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nates
02-26-2007, 10:04 AM
So I'm going to be picking up a non-working AC/DC Miller Thunderbolt today. Owner says that when you turn it on it makes a sort of loud buzz, like it was under a heavy load, and will arc but not enough to melt metal. Even though I haven't got it in hand yet I thought I would run it by you guys to see what you thought it might be first. It's basically free, so I'm not worried if it's unfixable. What do you think?

Hobart Expert Keith
02-26-2007, 10:22 AM
Could be that one or more of the output diodes are shorted. Also check the adjustment of the shunt assembly to make sure that it is not loose.

Keith

smyrna5
02-26-2007, 10:27 AM
So I'm going to be picking up a non-working AC/DC Miller Thunderbolt today. Owner says that when you turn it on it makes a sort of loud buzz, like it was under a heavy load, and will arc but not enough to melt metal. Even though I haven't got it in hand yet I thought I would run it by you guys to see what you thought it might be first. It's basically free, so I'm not worried if it's unfixable. What do you think?

There really isn't much to these beasts. If it were me, I would study this diagram then check all the parts for shorts one at a time. Then, I would probably check all the parts in the DC section to the right on the diagram looking for shorts or open circuits. If you put the switch to AC High only and the loud buzz goes away, or the welder works ok, you will know the problem is in the DC circuit, labeled SR1 in the diagram. If it doesnt work on AC or DC i would suspect a transformer problem, but it could also be a bad swich at S1 or the fan motor (FM) could be shorted out. Or, Since SR1 is connected across the secondary of the transformer, it is also possible that a short somewhere in the SR1 circuits would cause it not to work even on AC HIGH. I would probably see if there was a connector somewhere that would let me completely isolate SR1 for testing purposes. (look at the parts diagram).

http://www.atlantamusclecars.com/Paint/Stickmate.png

OF course any component that looks burned is automatically suspect. I have used the stickmate diagram, since they are supposedly the same.

MrSmucker
02-27-2007, 02:57 AM
So I'm going to be picking up a non-working AC/DC Miller Thunderbolt today. Owner says that when you turn it on it makes a sort of loud buzz, like it was under a heavy load, and will arc but not enough to melt metal. Even though I haven't got it in hand yet I thought I would run it by you guys to see what you thought it might be first. It's basically free, so I'm not worried if it's unfixable. What do you think?

Sounds a whole lot like the one that went out on me. I found that one of the bushings where you plug the cables into had cracked, melted, broken or got damaged in some way, and it was doing just what you described, put under a heavy load. So heavy in fact that it melted the connecting wires inside. I was able to crimp a few of them back together, and continue using the machine, but lost several temperature ranges, and I lost the AC function all together.

I was never able to determine the reason for failure, but it went from running perfect to just as you discribed while I was no where near the machine to physically break it, but after making a lot of continuos welds, likely greater then its designed duty cycle.

nates
03-03-2007, 04:44 PM
So I picked up the welder and everything looks decent inside. I was fiddling with my multimeter and was checking for conductivity between my electrode plug and work/ground plug and it showed connectivity on the ac side (little beep went off). Is that normal? Connections all look good otherwise, nothing cracked or burned.

Mike W
03-04-2007, 12:23 AM
Set it to AC high and measure the voltage at the output. I would expect to see 80 volts AC or maybe a little less. If that is ok, set it to DC and measure the DC voltage.

nates
03-04-2007, 03:08 AM
This is the old style that doesn't have any switches other than off and on. I'll check the ac voltage tomorrow, but I'm a little wary about turning it on when there is a problem (don't want to burn anything up).

Pin Head
03-04-2007, 03:16 AM
Owner says that when you turn it on it makes a sort of loud buzz, like it was under a heavy load, ?

"Buzzing" is pretty normal for these welders, which is why they are often called "buzz boxes".


I'm a little wary about turning it on when there is a problem (don't want to burn anything up).

It's already broken, so turning it on isn't going to make it more broken. If it starts smoking, you can turn it off.

nates
03-04-2007, 02:23 PM
So on powering up, it indeed does buzz pretty loud. Things that I noticed are that
1. The fan sound horrible (rattles around alot).

2. The buzzing isn't that bad.

3. My breaker tripped after 10 seconds (no welding).

I'm still wondering if I should be getting continuity between the electrode and ground jacks on the front AC panel. And I checked. The chassis is not conducting.

The main thing that I'm starting to suspect is that the guy I got it from said he had to put in a power cable, and I'm thinking he may have wired it in wrong.

smyrna5
03-04-2007, 02:57 PM
So on powering up, it indeed does buzz pretty loud. Things that I noticed are that
1. The fan sound horrible (rattles around alot).

2. The buzzing isn't that bad.

3. My breaker tripped after 10 seconds (no welding).

I'm still wondering if I should be getting continuity between the electrode and ground jacks on the front AC panel. And I checked. The chassis is not conducting.

The main thing that I'm starting to suspect is that the guy I got it from said he had to put in a power cable, and I'm thinking he may have wired it in wrong.

It depends on what you mean by continuity. Assuming you have it set to AC Only you are measuring the resistance across the output side of the transformer. I don't have one to measure, so I don't know exactly what the resistance of that set of windings is, but I doubt it is very high, since you are measuring the resistance of probably less than a few hundred feet of wire. If you are using one of those multi-meters that have a continuity check it could very well give you a sound. It would be far better to measure the actual resistance reading across that set of terminals and tell us what that is.

Since you have the schematic and suspect somebody wired somethign wrong, why not just check the wiring against the schematic. There aren't many parts in it, so it shouldn't take you very long. I would check off each connection as I verified it.

Zrexxer
03-04-2007, 03:07 PM
"Buzzing" is pretty normal for these welders, which is why they are often called "buzz boxes".Under load. Not when just powered up. The only thing you should hear when powering up an idle transformer welder is the fan, and even that shouldn't be making too much racket.

It's buzzing under no load, and trips a breaker under no load. Something's shorted. Oh wait... Hobart Expert Keith said that waaaaay up the page.

Thomas Harris
03-04-2007, 03:17 PM
Hope it ain't shorted inside the transformer windings.

nates
03-04-2007, 06:44 PM
Ok, so advice on how to go about checking for a short?

Pin Head
03-04-2007, 11:20 PM
Disconnect the DC side by removing the connections from the transformer to the diodes and try it in AC mode. If it runs, then the short is in the DC side. If it pops the breaker in AC only, the transformer is likely shorted.

old fart
03-05-2007, 12:45 PM
Do what pinhead suggested and if it turns out to be the DC section seperate each of the diode leads and do a resistance test on each one. ( using the diode function on your meter of if it is analog, measure resistence in one direction and then reverse leads and chcek again. . Should be high one direction and low the other. If not the diode needs to be replaced.)
O.F.

old fart
03-05-2007, 12:46 PM
Do what pinhead suggested and if it turns out to be the DC section seperate each of the diode leads and do a resistance test on each one. ( using the diode function on your meter or if it is analog, measure resistence in one direction and then reverse leads and chcek again. . Should be high one direction and low the other. If not the diode needs to be replaced.)
O.F.

nates
03-05-2007, 08:18 PM
Woohoo! Progress. I disconnected the DC end of things and it worked just fine in AC mode. I appreciate the instructions on diode testing, now if I can just figure out what they look like.

nates
03-05-2007, 08:44 PM
Figured it out. Checked the diodes. One of the red sleeved ones read .4 both ways on my MM's diode function (didn't even know I had one). All the others looked good. Are they expensive? Where should I go about getting one? Is it something my local dealer would have? Thanks again guys!

nates
03-05-2007, 08:49 PM
oh and would that one be straight polarity or reverse polarity?

smyrna5
03-05-2007, 09:22 PM
Figured it out. Checked the diodes. One of the red sleeved ones read .4 both ways on my MM's diode function (didn't even know I had one). All the others looked good. Are they expensive? Where should I go about getting one? Is it something my local dealer would have? Thanks again guys!

Diodes shouldn't be expensive. Most electronic parts have numbers on them. With that you can probably order one from an online electronic supplier. It would probably be easier to contact Miller and ask if they sell them as replacement parts.

Different welder, but see this post

http://www.hobartwelders.com/mboard/showthread.php?t=14505

Congratulations on tracking it down.