Hi.

I'm repairing a 1000W inverter (SMPS). All 12 low voltage MOSFETs IRF540 were bad and I replaced them. Two of eight high voltage MOSFETs IRF740 were bad and I replaced them. I found a bad 1N4007 diode and replaced it.
Now there are four TO-220AC isolated diodes (two legs) mounted to a heatsink. These are fast rectifier high voltage diodes used with the two big high voltage capacitors. One of these diodes is bad. The part number of these diodes is erased... The output voltage of the inverter is 220V, and the capacitors are 350V.

In a 600W inverter I have, diodes SUF30J (600V, 3A, 35ns) were used for high voltage rectification. So I think a 600V 8A and minimum trr should work...
so I think MURF860 would be ok. It's not available isolated here so I may use an isolation. Also there are BY329F and BYV29.
I think it's better to replace all four diodes. I found in an old tv board a FMG-G26 (600V, 4A, 100ns, isolated ). I'll try the Inverter after a while with it and get back to see your recommendation.

Another thing, I found a diode in the inverter thats gives me 185 when testing with the DMM, in the forward direction. I tested it out from the circuit board. It is SR106. Is this a bad diode or it's like that..? It is in series with a 5.6KΩ 1/4W resistor and the resistor isn't bad.

Regards,
Hazim

 

hazim,
Do you know what caused the failure? I hate to see you go through all the trouble of replacing the parts just to watch it go boom again!

Sorrt, can't help with the diode issues...

 

I know that I should know the reason of the failure, but I don't know it and can't know it simply because someone got it bad and gave it for me to repair. Usually inverters are damaged because of overload even if they have overload protection (according to the brand and design...) and also because of the bad electricity service here in Lebanon (it's actually a UPS and not only inverter), here the mains voltage is 220V AC, but due to the bad services it comes sometimes less than 100V. This makes almost each house hase an AVR and sometimes two AVRs connected in series. Also the electricity sometimes goes ON and OFF many times very fast and damage electric appliances...

 

I know that I should know the reason of the failure, but I don't know it and can't know it simply because someone got it bad and gave it for me to repair. Usually inverters are damaged because of overload even if they have overload protection (according to the brand and design...) and also because of the bad electricity service here in Lebanon (it's actually a UPS and not only inverter), here the mains voltage is 220V AC, but due to the bad services it comes sometimes less than 100V. This makes almost each house hase an AVR and sometimes two AVRs connected in series. Also the electricity sometimes goes ON and OFF many times very fast and damage electric appliances...

Sounds like a good explanation to me. Then it's worth repairing. I hope someone can help you out. Let us know on your progress.