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Author Topic: Astron 35A power supply problem---  (Read 422 times)
NU0R
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Posts: 408




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« on: April 30, 2007, 01:50:03 PM »

I have an Astron 35A that took a voltage spike from a nearby lightning strike. When I turned it on a few days later my radio would not come on. I checked the voltage out of the power supply and it showed 5 volts. I unplugged it and replugged it to re-set as per instructions. The problem is that now I show 20 volts output. I don't have a schematic so am flying blind. I don't see any obvious burn or char marks. Anyone ever have a similar problem? I would appreciate any input. Also where is the best place to get replacement parts. Also does anyone have a schametic they can e-mail me?   Thanks Bruce
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N3OX
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« Reply #1 on: April 30, 2007, 02:11:42 PM »

"Also where is the best place to get replacement parts."

I think there's nothing exotic in an Astron supply, so anywhere.  I like Mouser.

As for Astron schematics:

http://www.repeater-builder.com/astron/astron-index.html

Probably the 723 regulator chip, FWIW, and when I zapped my supply a number of years back, even **Radio Shack** still carried those.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W5EUT
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Posts: 19




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« Reply #2 on: April 30, 2007, 02:15:53 PM »

Try:

www.repeater-builder.com/astron/astron-index.html

73 Jim
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W6GF
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Posts: 161




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« Reply #3 on: April 30, 2007, 03:10:21 PM »

When I have fixed Astron supplies I have ordered parts directly from Astron.  Their delivery is fast and the price is good.

George, W6GF
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WA9SVD
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Posts: 2198




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« Reply #4 on: April 30, 2007, 03:28:07 PM »

Mouse, Jameco come to mind immediately.  The parts are quite inexpensive.
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WA9SVD
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« Reply #5 on: April 30, 2007, 03:29:13 PM »

Mouser, Jameco come to mind immediately.  The parts are quite inexpensive.
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K0BG
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« Reply #6 on: April 30, 2007, 03:44:38 PM »

Depending on the age and model, the regulator is either an 8 or a 14 pin DIP. The last ones I purchased cost a whopping 79¢.

BTW, this question comes up about every mouth or so. I did a quick search on the forum and got nearly 30 hits. It pays to use the search function.

Alan, KØBG
www.k0bg.com
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W5JE
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Posts: 17




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« Reply #7 on: April 30, 2007, 05:34:06 PM »

Dont't forget to check the pass transistors.   Ditto, order parts from Astron, especially if u need the pass transistors.   GL 73    Charles W5JE
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AA4PB
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« Reply #8 on: April 30, 2007, 05:54:42 PM »

I agree, it could be either one or more shorted pass transistors or the 723 regulator IC.
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AD4U
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« Reply #9 on: May 01, 2007, 07:40:29 AM »

My Astron 35 also has an SCR (crowbar) across the output to (hopefully) short the output and save your rig if an overvoltage condition happens.  Since you are reading 20V on the output it appears your crowbar protection was also zapped.  You might want to check this before putting the power supply back in service.
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K8AG
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Posts: 351




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« Reply #10 on: May 01, 2007, 11:53:46 AM »

I used to repair and design linear supplies for a living.  Problem might be the pass transistor(s).  Frequently a voltage spike will cause them to short and the output voltage simply goes up to the unregulated value.  Replacing the 723 may or may not solve the problem.

Usually you can check the transistors for a short C to E.  That doesn't guarantee that they are good, but it will show very bad ones.

Your crowbar circuit may also be toast.  It is supposed to clamp your output if it goes too high (so your radio doesn't join the destruct festival).  Sounds like it was trying to do that but if your pass transistors are shorted you can fry the crowbar as well.

Good luck.

73, JP, K8AG
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AA4PB
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« Reply #11 on: May 01, 2007, 02:40:07 PM »

I've experienced what I consider a design flaw in the Astron power supplies. A pass transistor shorted. The output voltage rose to 20+ volts. The SCR fired BUT it is directly across those large filter capacitors. The peak current of the SCR trying to discharge the capacitors caused the SCR to open. With 20+ volts passed on to the radio, several ICs in the radio failed.

The solution is to place a large fuse between the capacitors and the SCR/output. That way if the SCR fires, the fuse opens and the output goes to zero volts.
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NU0R
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Posts: 408




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« Reply #12 on: May 01, 2007, 02:43:59 PM »

K8AG , can I test the pass transistors with the wires hooked up to them or do I need to isolate them. Also I will have to admit that I have forgotten how to test them. Any info on testing will really be appreciated. I used to do building but that was 2 solar cycles ago. So far I think I will order the regulator IC and the thyristor (SCR crowbar IC.), and as many of the pass transistors as show bad upon testing. What is the Ic that is bolted to the bottom of the case? It is 3 legged, just lke the SCR on the regulator board.   Thanks a million, Bruce
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KH7N
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« Reply #13 on: May 11, 2007, 12:07:41 PM »

Aloha Gentlemen,

I too, have been out of the electronics troubleshooting community for many years, so I ask for your help.  My CAP wing has dozens of Astrons.  It is not financially viable to send them back to the mainland for repair, so when one goes bad it is returned to logistics, scrapped, and we don't get another one....budget cuts..I have here a nice looking RS35A which was powering a Motorola ALE HF rig for a short time.  Then the fuse blew in the power supply.  They sent it to me to look at because I am the metrology/calibration guy, but I'm not sure where to start. The the fuse doesn't pop under no load, it vaporizes.  I think the radio pulled the power supply way over it's rated duty cycle but I don't know what cooked off. It's my money but not my equipment, so I don't want to start shotgunning, but I'm sure I'll see this again someday. There are no burned components or smell. There were a couple of splashes of solder here and there but that might have been sloppy manufacturing.  I used to do this stuff with a Simpson 260 and now I'm using a Fluke DMM. Any assistance will be appreciated.
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