Welder not turning on - Learning

[Olles4]

Is it better to put higher or lower value resistor on R209 and R207 ? I mean which way is safer.

[CapLeaker]

That's the problem. Them 2 resistors I am not so sure of what there was in there, I went after the carnage trying to identify what was there first place. Some were really easy to identify, others not so. The thing here is to go through example circuits that are similar to yours and see what they used. Pull up some datasheets from the PWM from different manufacturers and compare. Sometime you know the resistor code started with a 1 and ended in a zero for example. So far R207 and R209 I haven't come up with anything too good uet.

R207 ended with xx01. So a 1001 = 1k ohm. Sounds plausible and should work.
R209 got not a clue. Cording to your schematic, it is a gate drive resistor to a different MOSFET. Knowing that it should be something less than 100 Ohm. Don't forget there are already 22Ohms in line.

[CapLeaker]

Oyyy, made a mistake yesterday, R209 goes to the Source, not to the gate. It's a current sense resistor. So 1 v is the max here. As soon as the CS pin goes above 1V there is current limiting / cut off. Thinking about this, the resistance must be quite high. Higher than 1k Ohms. More like something 10k or 100k Ohms. Can you check the capacitance of C204?

[Olles4]

Oyyy, made a mistake yesterday, R209 goes to the Source, not to the gate. It's a current sense resistor. So 1 v is the max here. As soon as the CS pin goes above 1V there is current limiting / cut off. Thinking about this, the resistance must be quite high. Higher than 1k Ohms. More like something 10k or 100k Ohms. Can you check the capacitance of C204?

Update:

Here is some photos of the main board. Im trying to remove the big heatsinks right now to see what is under them.

[Olles4]

Heatsinks and fans out here are some more photos.

[CapLeaker]

What a pain that is! Looks like it has some bad solder joints too.

[Olles4]

What a pain that is! Looks like it has some bad solder joints too.

Which one?

[sam_sam_sam]

What a pain that is! Looks like it has some bad solder joints too.

Some soldering joints do not look so good especially the lager pin components if it were me doing this I would re-solder those joints for good measure

[CapLeaker]

The biggest problem with an inverter welder is not continuity like voltage, it's more current based like. The circuit has to be able to carry the current. I do remember a case not too long ago, where one of the problems was burnt track on the PCB that made continuity but couldn't carry any load.

So what was your “incident”? I don't see anything blown up (yet)?

[Olles4]

The biggest problem with an inverter welder is not continuity like voltage, it's more current based like. The circuit has to be able to carry the current. I do remember a case not too long ago, where one of the problems was burnt track on the PCB that made continuity but couldn't carry any load.

So what was your “incident”? I don't see anything blown up (yet)?

Nothing blown up just one of the heatsink was under voltage so it shocked me.. but it's connected to diode which's base is connected to the line.

I understand that but the problem is it didn't even turns on.

[CapLeaker]

Show me what heatsink and what diode. The welder may not turn on if the low voltage supply isn't working.

[Olles4]

Show me what heatsink and what diode. The welder may not turn on if the low voltage supply isn't working.

Heatsink connected to this row of components.
4x STTH12R06D
2x 1H18AF

[Olles4]

So this is the front lcd panel with potentiometers and welding style adjustments with a small pcb it's connected with 2 cables to the main board

[Olles4]

These are the 2 connectors. So I assume the small board next to it what we were fixing it's part of the supply.

[CapLeaker]

Heatsink connected to this row of components.
4x STTH12R06D
2x 1H18AF

The 2 IGBT's are FGH60N60's. If they are blown, there is plenty to be had.

[CapLeaker]

So this is the front lcd panel with potentiometers and welding style adjustments with a small pcb it's connected with 2 cables to the main board

I was pretty sure that front LCD panel works of that board, but I guess not. Or does it loop just through that main board, but the power comes from the little board?

[Olles4]

These two are bridge rectifier's am I right ?

[CapLeaker]

yes

[Olles4]

yes

Hello. I have done some measurings. So on the small board the IC UC3843 pin6 (output to gate) is only 0,7mV and it seems like it didn't want to drive the mosfet
How much Volts should i get on mosfet Drain and Source ?
here is a link to ic UC3843BN datasheet(1/15 Pages) STMICROELECTRONICS | HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER (alldatasheet.com)

[Olles4]

Oyyy, made a mistake yesterday, R209 goes to the Source, not to the gate. It's a current sense resistor. So 1 v is the max here. As soon as the CS pin goes above 1V there is current limiting / cut off. Thinking about this, the resistance must be quite high. Higher than 1k Ohms. More like something 10k or 100k Ohms. Can you check the capacitance of C204?

c209 is jumpy but its something around 17 nanoF