Hitachi gp2 , faulty

[Swillytucker]

Hi , I'm new on here, but browse posts now and again for useful info.
I have an old Hitachi gp2 300a Tig which I really loved the last few years I've had it, unfortunately it's started faulting to 100a whatever it's set on. It works when cold for few seconds then faults, it also works ok for MMA.
I seen some old posts on here about these sets and I wondered if anyone had any info on them? Manual, circuit diagram or even an old machine with possible parts, PCB etc to buy. Or anyone had this fault before, I've tested the pots and wiring from remote to machine and seems ok, looks to be internal.
Any help would be really appreciated, I can't bear to be buying a new digital machine when this probably just needs some small cheap fix if I just knew what.
Thanks

 

[Popcorn]

Seem to remember @Hitch had a Hitachi

 

[badabec]

Can you post some clear, in focus, close up photos of the circuit boards?
I know nothing but it may help the diagnosis.

 

[Nick DV]

Hi & welcome

 

[Swillytucker]

Hi thanks, here's the circuit boards on top. The 2 red and 2 black wires coming in on top left are from the potentiometers and recon I tested them here as ok. I'm not that electronically savvy but can do basics and have friends who are but not necessarily welders

.

 

[hotponyshoes]

Maybe I'm being thick but I can't even see a pot on the front panel for the main current?
Is that adjusted remotely?

If it is remote then try unplugging the remote (or the panel Pot if I've missed it)
With the pot unplugged I'd expect the machine to either run constantly at full power or constantly at zero/minimum power (or show a fault if it has that capability?)

That should at least tell you if you should be looking at the machine or the pot.

 

[hotponyshoes]

Also, maybe put a meter on the contacts of thr process selection switch and make sure it is actually selecting the base process correctly.

 

[addjunkie]

Wasnt @HughF a hitachi man?

 

[Swillytucker]

Hi

Maybe I'm being thick but I can't even see a pot on the front panel for the main current?
Is that adjusted remotely?

If it is remote then try unplugging the remote (or the panel Pot if I've missed it)
With the pot unplugged I'd expect the machine to either run constantly at full power or constantly at zero/minimum power (or show a fault if it has that capability?)

That should at least tell you if you should be looking at the machine or the pot.

Hi so yes it does have remote pot, , I've tried with unplugged remote and when the machine isn't at fault it welds on lowest setting. If the machine has been used a bit and fault has started then unplugged remote it's at 100A! not sure what that tells me, (not the pot?)
I also had a look at mode settings dial switch and it's part of little PCB with other 2 dials on front and 3 ribbon wires attached going to main pcb, not that easy to test. but dial is rotating little copper arm, I blew out and sprayed little contact cleaner , rotated back and forth. then machine worked ok for longer than it has?!? But did fault eventually . I'll need to investigate this switch better later when I'm not meant to be doing actual work. It's definitely something that warms up with a little use then faults to 100a. So could well be small copper contacts in switch.
Thanks for the help

 

[hotponyshoes]

Hi

Hi so yes it does have remote pot, , I've tried with unplugged remote and when the machine isn't at fault it welds on lowest setting. If the machine has been used a bit and fault has started then unplugged remote it's at 100A! not sure what that tells me, (not the pot?)
I also had a look at mode settings dial switch and it's part of little PCB with other 2 dials on front and 3 ribbon wires attached going to main pcb, not that easy to test. but dial is rotating little copper arm, I blew out and sprayed little contact cleaner , rotated back and forth. then machine worked ok for longer than it has?!? But did fault eventually . I'll need to investigate this switch better later when I'm not meant to be doing actual work. It's definitely something that warms up with a little use then faults to 100a. So could well be small copper contacts in switch.
Thanks for the help

That's suggesting to me that it's switching itself into one of the other tig modes and (when it's outputting 100a) it's running in crater fill or something.

There are 4 pots in a line on the top left of the panel.
Turn the left 3 all the way up (or down) and see if the 100a level changes when it faults