Hi everyone I hope all is going well and safe with everyone,I just had some quick questions regarding my new to me Miller Shopmaster ac/dc unit. This unit powers on just fine but has no output at the terminals in either cc or cv modes is there any recommended checks I could perform as to figure out why?? I grabbed this machine for $200 figuring why not and I came with a feeder and nice tig setup so I’m not that bummed about it but would love to actually be able to use it if possible. Thanks for any pointers in advance ohh and the serial # is KB100628
Guess I will start by checking out the capacitors in back since those seem to be a likely culprit. The inside of the machine looks fairly clean and un-abused which I guess is a good thing considering it’s about 30yrs old
Well I just looked over the pcb board and it still looks like new. Really wish I had a little more experience with these transformer welders. Gonna go ahead and take the capacitor bracket and caps out now
cap bank is only in the CV circuit, not used in AC or CC.
Look real close at the AC, CC,CV switch blades. see if any are burnt.
3 common problems. Burnt CV points in switch, Cap bank blown and pcb dies.
Switch and pcb are obsolete from Miller. You will have to find some way to repair them. Cap bank can be rebuilt with out much problem.
Start checking the panel switches find the remote voltage/current switch. then check the contactor switch. use ohm meter and make sure they open and close.
if the contactor is in remote it needs the feeder to turn the welder output on.
The voltage/current switch in remote needs a foot control or the feeder needs a voltage control pot. try this with the voltage/current switch in remote and the mode switch in CC. measure sockets c and D in the 14 pin plug. should be 0 to 10vdc depending on where your output knob is set. If no voltage, check the diagram on the side panel and measure the 18 and 10 volt AC power supplies to the control pcb.If they are there the pcb has failed. Check RC51 pin 5 to case ground should be 24vdc. If you have the 10 and 24vdc then check RC55 pin 2 to ground should be zero unless you are welding. then it will be 1.6vdc per 100 amps of current.
If you have voltage here the hall device is bad and the hall device might not be repairable. molded blocks of plastic can't be repaired. if mounted on a pcb it is a maybe. Let me know what you find by private message and we will see if there is more to test. You will need a good volt/ohm meter and possibly an oscilloscope to check for gate pulses.
Thanks for your reply it is greatly appreciated ccawgc. I went ahead and ordered an oscilloscope because I figured I will need one again someday, all of the caps looked physically okay but I need to actually test them to be sure. I’ll go ahead and start running those other tests after work today thank you
Well I believe i've tracked down the culprit, I tested voltage on the RC55 plug pin #2 with my amps and and arc force set at zero and it was reading about 4vdc which according to ccawgc indicates a faulty hall device. ive got a couple pics of the unit and also a replacement part I am considering so any feedback would be appreciated, will this work??
Well it turns out the Shopmaster ac/dc had a faulty LEM and pcb so rather than get it repaired for more than I paid for it I gave it back to the original owner in exchange for this monster it’s a Lincoln TIG 300 single phase unit that spent most of its life in a military shipyard shop with regular calibrations and up to date replacement parts (except the water cooler that came with it) gonna go ahead and wire in a new plug and double check for any corrosion or faulty wires and see what it does this weekend.
I’m more of a Lincoln guy anyway lol, just curious if there are any critical areas on this machine that I should check before powering up after sitting for some time?? Any pointers are much appreciated
Remove the covers, and make sure nothing has been living inside.
with bright light make sure nothing is burnt or damaged.
across the front where the warning label is, remove that cover, the pcbs are behind it. Make sure the fuse on the left pcb is not blown and nothing is burnt.
white resisters that look brown are normal with age. should be ok.
If the code number ends with a C. look for the PFC oil filled capacitors.
Make sure they are not blown or leaking. Set jumpers on reconnect panel to correct line voltage and power up. Left pcb is the reactor control and the right pcb is the timer pcb. ( gas valve and HF). Take the code number minus any letters to Lincolns web site. under support find parts tab. select and go to the public service navigator.
enter as a guest. put code number in the box and select your machine.
most of the repair information is there.
That has to be a pretty late model Tig 300/300. Looks a lot different than the big tall older ones. Wonder if it uses less power? I think the older ones required a 100 amp breaker.
Ohh before I forget I have a big ol 3-phase Linde tig and stick machine I would be willing to “give” away to whomever can make it to me in the Pacific Northwest tacoma area. It’s a 301 CC
Good future reference. I have one of the last two units that were in the wharehouse.
"Where's Stick man????????" - 7A749
"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55
"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding "Stick-man"
Fired up the TIG 300 this morning and struck an arc, welds really smooth in stick mode. Thank goodness I took that Shopmaster back that would’ve left a real bad taste in my mouth for some time. Now I need to start piecing together a torch/remote and maybe an updated cooler. Guess I could just do some lift arc air cooled tig welding for now. Ohh and just for reference purposes I’ll throw a pic of serial and input. I ran it off a my 60amp breaker to start and I did ok but I’m sure if I were running bigger rod or higher amp it would’ve tripped.
odd on the code number, both numbers relate to the tig 300/300 minor differences.
The C stands for factory installed PFC capacitors. M is factory installed meters.
according to data plate 300 weld amps will pull 82 amps on a 230 volt line.
a 245volt line will need a little less. But with PFC caps it will appear to draw 60 amps all the time the welder is powered on.
I noticed that as well where it looked like it was originally a 4 then changed to a 2? Curious. The other welder option was a gray Lincoln Tig 300 that didn’t have the digital meter but all of the other controls appeared to be the same.
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