I am diagnosing a 22 year old UPS (APC 1400RM) problem, the big transformer (430-7140A) is getting very hot yet the UPS works and self test reports fine. I suspect something is going to fail soon and destroy some parts, so I want to diagnose and replace a failing part to prevent disaster.
I suspect the windings of the transformer may be starting to short (not enough to cause outright failure, but I can smell the varnish melting and it is VERY hot to touch). I have an inductive ammeter which I thought might help me diagnose this.
I can't find the transformer in the circuit diagram so I'm trying to understand what it does. On one side there are 2 thick wires which attach to (heat sink) plates connected to transistors. on the other side are 4 thinner wires which go to the circuit board. Would wire size tell me which side is primary/secondary? Next, is it possible to use my inductive ammeter to determine if it's starting to short? Again, it's still functional so I don't expect a 0 ohm short...
I can't find any specs on this transformer as I suspected it was made exclusively for APC. Is there another test I can do? (capacitance or resistance which might indicate a problem?)
(I checked the caps while still in the circuit and none are shorted, and none are swollen).