APC BE650G2-UK surge strip UPS - not powering?

[spleenharvester]

I bought this UPS as nonworking. Annoyingly they did not mention the battery has been removed so basically a waste of money... but it's here now so I'd might as well do something with it.

The device shows no signs of life when connected to mains. If I connect a lab supply to the 12V battery terminals it powers up, and flashes the LED showing it is running on backup power. However when mains power is then applied it doesn't seem to do respond in any way. So presumably if I put an actual battery in there it would just make no attempt to charge it, it would discharge and then the unit would go back to being dead again.

I'm going to get stuck into it this evening but any tips on where to start looking would be appreciated. I've checked all the basics like the schottky diodes and they are all OK.

[CapLeaker]

Yes, it is. It first checks the battery, then it checks if main power is present. If main power is present, it will switch to main power. Unless there is a problem with the detection circuit like it was on my SUA1500.

[spleenharvester]

Pics. Ignore the missing resistor, I had a daft moment and removed it thinking it was shorted.

Have just confirmed 230V is present at the cable from the inverter board to the mains board so it looks like the fault is on the mains board

[spleenharvester]

Ok weirdly I just reassembled it and it seems to be working now. Will come back if anything changes. (I wonder if that R750 I removed was in fact shorted?)

[CapLeaker]

Resistors usually don't go short. That only happened to me once in my whole repair career.
While there is that exact phenomena that you are experiencing, you can read up on one of my attempted repairs and see what I found at the end.
https://www.badcaps.net/forum/troubl...-turn-on/page3
Problem ended up being an open transformer winding in the primary side. The T1 transformer was responsible for the whole voltage sense circuit. Also there is a schematic to boot so you can see how that unit worked.

[spleenharvester]

Oh interesting, yeah mine was making a bit of an odd noise from somewhere too. Transformers are reading OK though. I ordered a battery anyway so time will tell if it was just a fluke.

[spleenharvester]

Ok the battery is here, I think the "fault" was actually just confusion with how it works - if the UPS is powered on by the power button while mains is plugged in it seems to run for about 30 seconds from battery before the device acknowledges mains is present and starts charging. I am guessing this is actually normal behaviour.

[CapLeaker]

Yes, it is. It first checks the battery, then it checks if main power is present. If main power is present, it will switch to main power. Unless there is a problem with the detection circuit like it was on my SUA1500.