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Author Topic: flakey power supply  (Read 213 times)
KG6SGP
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« on: April 11, 2004, 01:25:23 AM »

Here's what procrastination gets you.  :-/

Executive summary:   any idea what would cause a power supply to only provide juice sporadically, and usually only after it's been on for a while?  Anything I can try probing with a voltmeter?

Long version:

I bought a 25amp SEC power supply at the local Fry's electronics.  When I got it home I found it wasn't putting out any power.  No fuses blown, everything seemed to be OK, but no juice.  So I took it back and returned it.  The guy came out with another of the same.  This time I wanted to make sure it worked before I schlepped it home.  Powered it up and he put a voltmeter on it.  Nothing.  Powered it down, powered it up, tried again, no joy.  Powered it down, got a different voltmeter, powered it up and it registered proper voltage.  I chalked it up to the voltmeter he was originally using.

I got it home, powered it up ... nothing.  Grr.... I let it sit there while I pondered what to do next and then suddenly it started putting out power.  Now at this point, I should have taken it back, but I was tired and didn't feel like dealing with the returns line again.  It was working, so I left it.  It ran great all day.  I powered it down, then tried powering it back up.  Nothing.  I let it sit there and after about 2 hours it started putting out juice again.  OK, definitely should return it - put that on your todo list.  Todo list never gets todone.

I continue to use the supply.  It works fine once it starts putting out juice, but sometimes it takes a while for it to work.  Sometimes 10min, sometimes several hours.  I then got in the habit of leaving it on all the time and that worked fine.  But today I had to power it down to work on some stuff and when I tried powering it up ... nothing.  Let it sit for about 4 hours, still nothing.  Now I'm getting really frustrated but it's a fair bit past the 30day return policy.

so any ideas what might be causing this, how I might debug it and hopefully fix it?

Thanks,
KG6SGP
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N3JWN
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Posts: 103




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« Reply #1 on: April 11, 2004, 07:43:18 AM »

First of all whats a 25amp SEC power supply Huh?Transformen analog or switching type??
Dick / n3jwn
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K1CJS
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Posts: 6012




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« Reply #2 on: April 11, 2004, 11:34:22 AM »

If you open it up you may find bad or cold solder joints or poor and intermittant contacts on some connections.  JUST BE EXTREMELY CAREFUL--the capacitors inside hold a large, powerful charge--enough to send you flying across the room.  If you touch the wrong thing while the caps are charged you may not be around anymore.

If you know what you're doing, while the supply is open turn it on with a voltmeter attached to the output.  Use a plastic rod and wiggle the connections inside.  More than likely you'll find the things I mentioned somewhere in there.  Use the one hand rule--put one hand in your pocket and use the probe with the other.

If you're not sure, have another ham who is more knowledgeable do this for you.

Chances are the discount chain you got this supply from got the lot from a company that offered them at a discount because of problems like this.  Happens all the time, and the consumers who are looking for a bargain get burned.
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K5LXP
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« Reply #3 on: April 11, 2004, 01:01:43 PM »

Some switching supplies depend on having a load upon power up for proper regulation.  Try putting a light bulb on it and powering it up a few times to see if it becomes more consistent.

Mark K5LXP
Albuquerque, NM


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W5WJP
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« Reply #4 on: April 11, 2004, 04:57:51 PM »

The key here is Fry's. Seems like everything I have bought from them, I have had to return. I think they get a "good deal" on factory returns.
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W3JJH
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« Reply #5 on: April 12, 2004, 12:12:44 PM »

Why not give Samlex a call and ask for help?

(800) 561-5885
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