Smart-UPS 1500 reboots instead of powering off

[Anonymous user]

Recently I've bought an old Smart-UPS 1500 that was on sale. It worked fine, but the fan noise along with the vibration was intolerable, so I decided to change the fan to something quieter. But because I am not the smartest person I didn't look at the voltage. Stock fan was 24V, 0.1A. New fan that I've bought is 12V, 0.15A.

I tried to plug it in. UPS powered on and immediately powered off and I think there was a spark. I switched the fan to the stock one, disconnected everything from UPS and turned it on. Now from what I can tell, it works as it should: I gave it a little load and ran self-test, which it passed, it holds the load as it should and it reports to the PC via USB as it should as well. But when I try to power it off (long hold the power button) it behaves differently. While I hold the power button it slows the fan down (which didn't happen before), when I release the button -- it speeds the fan back up. When I hold the button for 10 seconds, instead of powering off completely, the UPS shuts down and then powers right back up, like an insta-reboot. Other than that UPS seems to work fine. Again, it's an old UPS, so the warranty has been void for some time now. Should I take it to some third-party service center to take a look at? For now I've plugged out the battery connector on the back.