APC equipment - PDU AP7931 - Page 1
Forum section: electronics / repair

author: drkshadow
author_rank: Newbie
timestamp: April 08, 2025, 05:40:32 am
content: Hi all, after reading a thread on the APC 1500 firmware recovery (Thread 25), I was surprised and impressed and wanted to ask about a PDU too. :-)I have an APC AP7931 PDU. It had a power supply fault off-and-on, and then it had two, and died. I replaced the TOP244Y on the two power supplies, as well as the TVS diode (which was reading Open -- the icon on the PCB shows it just a regular diode, but it's not, so replace once, replace twice, read the schematic aaaand.. TVS).Anyway, in trying to figure things out, I took out the NMC and installed it again -- but i didn't notice the button was pressed when I put it back. So it was holding the "flip display" button for a couple weeks as I got parts and troubleshot the power supply. Something shorted to ground for too long for the flash to enjoy.End result, the power supply is fixed - no faults! - but the NMC is now broken. It doesn't register the second bank of switched ports (9-16), the MAC is all 0's (I can even set an IP *and* connect to it through a browser -- if I arp it it comes back mac 00:00:00:00:00:00 ;-) , and there's no serial or model number or revision for the system's About properties.From SE's site, it's now dumpster fodder and I should buy a new $1400 device to replace it .... but we know better. Yes the flash is broken, and it's only busted because they don't provide tools to fix it, but does anyone have some pointers? I can connect via serial and manage the app, but the closest I can get to setting a serial or MAC is setting the ClientID for DHCP properties. The AOS app just doesn't have this ability.I believe it's a NMC1 or NMC2, but clearly needs some device-specific configuration for the flash to function as a PDU. I don't have that.. it's lost. I've re-uploaded the rpdu app bin file (firmware part B), but no change.Model Number :Serial Number :Manufacture Date :Hardware Revision :MAC Address : 00 00 00 00 00 00Flash Type : AMD A29DL322DBIncluding two pictures. Unsure if JTAG or TTL serial would get me a lower-level interface than the front-panel serial port, or what I could do if it does. (I don't yet have a TTL serial device, I don't think.) Not sure what SW2 does (beside J5), seems to be nothing (not reset, maybe reboot)Any ideas?

author: BradC
author_rank: Super Contributor
timestamp: April 08, 2025, 10:00:54 am
content: I have an AP7952. I've not had the lid off yet, but the layout of the panel looks the same.I wonder if the config is stored in the program flash or its hiding somewhere else? The UI looks similar to my UPS and ATS and they are NMC2. The only NMC1 I have is an old AP9606 and I retired that last year for an AP9617.I need to pop mine open at some point because the current/load monitoring has gone way out of whack. Like the older Gen2/3 SmartUPS it would not surprise me if it was programmed through the serial port.If you come up with any tests or info I can help with I'm happy to poke around, but mine drives most of my back end stuff so I'd rather not pull it to bits if I can avoid it.Where did you dig up the schematic? I've got a pile of UPS schems, but nothing for the PDUs or ATSs (I have an AP7721 between the UPS and PDU)Oh, and apparently it's RS232 :https://www.luxnet.ch/computer/apccable.php

author: drkshadow
author_rank: Newbie
timestamp: April 09, 2025, 04:04:30 am
content: QuoteThe serial port can be mapped into the rj12 connector, I looked it up somewhere probably like what you gave. CH340 (flaky as..), and I can upload the APC OS(v3.9.4) and RPDU app via XMODEM protocol over serial. It's not quick, but it got the job done. It's probably NMC1 (max firmware 3.9.4), because I see firmware 7.1.2 for NMC2.The schematic was for the internal power supplies - they seem to provide power for the relays and the NMC card, at about 21v output. It's *nearly* the reference schematic from the TOP244Y datasheet. There are some differences. I don't have schematics or anything for the relay boards (which include a couple ICs, for unknown purpose - LED control? relay control?) or for the NMC itself. Additionally, the power supply looked to be exactly the same as the two in the ATS AP 7750A (I didn't check output voltage there, though).Monufacture date used to say: xx 2006.