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Electronics => Repair => Topic started by: OpenCircuit on March 26, 2017, 03:58:58 am

Title: DC-to-DC Transformer Testing
Post by: OpenCircuit on March 26, 2017, 03:58:58 am
I have a switching power supply from a desktop computer. PSU keeps shorting one particular MOSFET and the fuse, so I pulled the DC-to-DC step-down transformer for testing. The MOSFET that keeps shorting is the one that made the burn mark on the transformer. I have continuity across all row A terminals and continuity across all B terminals and no continuity from A to B.  Does this indicate a properly functioning transformer? I have reviewed the fundamentals of transformers, but I would rather ask before I conclude.

(http://i1362.photobucket.com/albums/r696/markingIT/PSU/IMG_0503_zps0nqogh24.jpg) (http://s1362.photobucket.com/user/markingIT/media/PSU/IMG_0503_zps0nqogh24.jpg.html)


(http://i1362.photobucket.com/albums/r696/markingIT/PSU/Transformer_zpsaxymm1ga.jpg) (http://s1362.photobucket.com/user/markingIT/media/PSU/Transformer_zpsaxymm1ga.jpg.html)


Title: Re: DC-to-DC Transformer Testing
Post by: Armadillo on March 26, 2017, 05:08:26 am
Your test is inconclusive and incorrect.

Firstly identify the primary coils and the secondary coils, you can either trace from the circuit boards or if you have the service manual then refer to the schematic or refer to the manufacturer datasheet for the transformer which is the best. Identify the primary coil, auxiliary coil and secondary coils.

Take the coiltransformer out from the circuit - Measure the dielectric breakdown between the coils. This measurement should indicate infinity ohms.

then you either RING the coil or measure the inductance of the coils to detect internal coil shorting that alters the inductance beyond acceptable tolerant. Primary Coil failure rate is always the highest.

The answer above is limited to reply to the subject question only, specifically DC to DC transformer testing.