UPS 2200 - board went pop

[Anonymous user]

Hi. I have a 640-0735G Rev 7 main board with a blown cap which I'm endevouring to identify.

Its at label C34 on the board. Looking online I have found conflicting reports as to the specific cap eg 22uf, 16V or 22uf, 50V.

Needless to say I'd prefer to get the correct one!

Help would be most welcome.

Thanks

Martin

[Brad_C]

That is the bootstrap cap for one of the MOSFET high side drivers. My Schem says 16V, but when I re-worked a unit recently I used 50V as that is what I had on hand. That cap is going to see at least 12V, and in its role ESR isn't critical, so use whatever you can find.

Unusual for that cap to blow. It's not in a particularly stressed location. I'd have a close look at R38 and Q29/Q30 to make sure they're still happy. While you are in there, swapping R38 & R43 out for a pair of > 1W resistors isn't a bad idea either, although finding appropriately sized resistors with leads small enough to pass through the holes in the board isn't the easiest. Stand them off the PCB too. They tend to cook on that particular model and complete failure often means the bridge shoots through and destroys a handful of MOSFETs.

While your're replacing caps, do C35 also. Same role as the one that you are chasing, but on the other side of the bridge.

[Anonymous user]

Thanks Brad, checking as you suggested I note that R38 R43 all showing signs of heat discolouration.

C35 showing no signs but thanks for the tip.  

[Brad_C]

On 26/4/2018 6:34 PM, martin said:

C35 showing no signs but thanks for the tip.  

I'm not surprised. I've never seen one pop in that location before, but if you check both the capacitance and ESR I'd suspect you'll find at least one of them significantly out of whack.

[Anonymous user · Accepted solution]

Thanks again. I not that qualified to work on this myself so need to find someone who is.

Cheers

Martin