Electronics > Repair
Repair Help for APC UPS BR1500G - F06 error (FIXED!!)
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fmashockie:
Hi RLP.  Hmm that is a very good point.  I just assumed that with the BR1500G that the large transformer was being used for both the inverter and AVR just like the BR1500MS2.  However, the BR1500G is the simulated sine-wave model and the BR1500MS2 is the pure sine-wave model.  And I've always wondered what that large transformer on the PCB was for so I think you might be right.  I suppose is it is still too early to be jumping to conclusions.  It's just with the exception of that internally biased BJT (still not sure if it was bad or not), I didn't really find anything that stood out on the controller side for the relays that would indicate a fault.  And even though they employed a lot of cheap electrolytic caps (OST, CapXon, Chang, etc), none of them really measured that poorly once I got them out of circuit.  Still replaced them though.  Can't wait to get these remaining parts in to see what happens.  I just thought it was interesting to share.  Really appreciate your input on this.  Thanks again!!
fmashockie:
The BR1500G saga continues.  I received all the replacement components I ordered (all the MOSFETs and that internally biased NPN BJT by one of the relays).  I soldered them all in and fired the unit up and of course... it's still having the same issue  |O When the input voltage is ~120VAC, I start it up, it does its self-test (switching from battery to mains and back), and then I hear another relay click, and then it triggers the F06 error.  After that, I increased the input voltage to >130VAC to force into AVR mode, and it was working without triggering the F06 error.  But as soon as I brought the voltage back down, the error was triggered. 

But then something else happened.  I was running it in backup battery mode (using my DC supply to limit the current) so I could make some measurements.  The unit will beep every 30 secs or so to let the user know its on battery.  All the sudden, the buzzer got much louder.  I decided to check the input voltage and supply voltage on a nearby LM317T and LM358 and they had increased by ~10VDC!  It stayed this way for ~1 min. Then the buzzer got lower, and all the sudden the unit powered itself off.  I couldn't get it to start back up via the display controller after this happened.

I took some measurements. The ~24V rail (it usually sits at 26-27VDC) was ramping up and down by ~1V every 500msec or so.  The 3.3V rail was doing the same.  I have attached photos of the waveform for these measurements from my oscilloscope.  Any thoughts on what could be causing this? Or where I should begin to look for faults? I'm not sure if I've caused another issue or just made the original worse (i'm hoping its the latter).  Thanks in advance!!
Vovk_Z:
I'm not sure 3V3 rail is ok. Are you sure you are doing measuring right? It mustn't have such a pulsations I guess. Are you sure you have replaced all electrolytic caps?
fmashockie:

--- Quote from: Vovk_Z on August 29, 2023, 08:34:08 am ---I'm not sure 3V3 rail is ok. Are you sure you are doing measuring right? It mustn't have such a pulsations I guess. Are you sure you have replaced all electrolytic caps?

--- End quote ---

Yes I know the 3.3V rail is not okay.  None of the secondary power rails are okay.  They should not be ramping up and down like this.  And it is definitely a problem because now the unit will not even turn on.  That's why I was asking for help!!  And yes I'm confident I took the measurements correctly.
RLP:
From your description I'm thinking an onboard power supply failed in some way, and put out an abnormally high voltage, as you measured - and then some downstream component, maybe an IC or another power supply, failed due to that overvoltage. The failed component probably went short, hence it all shut down and won't power up. The ramping behavior you see might be power supply 'hiccuping' where a power supply is shutting down due to overcurrent, then restarting, then the cycle repeats. 500ms to a couple of seconds sounds about right for that.

If that is the case, I would say you need to find the shorted component. One idea is to try powering it up again and see what gets hot. Another approach is to measure the resistance of various rails to ground (3.3V, 12V, etc.) and see if one is obviously shorted, and then inject a controlled current into that rail from an external power supply and measure voltage drops across PCB traces on that rail to locate the fault.

If you remove the shorted component and power it back up and there is still a power supply issue, the overvoltage condition might come back and cause more damage! So the root cause is important too. This is kind of familiar to me because I had a similar thing happen when I was working on a UPS once. In my case it was the main 12V power supply of the unit, which went up to about 25V! It turned out to be because I'd damaged a resistor in the feedback loop of a switching regulator, while soldering a probe to it to measure the voltage, and it was a complete distraction from the main problem I was troubleshooting on the UPS. I had to replace a few ICs and fix the power supply - but it was alright in the end.

Good luck!
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