant I key up, it shuts the radio down.

I bought it from someone cheap because they had this problem.

I tried hooking it to different antennas and even a dummy load thinking it was RF but no matter what, it still shuts down.

I looked at the repeater builder site and it is informative but overwhelming for me (I'm a simpleton LOL) , I just have a volt ohm meter and don't know where to start.

Any ideas from someone who may have had the same issue?
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,732
10,715
823
58
Nova Scotia,Canada
You can get the schematic here. just scroll down after it opens to see the RSM-35 model.


http://bama.edebris.com/manuals/astron/all


It sounds like the regulator is not holding. If you have another LM723 swap it out. If you don't have one get one. :love: Measure the voltage output without load and again when it shuts down under load. I suspect you will see a few tenths of a volt. Check that R5 has not been cranked wide open to get more voltage from the supply. It may be causing the protection circuit to trip when current is drawn. Start there and see what happens.
 
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hookedon6

W9WDX Amateur Radio Club Member
Jun 21, 2008
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be aware that even tho you have the schematic for an RS35M,.... they are not all alike,...
one astron may be slightly different that another of the same model
 
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Crash Ash

W9WDX Amateur Radio Club Member
Sep 24, 2011
71
18
18
El Segundo, CA
This may sound strange but move the power supply as far away from the radio and also don't let the coax lines come close to the power supply lines. I have a Yeasu FT897D and when I added a MFJ 4275MV power supply to the shack to power a Kenwood TM-V71A, the 897 would reset on HF. Moved the equipment around and problem solved.

Hope this helps.
 

TonyV225

W9WDX Amateur Radio Club Member
Apr 18, 2005
5,824
314
143
Wisconsin
I am with C.K. on a regulator failing under a load. Bill, did you test or check the voltage as its sitting at idle?? I would check that with the VOM and leave the probes or leads connected and see what happens with the voltage and if it drops off when you key the radio and a load is applied.
 
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137

Member
Jun 6, 2011
54
1
18
Middle TN
I have the same supply, I had to replace the pass transistors in the back, I sold it a while back but I'm pretty sure the numbers cross referenced to the common 3055 TO-3 cased transistors that radio shack carries, they just pull right out once you take the 2 screws that hold them out, once they're out make sure you squeeze the pin connectors together a little, just so they make good contact. but mine was doing the same thing as yours, hope it helps.
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,732
10,715
823
58
Nova Scotia,Canada
I would think that failed pass transistors should cause the crow bar circuit to trip as soon as the supply is turned on either with or without a load. It seems HH's problem only appears under load.
 

137

Member
Jun 6, 2011
54
1
18
Middle TN
I don't disagree at all, but after changing out most available components, mine ended up being the pass transistors... You're right it would shut down, if they were shorted, mine must have been open? Either way, replacing them was easy, so, just passing on since I had the same supply.
 
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buickid

Active Member
Nov 22, 2012
208
99
38
Kona, Hawaii
I bought a broken RS-35A for $20 IIRC, only put out a few volts. Date codes on the parts indicated this unit was built in the mid 80's. Determined for the price I bought it for, I would go and refresh most of the typical failure prone parts of the unit. Replaced the rectifier diodes, the dried out filter caps, the 723 and TIP29, as well as the 2200uF cap on the board, and the pass transistors, as according to the test prescribed on the Repeater Builder's site, they were all bad. At $3.50 a pop, that was probably the most expensive part of the rebuild beside the 64000uF filter cap that the newer designs have (old design has two 50000uF screw top caps that aren't available. each is at least twice as big as the ONE cap that replaced both!). Some other assorted small bits got replaced too. Still came out far ahead, especially with the cost of shipping a heavy transformer style power supply to Hawaii. If it were a light weight switching one, it might be a different story... Plus I learned a lot in the rebuild :D

Hope your unit used a socket for the 723 chip, mine was old enough that it was soldered directly to the board. If you're good with an iron, its not a problem, but if not, the socket is a godsend. Whats the datecode on the pass transistors on your unit? It will be a four digit number on the silver things on the heatsink on the back. That'll give a rough date of vintage and help to find a schematic that matches your unit. Astron has made small changes over the years. Same general thing going on across the variations, but it can make looking at the schematic trickier when parts aren't what they're supposed to be.
 
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Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,732
10,715
823
58
Nova Scotia,Canada
I forgot all about the soldered in IC regulator. When I replaced the 723 chip in my Tripplet power supply I had to unsolder the old chip. I figured if I had to solder in a new one I would solder in a socket instead. I figured if I soldered in a socket to make it much easier to replace the next time I would never have to replace it again. ;)
 
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Happy_Hamer

Administrator
Staff member
Mar 22, 2001
5,061
185
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Well I unplugged the IC chip and plugged in the new one

I hooked up a CB with a pride 100 amp and it showed it drew 35 amps

It never shut down the radio or amp, but I never tried this cb set up before.

The radio I tried last week when I started this thread that would shut down, I sold on eBay

Now when I switch to the volt meter of the power supply I key up and the voltage drops to 12 volts from 14 volts on the meter.

I will hook up my volt ohm meter just to see how accurate the power supply meter is.

just being lazy right now. ^^ ab v c^^
 
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dxChat
Help Users
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  • @ ButtFuzz:
    on the connector with the green wire, if you short that to a nearby black wire, the power supply will turn on. (for use as a bench supply or whatever)
  • @ ButtFuzz:
    And IIRC, the purple wire is -12VDC, but that is from memory and it does not serve.
  • @ ButtFuzz:
    So if you need, say, 7v, connect + to the Yellow wire and - to the Red wire.
  • @ ButtFuzz:
    or or you need 9v connect + to the yellow wire and - to the orange wire. note: not all PSU's have the orange wire nowadays, as many manufactures had the voltage regulation on the motherboard, and all the power supply gives is 12 vdc
  • @ BJ radionut:
    Thanks ROB will check it out!~!! got to clean the work bench a little make room for that big case :)