Electronics > Repair
Repair Help for APC UPS BR1500G - F06 error (FIXED!!)
fmashockie:
Well guys I have another update with this UPS... It's fixed!!! :wtf: Well not exactly...
So I am waiting for the delivery of the UART-USB adapter and the new micro so I can flash the chip. But today I decided to test the AVR function of the unit a bit more. A few things I found out:
RY14 = Boost relay (this is the relay I discovered that was always off and was not getting a high input to the base of its controller transistor Q63)
RY12 = Buck relay (more about that later)
Boost mode = RY14 is on, RY12 is off
Normal mode = RY14 on, RY12 on
Buck mode = RY14 is off, RY12 on
So I decided to test the unit in boost mode. I started bringing the input voltage down from 120VAC while injecting ~1V at the base of transistor Q63. Once I got down to ~100VAC, the unit was in boost mode and it automatically triggered the F06 error. So this meant there's something wrong with the buck relay (RY12) as well - it was not turning off once the voltage got low enough for boost mode! The transistor that controls switching to RY12 is Q57. I traced it back to the micro and it is connected to pin 27 which is another GPIO pin (PB14). This is right next to the pin that ties to the base of Q63 for the boost relay RY14 (pin 27 PB13). I have attached a layout of the micro and descriptions of pin functions.
What I also discovered is that pin 27 is shorted to the VDD pin! I checked to see if there's anywhere else that this short could be occurring but could not find it (will continue looking). Please correct me if I am wrong, but none of the GPIO pins should be shorted to a VDD pin right? I was thinking this should be another indication that the micro is bad (maybe?). But I decided to do a bit more experimentation and so I shorted the bases of Q63 and Q57 together with a 0 ohm resistor to see if the UPS would work under normal voltage (120VAC) conditions and it does! So for that reason, it is fixed somewhat right?? :-DD
Curious to hear if anyone has thoughts on this and/or if this new info changes anyone's ideas on the micro being bad?? Is there some other part of AVR circuitry I should check/test? Regardless, I'm really excited to try to flash the micro once I get the stuff I ordered. Here's a video below I did on these findings. And as always, really appreciate everyone's help so far!!!
BradC:
If I didn't know any better (and I don't!) I'd say it almost looks like the micro thinks it's on a board that doesn't have AVR.
I have no experience with later units than the late 4th Generation SUA units, but on all the APC units I've worked on, a firmware setting held the device type. I had once instance where the eeprom on a unit ended up corrupt and a 230V 50Hz unit believed it was a 110V 60Hz unit. All sorts of weird things happened.
I find it hard to believe you have a fully functioning ups *except* for hardware failures on both boost/buck relays simultaneously. One duff output perhaps, but for both to go with the rest of the unit performing normally sounds pretty remote to me.
RLP:
I don't know much about the internals of microcontrollers or their failure modes - but a GPIO being shorted with low impedance to a supply rail while the MCU is off, does sound like evidence of an internal problem. The two pins in question are next to each other and on the same port (PBx), so I guess there is some possibility of a common cause for the failures.
Random thought: relay coils produce voltage spikes, which are usually clamped by diodes in the relay drive circuitry. Have you tested the diodes on those two relays? My thinking is: flyback diode fails -> back EMF from relay switching not clamped -> propagates through circuit and does damage to the MCU. It'd probably kill the relay drive transistors first though... did you mention that one may have been faulty?
I did have a microcontroller once where the entire ADC section failed, so all of the ADC inputs would read high values (as if the internal voltage reference was low), unless at least one ADC input was connected to a low-impedance voltage source such as VDD, then the remaining ADC inputs would read correctly. The rest of the microcontroller was fine, so reading firmware/replacing the chip/flashing fixed the problem. I never figured out what caused the problem, my only conclusion was that weird stuff can happen inside microcontrollers!
fmashockie:
--- Quote from: RLP on September 06, 2023, 07:33:35 am ---I don't know much about the internals of microcontrollers or their failure modes - but a GPIO being shorted with low impedance to a supply rail while the MCU is off, does sound like evidence of an internal problem.
--- End quote ---
Yep this is exactly what I am witnessing (should have been more clear). This is with the mirco off and power disconnected from the board. Still measuring short between PB14 pin and VDD pin. That's gotta be a hardware failure of some kind right (whether on the micro or elsewhere)?
--- Quote from: RLP on September 06, 2023, 07:33:35 am ---Random thought: relay coils produce voltage spikes, which are usually clamped by diodes in the relay drive circuitry. Have you tested the diodes on those two relays? My thinking is: flyback diode fails -> back EMF from relay switching not clamped -> propagates through circuit and does damage to the MCU. It'd probably kill the relay drive transistors first though... did you mention that one may have been faulty?
--- End quote ---
Interesting thought. So I did replace the internally biased BJT (Q57) and it's zener diode which connect to RY12. This was prior to having a better understanding of the circuit. I just thought they were measuring a bit lower forward bias voltage during diode test - turns out it was normal. But I will replace Q63 and D68 for RY14 just in case. I know it won't fix the problem, but just to prevent any damage to the new micro. Thanks for your continued help on this RLP - I greatly appreciate it!!!
--- Quote from: BradC on September 06, 2023, 04:25:46 am ---If I didn't know any better (and I don't!) I'd say it almost looks like the micro thinks it's on a board that doesn't have AVR.
I have no experience with later units than the late 4th Generation SUA units, but on all the APC units I've worked on, a firmware setting held the device type. I had once instance where the eeprom on a unit ended up corrupt and a 230V 50Hz unit believed it was a 110V 60Hz unit. All sorts of weird things happened.
I find it hard to believe you have a fully functioning ups *except* for hardware failures on both boost/buck relays simultaneously. One duff output perhaps, but for both to go with the rest of the unit performing normally sounds pretty remote to me.
--- End quote ---
I hear what you're saying BradC, but I don't see how this could possibly be a firmware issue. I didn't do ANYTHING to this unit/board. It was in service for ~3-4 years, then I took it out service briefly/put into storage, then I took it out of storage once to take a look internally to help troubleshoot another UPS, then put it back into storage for several months, and finally took it back out recently and it started with this fault! Did not make any modifications to it or anything. It always worked fine until now. So I really doubt this is a firmware issue. It has to be a hardware fault of some kind. But I appreciate your input!
Vovk_Z:
It looks like a hardware issue but APC UPS are known to have software problems too, e.g. loosing calibration parameters or even totally loosing all settings (230/115 V and/or 50/60 Hz etc). I've seen it on one of my UPS when smal electrolytes became a bit 'weak' (charging voltage became 24VDC instead of 27.6 VDC).
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