schematics help

[Richard.]

Fingers crossed. At least you can still use it I guess.

 

[wheresmejumper]

Yeah it still welds better than the later selco manufactured Invertecs that replaced it

 

[wheresmejumper]

Fuse on the following board blew.i replaced it with a slightly higher fuse but a component right before the fuse heated up and blew fuse again.its name is ntc1 which googling says is probably a negative temperature coefficient thermistor. How do i find out what value i need to get?

 

[Jim Davey]

Check the bridge rectifier isn't dead short. I've had loads of those PCBs die on me in various Lincoln/Selco inverters.

 

[wheresmejumper]

Ill check that.cheap repair if so

 

[Jim Davey]

Those primary power boards were a nightmare. If customers lost a phase or powered the set up on a single phase 400 volt circuit that PCB always got fried.
I binned about 6 of them last year (dead ones that I kept for spares) as ive got rid of all but one or two machines with those boards now.

 

[wheresmejumper]

I couldve done with some spares Jim!theres a couple on ebay but too much for a spares machine.

 

[wheresmejumper]

The rectifier checks out.signs of overheating at 4 resistors so new ones ordered along with 2 thermistors.guesswork to size them so stab in the dark

 

[wheresmejumper]

Replaced 4 resistors and the thermistor before the glass fuse.
It idles grand,but even striking an arc alone and stopping,leads to the 2 black resistors overheating and melting the glue that holds them.and stuff in the vacinity

ill have to remove the board again and investigate.
what would resistors that physically big be there to do?

 

[Richard.]

I'm working with a guy that repairs welding machines day in day out this week. Give me a list of your questions you need answers too and I'm sure he'll be able to help. There is not much he doesn't know about the guts of these things.

 

[wheresmejumper]

Cheers Richard
i suppose the main thing is where along the line would you expect voltage to disappear,seeing as caps and diodes check out.ill have to check the transformer in case thats not putting out what it should

 

[Richard.]

I'll ask the question tomorrow and no doubt the guy will have some suggestions for you.