Repaired power supply but some little smoke comes out

[SM-Piyes90]

Hello everyone .

I have recently being repairing a high current power supply belonging to a MMA welder .

I have found a part that was totally burned near a 300 : 24 v ( 150:5) transformer .

Now after recovering that section with new components , i see a little smoke coming out near the 300 V connector while the unit is on , that connector is surrounded by two big 4.7 uF (red )caps in parallel and 2 blue HV PTC or NTC varistors .

Any ideas ? can those varistors be weak and make that section burn again ?


here is a picture :

[momaka]

Re: Repaired power supply but some little smoke comes out

Kind of a late reply...

but yes, "weak" or "blown" NTCs on the input can smoke or heat up excessively.

Some better pictures with the board out of the case may be helpful here. Hard to see what exactly is connected to what.

Is there a triac controlling the input to the transformer, by the way?