Sorry for the long first post, but a strange problem has recently developed with my mid 80's vintage Syncrowave 300 welder.

In low current range the welder behaves perfectly fine, AC works well, HF works, pulser works, current output is linear and smooth. When I switch it to the High range it is basically wide open. It outputs close to 300 amps I would estimate (vaporizes 3/32" tungsten) and there is no throttle control either using the foot pedal or the panel control.

So I took some readings from the output of the hall effect sensor, Pin 87, and found the output voltage is approximately correct in the low range, but is wide open in the high range. OCV is also right at 79.5 volts and seems about right while welding.

Here are some average values - in low should be -1 volt per 20 amps and in high -1 volt for 100 amps

20 amp dial = -1.2v
40 amp dial = -2.3v
60 amp dial = -3.5v
75 amp dial = -4.3v

100 amp dial = -4.4v
250 amp dial = -4.5v

So to me this proves the LEM is working properly and the problem is exclussive to the high range. I checked out the schematics and it looks like the only difference is the low range reactor and turns through the LEM core.

Has anyone seen anything like this before or have any theories on what could be going on?