Tripp Lite SUINT1000XL

[Thedon]

Hello all,
Thought I would share my experience repairing a Tripp Lite SUINT1000XL
https://www.tripplite.com/smartonline-230v-1kva-700w-double-conversion-ups-tower-c14-inlet-db9-serial~SUINT1000XL/

I’ll mention that repairing UPSs has been hit and miss for me more miss as most UPS have an assortment of exotic FETs, diode packs and sometimes IGBTs. Luckily this UPS has readily available MOSFETs and diode packs which I sourced from E14 costing me around $56.
Brief history I sourced this UPS from work which just failed displaying a red light showing fail on the front panel and not allowing the computer and all the peripherals connected to it to power up, the unit has four AC outputs and one input at the back of the unit. One of the techs decided to take the cover off and have look inside and check all fuses. He found the two 20A fuses on the main board blown so he replaced them not before disconnecting one of the battery inputs upon replacing the fuses and reconnecting the battery the battery terminal arced/exploded and blew the fuses again. After he changed his underpants the powers that be decided to throw it out.
I decided to have a look and see if I could resurrect the device, after visual checks I checked all semiconductor devices screwed to the two heatsinks. I found the following components destroyed which were screwed to the main heatsink;
X2 MUR860 Ultra-fast diodes 8A 600V
X1 SPP20N60C3 650V MOSFET N-CH
X1 IRF3710PBF 100V 57A MOSFET N-CH
X2 2SK3878 (F) 900V 9A MOSFET N-CH
X1 T10XB60 Bridge Rectifier
 
Tracing the circuit board from the battery terminals it seems the destroyed components forms the battery charging and inverter circuit, components on the small heatsink at the bottom of the PCB form probably a final inverter circuit as the AC outputs are to the right and below the heatsink. I’m not sure which component was the culprit for destroying all the other components I suspect it was SC7 one of the 2SK3878 MOSFETs as you can see in the photo there is a smoke vent in the body. I got to say I don’t have much confidence in this design, one component fails which causes a cascading effect but what do I know.
I went about replacing all the components installed on the main heatsink as the total price wasn’t to extreme considering the unit sells for $850US. When I removed the heatsink I found black soot on the heat sink and one of the main filter caps which was caused by a 125V/7A fuse there wasn’t much left it was obliterated the photo shows what was left after cleaning you can see only the legs remain. I replaced it with a 7A pico-fuse.
I tried to get the battery wire off the top battery but it wouldn’t budge completely fused so I measured the voltage which was approx. 12.3V and supplied it to a load consisting of a LED lamp it illuminated the lamp no problems and at the same time measuring voltage which dropped  very slowly. I would have preferred to use an electronic load but don’t have one so decided the battery was ok. After reinstalling the main board, cleaning all soot and reconnecting all wiring I powered the device up without connecting it to mains. The display lit up informing me that it was running on battery power with an annoying beeping coming from a piezo buzzer I didn’t know was there, no load was connected I then connected it to mains and you could hear relays clicking and the display indicated that it switched over from battery to mains power. Before connecting any loads I measured the battery voltage at the terminals and it measured approx. 39V so batteries must be in series I then measured temperatures with a IR thermometer after a couple of hours nothing stood out I again measured battery voltage which was 40V. Next I connected my computer and monitor and after powering up the unit’s fan ramped up in rpm and the display indicated a 25% load after the computer finished booting up and everything stabilised the display didn’t indicate any load. It’s been running now for a couple of days and I have been testing it by disconnecting the mains it transfers to battery power without the computer resetting or display flickering transition is flawless so that probably means the inverter is constantly fed with battery power. I have had the computer/monitor running for over an hour and the unit doesn’t indicate the batteries are draining probably could run for hours must try it when I have time.
All up it is quite a good unit performance wise but like I said before not confident in the design.