Lincoln Wirematic 250 problem

Hi John...well, when you think about it, it really is a power supply.

John, that's a fantastic idea. Problem is with resistors... I might be able to scrounge a few here and there but I'm not sure how high I'll be able to bring the amperage without smoking them. I do have a 50 ohm/200 W load resistor for ham radio applications and that should give me a few amps of load there. But then again, I would probably want to go the other route (ie. brick and a wire) as I really don't want to blow my dummy load. :)

But nevertheless, excellent idea there John. Thank you!

Alex

Hi Mylo... yes, that's the manual I was talking about. You got the wiring diag but no control board. I think that's a non repairable item but I might be wrong. This thing is covered with a thick layer of conformal coating. I did check the thermostats but I'll check them again....short them out if I have just to make sure all is ok.

thanks! Alex

Gary, one more thing...

The control board has quite a few feedback inputs. I was able to trace a current sensing input as well as the output voltage one. There might, or might not be a phase detector input as well which would allow the micro to sync itself with the incoming AC phase and thus fire the SCRs at a proper time. I was kinda guessing that perhaps one of those inputs got messed up, which would make the micro go awry and screw up the firing sequence. Now that a few days have passed I question myself whether the transition from good to bad and back to good weld was uniform and predictable or random.

Alex

How about high intensity lamps for active/passive loads.

Not so much the screw in type, but they work - filament type not gas type...

I was thinking SUN GUN or long strip glass tube with coil lamps. Parking lots have them ..... Lighting store. - Electriction might have some junk/second hand holders - buy a couple of lamps - 1kw lamp goes a long way.

Martin

My feeling is that such a desynchronization would very quickly result in the SCRs being blown. In other words, the odds favor both legs being active at the same time, which would present essentially a dead short to the transformer secondary.

Gary

OK guys... the Wirematic saga continues. I haven't had time to look at the machine for a few days and this might have helped things.... Today, I either had a brainstorm or a brainfart... and remembered something that now I think I should have investigated further when I took the SCRs out for testing.

When I removed the SCRs for bench testing, I've noticed that the surface of both SCRs as well as the surface of the heatsink where the SCRs make contact with, have either signs of pitting or corossion. Where there was a bump in the heatsink, the corresponding point on the surface of the SCR would have a dip. At first, I didn't even think that this is pitting or corossion. My initial thought was that this allows the SCR to sit tightly against the surface of the heatsink and/or allows precise repositioning of the SCR in case it is ever removed, etc. Now, don't laugh as I have NEVER worked on high current equipment and I really don't know what to expect when examining such problems.

Now that I'm thinking about it, it doesn't make any sense to me. You'd expect to have a clean point of contact between the SCR and the heatsink to allow the maximum transfer of current from the SCR to the heatsink (and consequently to the gun). The uneven surface that I'm seeing there is probably a result of moisture getting in there and corroding the surface of both, or a sign on sparking. It may not be as critical in low current equipment but I'd think that it would make a heck of a difference in instances where a very high current is needed at a steady voltage.

Can you guys confirm this for me? I am planning to go back to my friend's either tomorrow or the day after.

Your thoughts would be muchly appreciated.

Alex

replying to Alex Wiecek, Nathan414 wrote: Change the liner