Weldteam 170i, help repair

[malonph]

A friend gave me a broken weldteam 170i (air liquide).

It had a blown capacitor and a burnt IGBT, I managed to fix that and now the machine seems to start correctly to green light (it was stuck at yellow light).

When I try to weld something it does starts arc but is really weak and the power resistor shown in the photo below gets red hot.

Can you please help me with this?

Thank you very much

 

[Wendelspanswick]

Well if no one else is going to chip in, have you checked the rectifying diodes?

 

[skotl]

@Jim Davey is the man to ask, I'd think!

And defo check the diodes.

 

[Jim Davey]

I'd be following the circuit and seeing what components are downstream of that resistor.

 

[eSCHEn]

Any reason why that relay has a nasty big hole in it?

 

[500e]

Fair bit of corrosion on board as well, the hole looks as if the contacts got Hot?

 

[malonph]

The hole in the relay looks manmade, it has no signs of overheating and I tested it. As suggested I'm going to follow the circuit and check every component that's attached to the resistor.

 

[Jim Davey]

Whatever is dragging current through the resistor is going through those relay contacts.
It's the charging circuit for the primary side of the inverter, it should charge up the caps through the resistor.

 

[R Kraft]

If I was to guess.
The resistor that gets hot is a precharge resistor, that keeps the capacitors charged and ready to go when the welder is idle.
When you try to weld the relay would kick in and bypass the resistor and supply full power to the power capacitors.
Does the relay try to function when you try to weld ?

 

[malonph]

I double-checked the relay just to find that it had a plastic chip inside causing it to fail randomly. I've changed it and now the machine works like a charm. I can say this is solved.

Thank you gentlemen for your support.

 

[eSCHEn]

Fantastic Well done for fixing it.

 

[R Kraft]

Your very welcome.

 

[skotl]

Good work