Had this welder for some time and it worked perfectly, SMAW and GTAW at all amperages. Now it immediately goes to max amperage for each of the three ranges (H, M, L), whenever a load is appled. When I pull out the PC board it goes to minimum amperage. Board has been checked on another identical machine and works well.
Is the foot pedal cable crushed and shorting or open ? No pcb - cable disconnect. PCB - cable do something. Maybe it is a switch or like item - a Amp POT (e.g. like a volume control on current ) Maybe the wiper is dirty.
What was disconnected when the board was taken out ?
Current transformer leads attached inside ?....
Taking the board out seems like it goes into a protective / safety poise.
The potentiometers in the foot pedal and on the panel test OK; however, I've tried both to control the ampacity and they are ineffective.
The PC board plugs into a 15 point connector mounted on the back of the front panel. It was the only thing taken out when I tested electrode ouputs (i.e., when in, the electrode goes max, when out it goes min).
I'll double check all the resistors and the main transformer leads.
I have briefly checked the web for additional information about your machine but have found nothing, so I'll make some general suggestions that may be helpful. If you know of a wiring diagram online that I could examine, I'll try to be of more help.
I would check the control circutry components like potentiometer wiring and the remote/local switch.
If your machine uses feedback from a shunt or current sensor to regulate the output, check that a feedback signal is getting to the control board. (I suspect that your machine is too old for this type of control, but I'm not certain.)
The fact that you can get full output, and that output dropps to min when the board is disconnected, indicates to me that the main transformer, saturable reactor, and control power supply are probably working.
Both of the pots for varying amperage (panel and foot control) check out ok. The remote local switch does as well.
The Chemetron P&H was made back in 1982. P&H sold the proprietary stuff to Chemetron which ceased making them years ago. I know there is a wiring schematic out there somewhere but so far I've not found it.