Help needed millermatic 175 trouble

[adamstracy26]

I have a millermatic 175 that died. Ser#LE263696 Board#207466. The welder will feed for less than a second then just stops. Incoming voltage has already been verified at the control board and the cooling fan runs fine and I have no overload light on. The trigger relay and gas relay pick up when the trigger is pressed.

This is how far I have gotten:
when the trigger is pressed, I get about 30vac going to the main transformer (measured at RC6 & RC7 on the control board)then it almost instantly bleeds down to zero. When this happens I also get a 12dc to the drive motor for less than a second then it also bleeds off to zero. I'm just not getting any power from the board to the transformer or drive motor for more than a split second.

any help would be greatly appreciated

[labmaster02]

Help needed millermatic 175 trouble

Have you tried removing the wire and then removing the gun, leave the pigtail for the switch plugged in? Turn it on and pull the trigger. This will eliminate any shorts in the gun or wire to case. Just a thought.

[adamstracy26]

Sure did, I actually removed the gun totally and jumped the trigger switch remotely.

[ryanjones2150]

Help needed millermatic 175 trouble

I had a lincoln mig that did that exact thing, can't remember the model, it's been a couple welders ago. I sat it under my work bench for a while until I had a chance to work on it, by that time I had a new machine. When I pulled it out, I cleaned the machine front to back including reseating every plug I could. When I was done, the machine welded just fine, gave it to a buddy of mine that needed one.

[adamstracy26]

Already did that also.. Sad part is this machine has little use and was always kept in a climate controlled environment. It's extremely clean and all connections are like new no oxidation at all.

[Meltedmetal]

Maybe check TP1 for correct operation.---Meltedmetal

[adamstracy26]

Definetly have continuity through TP1 and if I unplug the overload I get my over temp light like I'm supposed to.

[Meltedmetal]

It sounds like something is heating up very quickly and shutting down. If you are comfortable with it,you could try hooking a volt meter across TP1 and turn on the power. It should read 0v. pull the trigger and it should still read 0v. If you get a voltage reading when it shuts down it is at least partially opening. I suppose you could try some freeze spray to see where and if it comes back to life maybe. Good luck.

[adamstracy26]

TP1 stays 0 volts and everything stays very cool to the touch. This thing is kicking my butt..I also disconnected the primary side of the main transformer and with it disconnected I get 240vac on terminals RC6&RC7 when the trigger is pressed. I have checked the transformer and it is not shorted to ground, and I have continuity between the primary windings. I also checked the secondary windings and I have continuity there also with no short to ground nor is there continuity between primary and secondary windings.

[Meltedmetal]

Do you still have 230v at RC10 & RC5 when the feed stops? Might try voltage drop test across CB1 and each individual line of S1(power switch) when the feed stops. I don't see much else outside the board that would cause this issue.

[adamstracy26]

Yes already verified CB1 and S1 was verified at the board terminals RC3-1 to ground =120vac and RC3-8 to ground = 120vac. As well as RC3-1 to RC3-8 =230vac... I also feel all the basics have been covered I would like to get a little more in depth in troubleshooting board components that may mimic the lack of outgoing power when a small inductive load from the main transformer is applied. I really don't want to just swap the pc board, if I could narrow the failed components down I would like to take a shot at repairing it.

I'm not an electronics tech but I have been an electrical troubleshooter for 20years.

Thanks for all you help thus far, I really appreciate all the input I can get.

[Meltedmetal]

Okay, and the input voltages are still there in the failed condition. Sure looks like something on the main board. Without a board diagram I'm out of ideas. I guess you could still try freeze spray on suspect components. If you study the board traces you may be able to figure out what drives what. Seems odd to me that everything but the fan loses power. I guess there must be a main contactor(relay), that turns the weld current to the torch on/off, mounted on the main board? Is there power to/from/though it in the failed condition? I am now officially in over my head but if it was mine I'd look at the board too. Hope you can get it working.---Meltedmetal

[adamstracy26]

Yeah I guess I'll start following the traces and see what I can come up with.. Thanks a bunch for all the ideas, I appreciate the help.

[Popscott]

Is there a constant 24 VAC at RC1, pins 2 & 3.

Does mildly tapping the board produce any results?

Does LED D29 stay on? ( +15 volts DC operational ).

[adamstracy26]

Anyone have any experience with these boards? Any checkpoints to focus on. This board is a two sided trace board with sizeable relays that cast a big shadow when trying to follow traces.

Any my help is greatly appreciated