Compaq T2400h UPS Repair Advice

[maxwin]

Hello !

I have a Compaq branded UPS, model T2400h.

It's making curious unhappy rattling noises when running on battery.
Batteries are brand new and fully charged, and also tested on another identical unit.

I grabbed a video of the noise (starts at 00:18 on the mp4 video at the Goo link below), and also took a couple o'scope shots of the waveform, both on-mains and on-battery.

The scope connection is via a small 12VAC transformer, just to explain the scaled voltage readings in the scope photos. We are on 240V-ish mains here.

Would anyone recognise the noise, and be able to speculate as to the source ?

Such a nice UPS, and would love to save it!

All the photos, video and docs here: https://drive.google.com/drive/folde...IgEtLIrMhmc_88

I will try to attach the scope captures here too!

Thanks for this forum to let me ask here!
Max.

[maxwin]

Re: Compaq T2400h UPS Repair Advice

The video was quite a large file, so I trimmed to 5 seconds of noise and saved to a smaller (4.5MB) file.

https://drive.google.com/file/d/1FSY...usp=share_link

I'm thinking it might be some sort of "out of phase" situation that's causing the transformer coils to rattle. Maybe one of the NPN/PNP gate drive transistors is not at full health, and it's driving some of the power mosfets out of sync to the others.

That's a wild guess, and so hard to work without a schematic!! Gosh, I wish Compaq shared all their old schematics and service docs, so save the world having to scrap so much hardware!

I might try removing/testing/replacing all the transistors and see what happens.