XMT 304 Board Issues

[pdexter1210]

Yes it is.

[pdexter1210]

Ok, so this evening I swapped the small board off of my working machine onto the one I'm working on at the moment. With the little board from the working machine installed I get the correct pre-power readings. So I powered the machine up using each of the three PC1 boards I have from the nonworking units. Here is what I get, first PC1 board = Help 7, second PC1 board reads Help 6, third PC1 board reads normal voltage, but fractional amps.

When I swapped in the PC1 board from my working machine, this machine powers up just fine. I think this means I have 3 failed small boards, although R7 on each of them reads 200 ohms as it should, so something else on these little boards must be broken. Any ideas on how to diagnose the small boards?

Next, it seems that 3 of my PC1 boards are in need of repairs. Any thoughts on where to start with each of them, given their help codes and the knowledge that the machine works fine with a good board swapped in?

[pdexter1210]

Here are some close ups of one of the bad pc boards. The resistor R7 measures 200 ohms as it should, but I'm not sure what else to check. When installed this board causes a working machine to fail the pre-power check, reading 3+Mohms from SCR - to the positive terminal. I've tried looking up the part by the part number listed, but can't seem to find anything for sale. Appreciate any guidance on what else to diagnose on this board and/or a parts supplier for this part. Thanks.

[Bushytails]

I don't see anything wrong with that board... I wonder if there's version mismatches or something, or the problem is on the other end of the molex plug...

[pdexter1210]

That's an interesting point about it being the wrong board. The part number on this board is 197039, but the parts manual calls for 198095, it appears to be an exact replica so I didn't think much about it, but maybe it's just the wrong board? I guess I'll give Miller a call and see what they tell me.

[pdexter1210]

Ugh, called Miller and the small board isn't sold separately, have to buy it with the big board. They didn't have any test procedures to walk through to diagnose the problem.

[Bushytails]

Is the molex connector you're plugging into it burnt, or the board it goes to bad?

[pdexter1210]

Nope, plug is good. And machine works fine with good board in replacement of bad board.

[jjohn76]

If the contact terminals are all shown proper resistance, does anything look wrong with the two capacitors? I can't see anything wrong on those small boards.

[Bushytails]

Their problem is somehow the 200 ohm resistor is good, but isn't measured at the SCR terminals on 3 of the 4 board, put into the same machine with RC1 going to the same place... which I do not understand.

[pdexter1210]

Just wanted to follow up here to close this out. I sent the two main boards and the two small boards out for repairs. Reinstalled them when the repairs were complete and the welders are working fine. Bit frustrating because I still don't know what was actually wrong with them, but alas, working is better than broken.

[jjohn76]

Great news!

[blue_tech]

Are you powering this on 230v or 460v when you get the Help Codes? Some of the help codes you are describing occur when the bus caps don't charge up to the same amount. When the unit is on 230v, the bus caps are in parallel and the voltage will always be the same, but when you power the unit on 460v, the caps are in series and if there is an issue with the caps, you get a voltage differential on the caps and a Help Code.