The unit is an APC BR1500MS "Back-UPS Pro 1500 S".
I recently purchased this UPS off of facebook market for a decent price, but I now believe I see why he was selling it! The UPS makes a faint whine. I've got the thing disassembled on my floor and used some silicone bendy straws in my ears (funny picture I know) to "search" for the noise origin. Initially I thought it to be a coil, but, it turned out to be the buzzer! This makes me think t hat there's something fishy with the circuit that drives the buzzer, or perhaps the DC power rail that it runs off of. I've also noticed the fan doesn't spin when I test the thing with a large load and the inverter transformer gets a bit warm. I don't see any small wire leads going into the transformer either so I don't believe it to be temperature activated. I ran my SMD rework station off of it to see if it was triggered by power draw, but that didn't do it either. I've also noticed that only 2 of the 4 Silicon power chips attached to the inverter transformer get warm, well actually, quite warm. The other 2 are arctic comparatively.
I've got a Rigol DS1054Z Oscilloscope (No current probes, sadly ) and a Fluke 87V DMM to diagnose this with.
But in writing this out and thinking about it, I wonder if the power transistor shorted out and is pulling a bunch of current from both the battery & the dc power rail which is why the buzzer is so noisly and fan doesn't come on. I'll have to check the output of it to see if I'm getting 120V sine wave & do a continuity test across the leads of the silicon power chips.
Will post some pics in a bit, but before then, anybody familiar with UPS design have any ideas?
I recently purchased this UPS off of facebook market for a decent price, but I now believe I see why he was selling it! The UPS makes a faint whine. I've got the thing disassembled on my floor and used some silicone bendy straws in my ears (funny picture I know) to "search" for the noise origin. Initially I thought it to be a coil, but, it turned out to be the buzzer! This makes me think t hat there's something fishy with the circuit that drives the buzzer, or perhaps the DC power rail that it runs off of. I've also noticed the fan doesn't spin when I test the thing with a large load and the inverter transformer gets a bit warm. I don't see any small wire leads going into the transformer either so I don't believe it to be temperature activated. I ran my SMD rework station off of it to see if it was triggered by power draw, but that didn't do it either. I've also noticed that only 2 of the 4 Silicon power chips attached to the inverter transformer get warm, well actually, quite warm. The other 2 are arctic comparatively.
I've got a Rigol DS1054Z Oscilloscope (No current probes, sadly ) and a Fluke 87V DMM to diagnose this with.
But in writing this out and thinking about it, I wonder if the power transistor shorted out and is pulling a bunch of current from both the battery & the dc power rail which is why the buzzer is so noisly and fan doesn't come on. I'll have to check the output of it to see if I'm getting 120V sine wave & do a continuity test across the leads of the silicon power chips.
Will post some pics in a bit, but before then, anybody familiar with UPS design have any ideas?