MM 350p trouble shooting help

[E350]

I blew the dust out but am still having problems with my Millermatic 350p. This is what it is doing:

Starts up properly: shows MM and 350p;
Then goes to last used setting: 19.0v / 180wfs;
Then I weld for a minute or two and performs very good;
Then set the gun aside;
Then after 2-3 minutes, the machine goes dark;
Then restarts on its own: shows MM and 350p
Then goes to 21v / 400wfs;
Then machine goes dark again and then restarts itself
Then goes to 21v / 400wfs and will repeat this cycle until I turn it off. Millermatic 350P

I also had one Help 3 trouble shooting code.

Year Mfg: 2007/Jan. LH010001 Style: LH01
Model: Millermatic 350P
Stock No.: 907379
Serial No.: LH480282B
Stock No. 907379
Serial No.: LH490232B
Bernard® Q300 mig gun

Aeronca41, thank you for your response. I can't remember why my notes and specifications file has two different serial numbers for the machine. I will inspect the machine again for their location and update this post.

Anyone experienced this before and fixed it?

[Aeronca41]

Please post your serial no.

[E350]

Aeronca41, thanks for your response. See edited initial post above.

[Aeronca41]

The two LH4xxxxxx numbers both lead to the same manual, and the LH0100001 got no hits, so this is probably enough info. I don't know enough to be much help with this question, but the guys here who do know need the serial no to look it up, so I asked to at least get that step toward an answer. Wish I could be more help. Hope one of the wizards sees this and has some ideas.

[gnforge]

If it were mine id pull covers, check & tighten nuts on input wires. Then I'd unplug all connectors blow out & plug back in, one at a time. Inspect each connector for signs of heat etc. inspect boards for signs & put back together. <br />
One other thought. I'd pull apart & inspect both male & female plugs where plug into wall. <br />
I had one leg come loose on my male plug sometime back but just can't remember how it acted or if coded. But once fixed ran like new.

[H80N]

If it were mine id pull covers, check & tighten nuts on input wires. Then I'd unplug all connectors blow out & plug back in, one at a time. Inspect each connector for signs of heat etc. inspect boards for signs & put back together. <br />
One other thought. I'd pull apart & inspect both male & female plugs where plug into wall. <br />
I had one leg come loose on my male plug sometime back but just can't remember how it acted or if coded. But once fixed ran like new.

+1 ... Good Thoughts..... Provided the OP is confident & competent enough to do it

[E350]

gnforge Thanks, that is troubleshooting. Learning to see is the hardest part of any endeavor and my guess is that if I unplug the machine, take my time, I might find the problem. I will start from the outside first with everything which comes in contact with me the user, the gun, the liner, the connection for the trigger and the a gun line. Tonight, I was able to use the machine for quite a while before it turned itself off and started the cycle. It was interesting because as long as I kept an arc going, it seemed to prevent it from cycling as described above. Once I put the gun down to do some grinding or fabrication it would cycle. I replaced the trigger in the gun a while ago after it first started doing this. So I will take the gun apart and inspect and likely replace the liner, etc.

H80N I am not that confident or competent, so I will go slow and if I see anything unusual, I will snap a picture and post it here.

Thank you guys.

[Aeronca41]

If it were mine id pull covers, check & tighten nuts on input wires. Then I'd unplug all connectors blow out & plug back in, one at a time. Inspect each connector for signs of heat etc. inspect boards for signs & put back together. <br />

One other thought. I'd pull apart & inspect both male & female plugs where plug into wall. <br />
I had one leg come loose on my male plug sometime back but just can't remember how it acted or if coded. But once fixed ran like new.

Nicely stated. I'd do the same thing but didn't think I could describe it well enough to be a help. Just might add that is possible there could be charged capacitors in there even with the plug out. If you see any large aluminum cans, generally covered with plastic, don't touch the terminals or anything they're connected to. There are bleeder resistors in the design to discharge them, but if one of those should fail and you touch the cap, it can be exciting-in a bad way. :-)

[E350]

Aeronca41 I was wondering about that. Thank you for describing their appearance. I wonder if schematics or even shop service manuals are available for the machine...

[Aeronca41]

Glad it was a help. It's always good to be aware of something that might bite you.

Assumed you had the owners manual, but if not, here it is. There is a schematic but no details on the circuit boards. Miller does not generally make repair manuals available except to their techs. Very hard to come by. If you look on this web site under "Support" you will also find a parts manual for your machine.

https://www.millerwelds.com/files/owners-manuals/O1327X_MIL.pdf

[gnforge]

If it is going blank and shows mm 350p sounds like it is restarting or starting from off. <br />
Problem shouldn't be in gun as that is just a switch i.e. Contacter <br />
If a contact becomes loose it will heat during use like welding then cool when not using as in stop welding. When cools sometimes will loose contact or drop voltage to low. <br />
That is what would lead me to check input wiring first. <br />
If you know someone you can trust that is qualified to inspect. I would still check wall plug and plug on end of input cable then simply pull cover and there is a panel where the input wire comes in with nuts that hold eyelets down. Check them for tightness and corrosion. <br />
Had this happen to mine couple years ago, it was very similar. <br />
All in all pretty simple to do if breaker is OFF. <br />
Any electrician could do in 1/2 hour if u had cover off. <br />
He could also check and blow out your other connectors in no time if he is trustworthy. <br />
Just a thought. Hope it helps. Good luck

[E350]

gnforge by input wiring I assume that mean the wiring from the plug to the machine where it connects in the machine. If so, I will check that. In fact I will check from my 240v receptacle (I wired it) to my plug (I wired it) to the inside where it connects to the machine. And yes, I will turn off the circuit breaker and check the receptacle (with a light or multimeter) to assure that the receptacle is not hot before proceeding to check the receptacle. BTW, I just recently moved the machine 100 miles on a bumpy highway (CA does not spend money wisely on infrastructure), so it is quite possible that some connection vibrated loose. To your credit, you are not alone advising to look for loose connections. Here's what the Miller service tech said this morning:

"It sounds to me like there is a connection issue between the main control board, and the front display board. I would suggested picking up some electrolytic grease (we use nyogel) from your local auto parts store and apply the grease to the following locations.

PC1, RC11

PC3, JP5

Regards,
John Herek
Service Technician, Commercial Solutions Division"

What a great company Miller is! I am so happy to receive a helpful email from Miller customer service rather than just being treated like a mushroom.

I repost the MIller tech's advice here with my full understanding and a warning to others that it is my/our individual responsibility - and any others who read this -- to be safe - it is not Miller's, it is not this forum's, it is not mine or anybody else who posts in this thread. An arc welder is a very powerful source of electricity. Proceed at your own risk or have a professional service it for you!

Edit: Aeronca41 the manual you linked has a wiring diagram in the back which shows the location of the pc board interconnects, etc. which the Miller Service Technician referenced in his email to me. Thank you buddy, that will be very helpful!

[Aeronca41]

I like the bumpy highway info--hope it means you're on the way to a nice cheap (no cost) fix. Those are the best kind! And once again, a great illustration of Miller quality support. These guys are a real standout from the crowd.

[gnforge]

Yelp that's what I meant. <br />
Hope ya find something

[E350]

Hey Aeronca41 what does this look like to you?