As it works for a short while then fails I would guess something is getting warm and failing. At least there is nothing exotic on the board, you should be able to test most of it with the diode setting on a multi meter. Have a look on You tube for transistor and diode testing with a multi meter.
Remember to keep us updated with your progress as and when you get time to work on it, nothing worse than looking at a unresolved thread and wondering if the problem was ever solved.I agree, it just ****** me off because it worked fine in England last month, must have got travel sick.
I have no problem testing pcb's, only problem here in Estonia is sourcing components off the shelf.
Cheers
Bob
Bob was last on Aug 2017 but failed to update.........I know this is an old(ish) thread, but did you ever get the Clarke 165 working? Just interested, as I used to have one of those (until just a few months ago). I bought it new in 1982 or thereabouts, and it never missed a beat 'til the day I sold it. It must have been one of the earliest models, as MachineMart supplied it with a full size CO2 bottle with a dip tube! - they knew very little about mig in those days.
I only sold it to buy an inverter for portability reasons. By the way, there was a lead with a din connector coming from the torch lead, to plug in to the din socket next to the wire speed knob. Maybe that has a bearing on the wire speed issue.