Please help me repair power supply

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nozit7022

Joined Aug 2, 2015
1
Hi, good day. I'am electrician by profession. I would like to explore on the electronic side. I'm trying to repair the power supply but i'am stuck. There is no output voltage. I check on the bridge diode and there is output until in the primary side of the transformer and no on the secondary. Attached the pics of power supply. I hope you have time to help me. Thanks and GOD BLESS
 

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bwilliams60

Joined Nov 18, 2012
1,177
What is the voltage (DC) across the large cap? What is the voltage coming in and the voltage on the primary side of the transformer?
 

Dodgydave

Joined Jun 22, 2012
8,375
What you have there is a switchmode psu, the Top227 is an ic, and if its blown up it wont work, you need to measure the voltage on the chip.
 

Hypatia's Protege

Joined Mar 1, 2015
3,197
there is output until in the primary side of the transformer and no on the secondary.
Please be advised that the pictured PSU is an SMPS -- Your DMM/VOM may not be responsive or accurate at the (switching) frequencies/waveforms involved... --- You are best advised to focus upon DC measurements (electrolytic and other high-value capacitors being convenient test points)...

Best regards and good luck!:)
HP
 

ian field

Joined Oct 27, 2012
6,543
What you have there is a switchmode psu, the Top227 is an ic, and if its blown up it wont work, you need to measure the voltage on the chip.
I'd advise against poking about with DMM prods - those Power Integrations chips can be a bit temperamental. They have a bit of a tendency to blow a crater in the plastic encapsulation when they go bang.

First I'd test/replace all/any small electrolytics as routine maintenance.

Very often a shorted secondary side rectifier shuts the PSU down, but I'd examine any power resistor between the chip and the negative of the reservoir electrolytic. Sometimes that blows open before the chip explodes.

There's usually a high resistance start up resistor that can go high or open.
 

#12

Joined Nov 30, 2010
18,076
From what I see on these blurry photos the main switching transformer is burn.
That yellow transformer looks burnt on its bobbin, but the photo is rather poor quality. I can't be sure.
 

hp1729

Joined Nov 23, 2015
2,304
Hi, good day. I'am electrician by profession. I would like to explore on the electronic side. I'm trying to repair the power supply but i'am stuck. There is no output voltage. I check on the bridge diode and there is output until in the primary side of the transformer and no on the secondary. Attached the pics of power supply. I hope you have time to help me. Thanks and GOD BLESS
Attached is a data sheet for the TOP227. The schematic on it may be similar to your power supply.
 

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