POWERWARE PLUS18 UPS -AMAT SEMVision

  THE REPAIR STORY↓↓↓ 

1.0 PROBLEM STATEMENT
CB1 trips when switch-on. From AMAT SemVision system.

2.0 RESULTS OF INSPECTION AND PRE-SCREEN
No physical issue on visual check. Failure duplicated during testing.

3.0 DATA AND ANALYSIS
Below were the chronological findings and analysis during the troubleshooting.
Sketching schematic diagram on my own and signals tracing helps a lot.
a.) CB1 is the main input AC source circuit breaker.
b.) CB1 trips because its contactor coil is energized when switches on.
c.) The coil energizes because the +24Vdc coil supply is switched by mosfet.
d.) A surge signal is detected at mosfet gate every time CB1 switches on.
e.) An open collector output comparator delaying to pull down the mosfet gate.
f.) The comparator (V+) input signal and (V –) input signals are out of timing.
g.) (V+) and (V –) inputs are generated through different power source circuits.
h.) Found that (V –) switching transformer have slower response on switching CB1.
i.) That slow response causing timing issue resulting a surge signal at mosfet gate.
j.) Switching transformers are customized part and not available in the markets.

4.0 CONCLUSION
The (V –) signal delay triggers a voltage signal to trip CB1 when switches on.

5.0 SOLUTION
Customized switching transformer is not possible to replace. Thus, the workaround is to compensate the delay between (V+) and (V –) inputs of comparator. The RC circuit at V+ input had been modified to increase delay up to 3sec. This helps synchronize the slow signal from V– during powering-up. After modification the UPS works and has been running at production without any issues. Saved USD 17K!