dave wrote:

- if the footpedal functions seem workable, and

Does it have an amp meter? If so, just short the electrode to the
ground clamp, and press the pedal. If the current follows the pedal,
the current regulator works.
- if the gas and water flow solenoids (and their related circuits and
hoses and such) seem workable, and

Listen for the click, it should be plainly audible. My Lincoln only has
a gas solenoid. There is a pre-flow timer that prevents the HF from
turning on until the delay times out. So, when you press the pedal,
there should be a clunk, then after a bit the HF should start hissing,
then after you let up on the pedal, after a delay, the gas solenoid
should clunk again.
- if the HF spark-gap point setup is functioning, and

Just set up to weld with no gas. If the HF is working, you should get
little lightning bolts 1/4" or so through air. (They will be a LOT
longer with Argon.)

- if the TIG gas regulator and flowmeter seems workable


Harder to test without some compressed gas with the right thread on the
bottle.

Jon