Xmt 350 os

[Alan J]

Firstly I would like to thank those who helped me out on my BB 400 CC/CV, it's working a treat ... I have now a miller XMT 350 OS that is crying out for some HELP, we didn't get the number, Once the machine cutout it would take about 10 minutes before you can get it working again

We only use it on stick process and its wired 3 phase, and I don't see it being a duty cycle problem !! I plan to use it on a small job in the shop and see if it happens again

The equipment is serial number MG1242215U, I have removed the surrounding cover and the machine is very clean, the fan rotates freely and I cannot see any discoloured wires.

Any advice will be highly appreciated

[ccawgc]

Does it display any help codes as the output turns off?
Did the fan turn on? 10 minutes to cool down almost sounds like a heating problem.
Help 3 or 5 are simple left or right side over temp. A help 25 is over duty cycle limit.
take 15 minutes to reset with fan running.
If you know how to use a voltmeter and test electronic equipment there are a couple of tests you can do. remove all the case screws and two from each handle.
leave cover in place. turn welder on count to 10 and turn it off.
Lift cover off and measure voltage at the two large capacitors. CAUTION could have up to 470vdc on each. with power just turned off the cap will be discharging.
Both should read about the same. if one stays high and the other discharges.
There is a problem with the caps and the interconnect pcb. you should get a help 8.
When the caps get to far apart in their voltage, the inverter shuts down to keep it from blowing up. Cap starting to fail damages a large resistor on the interconnect pcb. this allows them to get out of balance after a few minutes. Powered down for 10 minutes allows the high one to discharge enough so it will be in balance at next power up. your unit left miller on 3/23/2016 will be 5 years old in march 2021.
Protect your self when working on this welder with the cover off. the cap voltage will burn the ends off your meter probes if you make a mistake. a short on the caps could make them blow up. one more test is to look at the supply voltages to the hall device (LEM) near the positive output terminal. test at plug on control pcb. RC9 pins 3,4,5,6. six is ground, +15 vdc pin 4, -15 vdc pin 5, pin3 is feedback current signal.
1vdc = 100amps of weld current. should read 0 in standby. Make meter connections
then step back and turn weld on. try to stand in front. Never stand close and by the inverter section. If it blows you can not get out of the way fast enough.

[Alan J]

Thanks for the reply ccawgc,

I have a job to do using the machine so I will see if it lets out a help code to try and narrow down the problem before I start to open covers

[lacers123]

Does it display any help codes as the output turns off?
Did the fan turn on? 10 minutes to cool down almost sounds like a heating problem.
Help 3 or 5 are simple left or right side over temp. A help 25 is over duty cycle limit.
take 15 minutes to reset with fan running.
If you know how to use a voltmeter and test electronic equipment there are a couple of tests you can do. remove all the case screws and two from each handle.
leave cover in place. turn welder on count to 10 and turn it off.
Lift cover off and measure voltage at the two large capacitors. CAUTION could have up to 470vdc on each. with power just turned off the cap will be discharging.
Both should read about the same. if one stays high and the other discharges.
There is a problem with the caps and the interconnect pcb. you should get a help 8.
When the caps get to far apart in their voltage, the inverter shuts down to keep it from blowing up. Cap starting to fail damages a large resistor on the interconnect pcb. this allows them to get out of balance after a few minutes. Powered down for 10 minutes allows the high one to discharge enough so it will be in balance at next power up. your unit left miller on 3/23/2016 will be 5 years old in march 2021.
Protect your self when working on this welder with the cover off. the cap voltage will burn the ends off your meter probes if you make a mistake. a short on the caps could make them blow up. one more test is to look at the supply voltages to the hall device (LEM) near the positive output terminal. test at plug on control pcb. RC9 pins 3,4,5,6. six is ground, +15 vdc pin 4, -15 vdc pin 5, pin3 is feedback current signal.
1vdc = 100amps of weld current. should read 0 in standby. Make meter connections
then step back and turn weld on. try to stand in front. Never stand close and by the inverter section. If it blows you can not get out of the way fast enough.

Thank you for such a detailed explanation. I was having a similar problem. You gave me an idea and I fixed the problem.

[Alan J]

Thanks for the advice,

The first test on the capacitors, after the unit was on for 10 seconds and then shut off -BUS measured 134 volts and dropping to 0 + BUS 127 volts and dropping to 0

With the unit turned "on" RC9 Plug in board... 6 being pin closest to the front panel was ground and ok, pin 4 was +15.34 vdc pin 5 was -14.98 vdc ...

The fan is operational ...

Is it worth i put it on a load bank ???

[ccawgc]

Can't hurt, place cover back on. pick a machine setting that is at 100% duty cycle,
Then run welder on the load bank for 10 minutes let rest for 5 then run 10 minutes more. or you can run it at the 60% level. 6minutes on then 4 off then 6 minutes on.
If welder get through two cycles with out failing. The problem is not a thermal one.
Make sure you have 18 inches of free space in front and behind welder for clear air flow. Cap voltage looked ok. Dropping to zero volts in about the same time points to caps and discharge resistor all ok. Power supply voltages to the LEM are ok. Only other thing to test is the LEM calibration while on load bank. But you will need a DC clamp amp meter and good volt meter. To measure the LEM output and compare to clampmeter after math done.

[Alan J]

Hi ccawgc

Just getting back to the terminal RC9 on the board i did another check pin 3 to ground pin 6 and was getting 0.4 vdc across the range 0amps to 425amp, however, I'm not sure I was doing the test correctly.

My curiosity is leading me to a problematic capacitor assembly Pt No# 233668 which would trigger a HELP 8 ???? or am I'm missing something as im the measuring of the voltage between pin 3 and 6 and the small harness is disconnected. ??

[samll]

Thanks for the advice,

The first test on the capacitors, after the unit was on for 10 seconds and then shut off -BUS measured 134 volts and dropping to 0 + BUS 127 volts and dropping to 0

With the unit turned "on" RC9 Plug in board... 6 being pin closest to the front panel was ground and ok, pin 4 was +15.34 vdc pin 5 was -14.98 vdc ...

The fan is operational ...

Is it worth i put it on a load bank ???

I do not think load bank will make any difference
maybe it will do even worse

[danielplace]

I do not think load bank will make any difference
maybe it will do even worse

Isn't that what you looking for it to do ? act up under load ? what better way than loading it with a continuous controlled load ?

[ccawgc]

You want RC 9 plugged in. you will not see any voltage on pin 3 unless the welder is under load or the hall device has failed. Pin 6 to 4 and 5 are the 15 volt power supplies. one positive and one negative. need to see them around 15 volts with hall device plugged it. this will show both the power supplies and the hall device are ok.
If you powered on the welder with RC 9 unplugged the welder might display a help 8.
Help 8 indicates a problem in the secondary power system. output diodes or hall device, transformer. For testing a welder load bank is safer that a live arc.
Load bank must be set to the correct load for machine under test. With a live arc you can't hold it steady, you blind some one or start a fire or burns. Save live arc for final tests. you and then testing the arc stabilizer circuit.

[samll]

Isn't that what you looking for it to do ? act up under load ? what better way than loading it with a continuous controlled load ?

Makes sense