115VAC to 28VDC Converter Fried Resistor

[tccotham]

I'm troubleshooting a 115vac to 28vdc converter card that burned up a big 19 ohm, 5watt resistor that was connected to the rectifier output (removed but previously installed on right side of first picture). I previously fixed one of these that has a shorted MOSFET burning up the same resistor. On this one I can't seem to find any shorts, rectifier tests good, MOSFETs check good. Is there any other component or condition that would likely cause this in a AC/DC conversion circuit?

 

[Delta Prime]

I'm troubleshooting a 115vac to 28vdc converter card that burned up a big 19 ohm

Make model converter card please

 

[kellys_eye]

Can we see a close up of this part of the board?

The big resistor that burned could well have been a current limiter in case of shorts but the MOSFET and resistor would have been part of the input switching circuit that also includes the primary of the SMPS inductor as well as the flyback diode, either of which might have gone open circuit..

 

[tccotham]

It's a Milpower M1982-23 converter for aviation use. I'll try to get your a better picture of that area but I can't remove the board from the case without a lot more maintenance. I know those two smaller mosfets on the left side are SPP11N653C.

 

[kellys_eye]

It's a Milpower M1982-23 converter for aviation use.

If it's still being used in flight then I'll bow out of this thread. Such equipment needs to be sorted professionally or replaced for safety reasons.

 

[Delta Prime]

It's a Milpower M1982-23 converter for aviation use

Being an principal investigator for aerospace non-combatant military contractor 2 years. I must ask.
Is this an RMA ?
(Return Merchandise Authorization)
You're the one who's going to have to sign off on the repair and or calibration.
Would you happen to have a schematic?