Author Topic: SMPS FAILED, feedback wanted.  (Read 913 times)

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Offline The_Todd

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SMPS FAILED, feedback wanted.
« on: September 07, 2017, 01:29:21 am »
Hello guys,

Just after a bit of wisdom about this power supply.

So its completly dead with blown fuse. Now if you look at the tracks near (i think) the secondary winding for the IC power supply, the has been a serious short curcuit. Now im getting pretty good at fixing these but this puzzles me a little. What would cause this? Perhaps a short in a voltage divider or diode.

Its a HMI power supply used for industrial use, so thesegenerally arent a dodgy design. Also im not too fussed about fixing it, this is just spare parts that I work on to learn.

Cheers,
 

Offline The_Todd

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Re: SMPS FAILED, feedback wanted.
« Reply #1 on: September 07, 2017, 01:32:36 am »
here are some pics, also should note this is after some very light ultrasonic cleaning.
« Last Edit: September 07, 2017, 01:34:07 am by The_Todd »
 

Offline Armadillo

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Re: SMPS FAILED, feedback wanted.
« Reply #2 on: September 07, 2017, 02:22:37 am »
my 2 cents;

I would consider this as catastrophic failures, sudden and at large current meaning a dead shorts so severe that the protection networks didn't have the time to capture it.
Mosfet  or the Output schottky diodes short circuit or the pmic chip itself, In this case, the review sign indicates high percentage that the schottky diodes dead shorted.

Just my opinion.  :)

 

Offline The_Todd

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Re: SMPS FAILED, feedback wanted.
« Reply #3 on: September 07, 2017, 02:40:23 am »
hey, looks like you may be right, reading the schotty diodes (2 3-pin types in parallel) I get very weird reading in biased and reverse biased testing. so if these are shorted, shouldn't it burn out the terminals on the secondary side? how does it effect the secondary winding on the primary side?

also lucky i don't want to fix this, they actually pop-riveted the schottys onto the heat sink :S

cheers.
 

Offline CJay

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Re: SMPS FAILED, feedback wanted.
« Reply #4 on: September 07, 2017, 06:34:37 am »
i'll have a go at repairing all sorts of things because it gives me a kick to fix things other people have rejected as too hard or scrap but I'd not bother with that one, too damaged, too cheap and not interesting enough to be fun.

Riveted on devices aren't an issue, they're more common than you might think and in some high price items too, pop riveters are cheap and it's trivial to drill rivets out.
M0UAW
 

Offline Armadillo

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Re: SMPS FAILED, feedback wanted.
« Reply #5 on: September 07, 2017, 07:06:25 am »
hey, looks like you may be right, reading the schotty diodes (2 3-pin types in parallel) I get very weird reading in biased and reverse biased testing. so if these are shorted, shouldn't it burn out the terminals on the secondary side? how does it effect the secondary winding on the primary side?

also lucky i don't want to fix this, they actually pop-riveted the schottys onto the heat sink :S

cheers.

Catastrophic failure meaning it will take many things with it, likely the fuse, mosfet will be destroyed with it on the primary side. The secondary winding may just survive but not sure. You can ring test it if you are curious enough. I don't think its cost effective to repair this one. Concentrate on your hung chang more worth the time, simple horizontal amplifier to CRT coil.  :)
 

Offline The_Todd

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Re: SMPS FAILED, feedback wanted.
« Reply #6 on: September 07, 2017, 09:19:54 am »
Haha yeah, the scope looks like my next big project lol
 


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