Smart UPS 2200 stopped working

[Anonymous user]

hello all, 

I checked the ups and found that R38 and R43 connected with the drain of 2N7000 mosfet got burnt and replaced burnt resistor and F3.Then the Ups energized and started working 

but still the Resistances 38 and 43 (1K 1/4 watts ) are getting hot. What may be the possible reason.Please check the attachment and refer sheet number 3 for detailed circuit 

Resistors R38 and R43 are getting hot  only during standby/charging operation and resistors are normal during ups backup on condition. 

Thanks   

[Brad_C]

That's "normal" behaviour for the old 3rd generation 48V units. Replace them with 1W resistors and stand them off the board. I found a resistor at RadioSpares (RS) with small enough leads that fit through the holes in the board but it was a bit of a search.

if you are replacing parts, replace bootstrap caps C34 & C35 while you are in there. They get exposed to quite some heat and tend to dry out. They're not critical, but I've never found any that are close to spec after 10 years.

[Anonymous user]

Thanks Brad for the quick response.i found the F3 fused and used a thin wire to test and the unit is functional. Only during charging the resistors 1K are heating up.

I don’t know which generation is the ups .The model number is YS 0139121473 and as per the model number the product is manufactured on 2001 39th week 

[Brad_C · Accepted solution]

Yes, the 3.x & 4th gen units (late black faced SU and all SUA and above) don't have this issue as they use a dedicated high side driver for the MOSFET bridge rather than the discrete bootstrap driver which has this flaw.

When I bought my first 2200 the resistors had gone, taken out both high side drivers which then turned on both sides of the bridge simultaneously and destroyed half the MOSFETS. Oddly enough it didn't damage the fuse, just most of the driver transistors and the MOSFETS.

It did sound impressive when it went bang though and let a lot of magic smoke out. Put higher power rated resistors in, give them room to breathe and keep them away from the other components and it'll probably be ok.

I did a battery calibration on a 2200 last week, and after 2 hours (it has an extra 55ah of external battery) at a 1KW resistive load I realised the fan had died, the internal temp was >65C and it smelt a bit funny. A new fan and a bit of a once over and it's good as gold. These units are very well designed and solidly built.