BORRI 30kVA B8033fxs Uninterruptible power supply precharge relay fault

[SmartFoxElectronics]

Hi guys,

This is my first post, I thought I'd create an account here since I've started a new job and have far more time & freedom to investigate faults on the units I'm repairing, however, I've come from a job that dealt primarily in logic level electronics, to a job that builds, tests and repairs 3 phase industrial power supplies & have only been in the electrical field as a whole for 5 years so am by no means a veteran...

Anyways, I'm having a recurring issue on the charger/inverter modules of BORRI B8033fxs UPSs, on certain batches I get in, usually around one out of the 3 modules fails when I run them up through the test software it fails, giving me the fault code "042 precharge relay fault"

I've traced the control circuit itself to a couple of ICs on the far right corner of the PCB, but changing these does nothing, and for the most part the signals match up to those of a working unit.
Other things I have tried:

• Changing rectifier and inverter IGBTs
• Chaning the thyristors
• Changing DC BUS capacitors

This fault used to only occur in units that had been exposed to the elements & had seen corrosion but now seem to be getting more and more units that look relatively new giving us the dreaded precharge fault. It's a common fault that nobody else has been able to nail down, I'd really like to get to the bottom of it so I can stand out a bit to the bosses!

Any help would be much appreciated!

[trobbins]

Have you identified if the fault code relates to a specific digital input, or an analog trip level, or ...?

Have you identified the precharge relay that would be the subject of the fault code?  Is it just being controlled by a coil enegisation signal, or is their a state contact being fed back or an analog signal being fedback that would be directly related to the precharge function performing ok (ie. the capacitor being precharged reaches a set level within a certain time)?