I'm a little late to the party (been browsing this thread off and on and enjoying reading your adventures!), But I would recommend doing a pre-power check before plugging it in again, if you are comfortable with a DMM (digital multimeter).




If you decide to open it up and start working on it, BE VERY CAREFUL! There is a lot of power stored inside the capacitors and the possibility of electric shock, or being hurt by exploding components is very real. Always wear safety goggles when the cover is off, and test the main capacitors to ensure they are discharged before touching anything else inside. When a part fails, it can explode and send debris flying faster than you can react and get away from it.

 

Ok, I can send you info from my manual as needed. Here's what it says for Help 2 and 4





My guess is that you have a problem with display board PC3. It seems unlikely that the thermistors on both sides would fail at the same time, unless it was caused by failed IGBTs. I would definitely recommend going through the pre power checklist before replacing any parts based on the help codes.

 

I can PM you with the pre power info if you want

 

That'd be awesome. Thanks. Also, for help code 2, it says see section 8-11? What is that page about? Thanks!

 

Section 8-11 is testing information for display board PC3. But you're still a little ways away from needing that!

Do you have a DMM?

 

You're right, I have to figure out how to get to that board and get it out first! LOL

Yes, I do have one. I don't like buying a little El cheapo ones, I've got a pretty decent one.

 

Leave the machine unplugged for a day before working opening it. That will give the capacitors a chance to discharge on their own. Then, when you first open it, set your DMM to DC volts and test across the terminals on each input capacitor. If any significant voltage is present (more than a few volts), leave it for longer before working on it.

 

Familiarize yourself with all the components before taking anything apart. See if you can identify the three main circuit boards PC1, PC2, and PC3. Then look for the IGBTs and output diodes. Look for the thermistors. Post pictures if you need help identifying anything and feel free to ask questions if you want advice on removing a part.

Out of curiosity, what is your machine's serial number?

 

Wise words worth repeating.

 

materthegreater, you inbox is full! He is my last message to you.

I believe I found a short on IGBT PM1. In your book it would be section 7-5. Instruction number three. Check C1 to E1, and C2 to E2 on PM1 and PM2 for no less than 100 ohms. 0 ohms indicates a short. PM2 passed with flying colors. PM1 has 0 ohms between E2 and C2. What does this mean? Bad board?

 

Sorry, this forum has tiny PM boxes haha!

Yes, that would indicate a bad IGBT.

 

I also found this sitting underneath PM1. Looks like a broken part of a component.



Also, when following the pre-power checklist from the technical manual, it had me test the capacitors. I was not 100% sure how to do this. The book said to test all three capacitors for a short. So I assume this meant to test resistance on each capacitor individually from one post to the other. If I did this right, the tank capacitor has an open circuit. Here's how I tested the capacitors.

I tested for ohms on every setting that my meter has. Not on this particular capacitor, but the one big one down to the right that is not shown in this picture was the shorted one. It is the tank capacitor. It showed no resistance.


I also tested all four diodes on the PC-2 board as instructed by the manual. Three out of the four read either way too high or way too low.

 

That part definitely goes to the IGBT's. They are both blown out of the side and broken. You reckon this has something to do with my problem?

 

Well, I looked up the serial number on Miller's website, this welder is from 1996. Gonna be difficult to find new IGBT's. Gonna try though!

 

Well, you're still alive, so that's good. I'm sorry for your discovery, but am not the least bit surprised, as the IGBTs was what I thought might be the problem from the beginning.

Good for you for finding the blown off piece that has the part number CM100DY-12H. But don't bother looking for that part number.

Miller discontinued those particular IGBTs. Look no further than your own machine for the reason why.

Miller re-specified a different IGBT as a replacement, and the new IGBT is a CM75DUM-12F.

You need to replace ALL of the IGBTs, not just the one that exploded. The kit from Miller is $900.00.

I've seen eBay specials from LongShen in China for as little as $25.00 each.

If it were me, in your shoes, I'd button the cover back on your Miller XMT304, and set it aside. Write down some notes on these part numbers, print out a few photos you took of the guts, stick your notes and photos in an envelope, tape it to the machine, and get back to learning how to weld with the AC transformer that you already bought and paid for, that is rock solid, dead simple, doesn't have any fancy whiz bang, and I do mean "BANG!" electronic components that are expensive to replace... and get back to welding.

I never ceased to be impressed with what you take on, but you can replace every one of those IGBTs, and still find that you need to also replace one of the circuit boards too.

Before becoming a welding machine repair technician, get confident with the AC machine that you have, and as you get into it, you may find that another DC machine, at very low cost, manifests itself into your orbit.

That being said, count your blessings to have Glen by your side on the XMT. MatertheGreater's assistance is yet another manifestation of goodwill!

So many choices!