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Computer switch mode power supply suddenly fails

Proschuno

Aug 1, 2011
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So suddenly my power supply ( switch mode) stops working. Now I notice whenever I would try to sink to much current from/they it, it shuts off as a safety feature. Knowing this, and my insane mind lol, I've triggered this to many times to count. But now it won't even turn on, and I'm not in the mood to spend $$$ on a supply. I know this is quite vague, but where do I even start diagnosing?
 

grant1842

Oct 1, 2012
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I have worked on computer SMPS.(ATX, etc)

Most often i find bad caps, and all so the Bridge rectifier.

Start by taking it apart. Check the fuse.
If the fuse is blown then be sure to check the Bridge Rectifier for short.

If the fuse is NOT blown then most likely CAPS.
Look at the caps I bet you see some swollen CAPS (secondary side) .

I have seen the switching transistors all so short to ground and blow fuses .
Some have MosFets for switching. so check them as well.

If you need help on how to test the single package bridge rectifier let me know I will show you.

P.S If you have not worked on SMPS before then you need to learn how to bleed the Primary filter CAPS(THe Big Ones).
Safety first.
 
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Proschuno

Aug 1, 2011
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Sorry I also forgot to say that it's from a Macintosh g5 if that rings a bell for anyone. I'm not finding anything that would seem to be a rectifier..... All I'm finding near the power input is capacitors and a toroidal transformer. Also no bad fuses or caps. Would it be whatever prevents excessive current flow, like a thermistor or something?
 

Proschuno

Aug 1, 2011
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Model is PCF451601A... I'm using an iPad so I can't post pictures.
 

grant1842

Oct 1, 2012
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Well usually dead with a good fuse you need to test , Bridge Rectifier, Power Fets, secondary Diodes, etc.

If after checking these items and still no luck its time for some live voltage testing.
If you do not understand how a SMPS works it is dangerous to do voltage testing.

There is a Hot side and a cold side . Probing the wrong ground with the wrong side will get a big blue flame and ruin your DVOM :).

I hate to guide you and you get hurt.

Safety first . If you have not done live voltage testing on a SMPS before then do not try this.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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There is a Hot side and a cold side . Probing the wrong ground with the wrong side will get a big blue flame and ruin your DVOM :).

Or give your family the opportunity to attend your funeral.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Look for a shorted rectifier diode, or possibly dead filter capacitors.
 

djradu

Oct 5, 2012
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So suddenly my power supply ( switch mode) stops working. Now I notice whenever I would try to sink to much current from/they it, it shuts off as a safety feature. Knowing this, and my insane mind lol, I've triggered this to many times to count. But now it won't even turn on, and I'm not in the mood to spend $$$ on a supply. I know this is quite vague, but where do I even start diagnosing?

Every electronic gear has its limits,pushing something over does not bring any good,as in this case "playng" with the source "killed" it,the fact that has a over current protection does not make sence to blow it.Have you checked the FUSE,it has to have one,the protection circuit may be damaged and needs replacing,the crowbar circuit ( even if its for overvoltage needs to be tested,
http://en.wikipedia.org/wiki/Crowbar_(circuit)
http://power-topics.blogspot.ro/2008/09/over-current-protection-in-power.html

Check the 2 links
 
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