Electronics > Repair

Help to identify switching transformer for replacement

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This transformer (see image) is from an APC BR1000MS USP, and the secondary shorted.  I cannot find any information on what this transformer is, other than EE19 seems to designate a pin-out and size specification (I'm not really up  to speed on switching transformers)?

Any insight as to what the actual specifications of this transformer are would be greatly appreciated.  The UPS is dead without this since it powers the MCU and other control circuits, and of course I'm 2 months over the warranty.  The unit just died under normal conditions.

Text on the part from image in case there is a problem:

CLASS 130(B) SBI4.2
430-0843-Z  BCK-EE19-1571B
Jingquanhua NERE E208707

Why do you think it's shorted? SMPS transformer secondary winding resistance should be near 0 Ohm, not to say it would be extremely unusual for secondary winding to fail. Also SMPS transformers are custom made in 99% of cases.


What instrument to measure, VOM? RLC meter? Exact reading?

Most faults are due to shorted FETs or rectifiers.

99.9999% it is NOT the transformer


Meter is a Fluke 189, secondary is 0.008 ohms.  But after posting I did check the secondary for frequency and it shows ~55KHz, same as the primary.  DC average is 1V, AC average is 4V.  Primary side driver is a TNY278PN.

The resistance across the secondary rectifier diode (marked with "ON" in a circle (assume onsemi), M35 B320) is about 1.2 ohms in both directions, so I'll be removing it and confirm it has failed.  I'm also going to replace all electrolytic caps on the secondary side.

I will be very happy if it is not the transformer, since it seems that would be very difficult to find a suitable replacement.

Easier to take apart and rewind than find a replacement, I'd say.  Magnet wire is widely available, and the yellow tape might be 3M #56 or similar.

The TNY nearby suggests it's merely a flyback transformer for auxiliary supplies in the unit; tracing the circuit will yield what voltages it's producing.



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