welder problem

[asgard]

Well, after a couple of years of good service from my Harbor Freight 170 amp welder it decided to play up. I had just finished welding some 3/8 inch angle to a heaver section of plate and all was well. I then started to tack weld some grate sections and the power went down. It is still welding but is now low on power.
I have taken it apart and it is an AC to DC unit, the bridge regulator seems to be OK, I check all the diodes - although they were still connected to the inputs and they all showed at .54 which is within spec, they show open when reversed. The unit has 20 volts DC on the output. It has 8 diodes and I have read that this is the most likely issue.
Am I missing something in the testing, should the diodes be disconnected from each other and the drop in power only related to diode issues?
I have been looking at these single bridge diodes 200 amp, think that is overkill but no marking exist on the diodes I can see, it would appear that the 180 amp version has 16 diodes and the 170 amp 8, I believe that affects the duty cycle. What are your thoughts?
It says single phase bridge regulator.
Anything you can suggest would be greatly appreciated.

 

[85Hokie]

anything in the cable(s) that could affect this power drop?

 

[asgard]

The cables both internally between components test OK. The external cables from ground to clamp and terminal to torch also seem OK. I have only visually inspected for cuts and loose terminals and carried out a continuity test.
The welder works but just low on output, max stage 2 is what used to be max stage 1 if that makes any sense.

 

[m32825]

If you're testing multiple diodes in parallel you have to lift one of the legs to isolate each one.

-- Carl

 

[Yooper]

Your situation sounds like a common issue of a loose wire at either the breaker or the outlet. Because welders draw a good amount of amps, heat cycling occurs in the wiring connections and they tend to loosen up after a while. Have you tried welding again with it cooled off? If it welds OK when cool and gets worse as you go, this is probably your problem. Solid wire is notorious for this. Let us know what you find! Good luck!