Repair APC SMT1500, blank screen - Page 1
Forum section: electronics / repair

author: pronichkin
author_rank: Newbie
timestamp: March 15, 2025, 09:53:41 pm
content: Hello!A while ago I purchased a used SMT1500 from eBay. It arrived seemingly functional, in the sense that the screen was operational, it responded to various buttons pressing, etc. Also, there was power output while plugged into the wall. But it was complaining about the battery being dead. So, I purchased replacement batteries, also from eBay.I did replace batteries in another UPS once, so I thought it would be an easy task. However, once I connected new batteries, assembled everything, and tried to power it on, the UPS just died, apparently. Now whenever I plug it into the wall, it beeps, the screen lights up, but there's nothing on the screen, and it does not respond to any buttons being pressed. (And of course, there's no power output.) This happens even if I power it on without the batteries, or with cutoff switch disengaged in the back.I have no experience diagnosing this type of hardware, but I naively suspected that maybe it's just the screen control module what's broken. So I purchased a replacement (640-1171A-Z) board. It arrived yesterday, but replacing this module did not seem to change anything.The cable from screen control module goes directly into the main PCB (640-3081A_REV06). So, I now suspect that maybe replacing that one could help. But it costs another $100 plus delivery fees, and I'm not even 100% sure I can successfully replace it myself. (I know how to hold the screwdriver and can occasionally do minor repairs to PCs and such, but I'm nowhere near being an electrical expert.)So what would you recommend? Should I give it a go? Or there are other, more reasonable troubleshooting steps I should try first? Or do you think it's not worh it at this price point, and I should just give it away to recycling, and maybe try my luck buying another UPS?

author: CapLeaker
author_rank: Regular Contributor
timestamp: March 16, 2025, 06:40:15 pm
content: Try reseating that cable that goes from the screen and buttons to the main board. These things can come loose during shipping and not only on this style UPS.

author: pronichkin
author_rank: Newbie
timestamp: March 16, 2025, 07:25:08 pm
content: Thanks for suggestion! This was one of the things I checked when replacing the display control module. Unfortunately, that did not help. Also, the lack of power output suggests that the problem is not with the display.

author: CapLeaker
author_rank: Regular Contributor
timestamp: March 16, 2025, 07:59:15 pm
content: Did you check the connection on the display board too?

author: pronichkin
author_rank: Newbie
timestamp: March 16, 2025, 08:02:34 pm
content: Yes, I did replace the whole display board. While doing that, I checked the connection at both ends. (Unplugged the cable and then plugged it again firmly.)

author: asis
author_rank: Frequent Contributor
timestamp: March 17, 2025, 11:32:03 am
content: Hi,Start by checking your charger.-If you used a deep discharge battery purchased at auction, it is possible that the charger is faulty.https://www.eevblog.com/forum/repair/apc-smt1500rm2u-ups-only-blinks-and-beeps-when-plugged-into-mains/https://www.eevblog.com/forum/repair/apc-smt3000rmi2u-battery-not-charging/

author: CapLeaker
author_rank: Regular Contributor
timestamp: March 18, 2025, 01:20:04 am
content: What does the UPS do unplugged, batteries installed and you press the on button?