XMT304 throwing breaker when switch is turned on. Help!

[blue66tang]

Hi guys, I am working on a xmt 304 cc/cv and need some help. I posted over on another forum, but have not been able to get as much help as I need. I recently bought a 304 at an auction. I got it home, plugged it in flipped the switch on and boom breaker popped. Checked wiring and such, and still the same thing. Pulled the cover off and discovered VR1 is cooked. So I spent the next few days trying to get my hands on a tech manual. Well I finally got one today and took the machine along with the manual to my electronic gooroo brother. We started doing the pre power check and disovered right away the SR1 and on/off power switch is bad along with the VR1. So i will be ordering those parts to replace them. However, what else do I need to be looking at. Is there something else that we are missing that could have caused these parts to go bad, or did these parts cause anything else to go bad. I really don't want to replace the parts only to have it happen over again. Any help will be greatly appreciated.

[blue66tang]

Dang, not one even looker.

[Broccoli1]

Weekend

[elvis]

Cruizer will be in on Monday. Also, post up a serial number so that he can get the right tech manual in front of this to help out.

[blue66tang]

The serial number to my machine is LB277886. Thanks.

[NHTIG]

Obviously a short circuit somewhere beyond the last burnt component. MAYBE the incoming service was hit by lightning in its previous life. Hard to determine. One would think that an internal short would have popped the breaker in its former life.
Unless it was wired with the wrong size breaker or a breaker was not used. Unfortunately, as I am sure your brother told you, these things can be a nightmare
to troubleshoot. He will need the tech manual and lots of patience. I did this for a living for many many years. It was fun and also SUCKED a lot of days. Maybe you will get lucky and there will be some know "generic" problem with that particular machine and someone in here will know the answer to the mystery.
In general when "light weight" components short they usually burn open and can be easy to find. In your case maybe a shorted "stud" diode?? Worse case a transformer. Sorry I did not have the correct answer and that a lot of this is just me thinking out loud. Retired now and actually miss the mystery of component level troubleshooting. Good Luck.

[NHTIG]

Maybe you have it already but there is an owners manual available for that on this site. Within it is a schematic that might help to some degree. Again, Good Luck.

[blue66tang]

Yeah I was able to get my hands on the Service/Tech manual. We did the pre power check and everything checked out ok other than the on/off Switch, SR1 and VR1. So I am in the process of at least getting those shipped.

[cruizer]

SR1 is likely blown, as well as do dads on your output board

[cruizer]

Your going to need that board that sits on your SR!, Another thing after your output board is your top board, generally the pulse trasnformers are trashed. These fire the IGBT's. Best take it into a qualified tech

[blue66tang]

Your going to need that board that sits on your SR!, Another thing after your output board is your top board, generally the pulse trasnformers are trashed. These fire the IGBT's. Best take it into a qualified tech

Hmm. Do you have anything that will tell me what the specs are on the boards. The sr1 board looks ok with nothing discolored, blown, ect. The SR1 itself is dead shorted between the terminals. I would also like to get my hands on the specs for the PC2 board as well, but miller said they didn't have anything. I most likely will not take it to a qualified tech, I work on everything myself and the few times i have taken anything to "qualified" techs has turned out to be a mess. I did call my local tech and he just wanted to replace a whole bunch of parts with out even checking them. Sounds like he didn't even know how to check them, which makes sense since none of that info is in the tech manual. Fortunately for me my brother works at a electronics development firm so he will be doing most of the checking/work for me. Just getting my hands on the specs is the hard part.

[welderdoc]

xmt

as cruzer said you should take it in. I have repaired a lot of xmts thru the years. most likely your looking at power switch, input rectifier, igbts, inter connect pc board for starts.

[cruizer]

Well, just check the 2 little protection diodes down low on the board next to each of the igbt's. If they are good, then likely so are the igbts. SR1 gets taken out by a surge. so now you have phase to phase, main breaker blows. Its unlikely but posssibly that the linking contactors are stuck. Extremely rare though. Miller doesn't like me too much when I send the spec's, though I can answer your questions any time you like... Best check your input switch, hopefully that will be the culprit

I fix 1000's of these units, pretty easy really

[blue66tang]

Well, just check the 2 little protection diodes down low on the board next to each of the igbt's. If they are good, then likely so are the igbts. SR1 gets taken out by a surge. so now you have phase to phase, main breaker blows. Its unlikely but posssibly that the linking contactors are stuck. Extremely rare though. Miller doesn't like me too much when I send the spec's, though I can answer your questions any time you like... Best check your input switch, hopefully that will be the culprit

I fix 1000's of these units, pretty easy really

How do i check the protection diodes, I don't have any specs on the board. They look nice and clean. The whole machine looks nice and clean other then where the vr1 blew, and the on/off switch blew. My brother was saying it looked like a surge as well. Today, I was messing around with it and disconnected the leads off the sr1 board so it could not pass current to anything else. I then proceded to plug it in, and boom. Blew the breaker. I then isolated the on/off swith and nothing. I then bypassed the on/off switch and it blew the breaker again. So I know the short is in the sr1. Now the big question is if it damaged anything else I am missing.

[Osar]

XMT304 throwing breaker when switch is turned on. Help!

I have an xmt 304 doing the same exact thing. So far, I have confirmed the switch is bad and there is a direct short between phases. No tech manual yet so it's tough to diagnose. LB241697