I have a syncro 250 (Model JK54xxxxx)that I have never actually gotten the pedal to work on. Tonight I finally spent some time with the cover off, and a meter. I have a pdf of a service manual, but it does not have my wiring diagram in it, though it does have the schematic, and a section on measuring voltages and wave forms. I did not bother getting the scope off the shelf to look at ave forms because the machine works perfect in stick mode, and it semi-works in tig mode if I leave amperage control at panel and just use the pedal as an on off control ( with contactor set to remote)

Measuring the pedal while disconnected from machine it looks like it is fine, 0-1k varying resistance, and A-B is on off as it should be.
I measured every voltage from RC55 and RC54 on the main board. The guide( TM353 in footnote, t353e.pdf filename) has the pins numbered, not lettered. My board seems to have letters, but the sequence seems to match up for expected values, except for 2 things:
RC55 pin 4 always reads 0v, but should be 0-4v as arc force is adjusted with the switch on. RC55 pin 10 does vary from 0-4 with the switch off.
and the really relevant thing:

RC54 pin 9 - should be 0-10v varying with amperage adjustment with contactor on. RC54 8 reas fine from 0-10 as amperage is adjusted with machine knob.
RC54 pin 9 does not vary, and reads -5.8v with the pedal connected.
When I disconnect the pedal it reads -10v.
That pin 9 wire is labeled 106 in my machine, which I traced to pin C on pedal connector RC1. ( should be 0-10v signal in from the board?) Measuring on the back of RC1 I can measure from E to D and the value goes from 0v to -5.8v as I fully depress the pedal.

It seems like my root problem is that I am getting -5.8v from the main board instead of +10v. Any one ever dig this deep into a machine to figure out why, and if it can be fixed?