Electronics > Repair
Help to identify switching transformer for replacement
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fmashockie:
These units are crap anyway.  I'm surprised to see one with a SMPS failure though.  I've repaired a few APC BR1000 units and usually the pure sine wave models have a problem with the large AVR/inverter transformer.  They are destine to fail right from the start.  I've done videos on my YT channel repairing these and HI-POT testing the large AVR transformers.  For some reason, the BR1000MS (pure-sine wave models) are the worst.  I've tested them brand new and they will fail HI-POT test.  If you get one of these bad transformers (or if they go bad over time) it will eventually short the inverter MOSFETs - usually when you need it most such as when it is switching from mains to battery backup.  It can fail in spectacular fashion, too.  The 40A fuses that are there to protect the battery don't doing either to help either (never find them open after this failure).  However, you can repair them and get them to last a good while as long as you replace that large inverter transformer with a different make.  I've used ones from the APC simulated sine wave models and then it works just fine.  For some reason they are made better.

Failure likely isn't with the SMPS transformer.  Take a look at the TNY278PN and its datasheet.  If you have a scope you can check to make sure it is switching properly.  You can also use your meter to check it as well.  Check for ~5.85VDC on the BP/M pin.  If it drops below, 4.9VDC the internal MOSFET is not switching.

That SMPS outputs ~24VDC and then it gets stepped down to 5V and 3.3V for the microcontroller
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