Cst 250

[toolman]

Machine has no out put.
Old machine I have had it along time. I hate to take it to a service center and spend money on it. But if someone has some information here. I will be willing to try to repair. I have always heard they are expensive to repair.

Thanks in advance.

[ronsii]

Machine has no out put.
Old machine I have had it along time. I hate to take it to a service center and spend money on it. But if someone has some information here. I will be willing to try to repair. I have always heard they are expensive to repair.

Thanks in advance.

Have you been through the manual and checked the setup and troubleshooting sections? also, is this an issue that just happened suddenly? or when welding? hopefully user ccawg will see this thread and give you more info on problems and fixes with it

[Welder Dave]

It's not that old of machine considering there are machines from the 30's still in use and 1000's from the 60's and 70's still earning their keep.

[ccawgc]

We need a lot more than no output. Does it turn on? and lights on or flashing?
Remove cover and check leds on the pcbs. Check for any broken weld leads inside the case. Now be very very careful with cover off. Do all inspections on a welder that has been turned off over night and UNPLUGGED. Check all pcbs for burnt spots.
Then you can turn on and check for LEDs on the pcbs. Stand in back of welder and turn switch on. try to stand back a full arms length wear a face shield.
The 250 might have a large fuse on the pcb. It protects the welder against 460 volts when set to 230 volts. If blown you have two choices. just replace the fuse or buy from Miller the PTC replacement kit and never have to change the fuse again.
mounts to the fuse holder.
Not being able to see or put my hands on the welder I need as much information that you can find. Down load the owners manual and go through the trouble shooting section.

[toolman]

First thanks for the reply.
It has been down a while and i have tryed the manual trouble shooting in the past.So it will be best if I go thru the process again and report back to give the best answers I can.
I will get back quickly.

Thanks
Tim

[toolman]

Removed the covers done through inspection. Found nothing loose or burnt.
Plugged it in turned it on. Yellow light come on and goes right back off. I can hear an adubile click and the blue light flashes continuous. Turn it off the blue still flashing and the fan runs for a short time fan and light stop. I checked the input voltage 125 volts on each leg and 250 together it is linked for 230 volts.

Thanks
Tim

[ccawgc]

Your symptoms point to incorrect line voltage either to high or to low.
The welder will work on 230 volts plus or minus 10%. That means 253 is the highest voltage it might run on when set for 230 volts. If your line voltage is 250 volts it is a little on the high side. you may want to talk to your power company.
Two things. try your welder at a different location and second try measuring with a different meter. Try a place with voltage that measures 245 or below.
If you still get a flashing blue light on the lower line voltage then one of the pcbs is failing or the LEM.

[toolman]

Thanks
I stopped working in my brothers shop. He had used it many times. So I brought it to my shop and the results are the same. So it`s probably pcb or LEM.
I have no idea what LEM stands for. Please explain.
In the trouble shooting section it says a factory reset is needed . What does that mean repair?

Thanks,
Tim

[ccawgc]

LEM is the brand name of the hall device current sensor. When they fail they drag the 15 volt power supply down and cause other symptoms. The reset they are talking about is not a factory reset. but a machine reset by turning power off and back on.
Some faults are what they call latching faults and will lock up the welder until the power is turned off. supposed to get it repaired before turning it back on.
LEM is connected to RC5 on the inverter control pcb. measure from system ground.
white and black should be 15 vdc plus and minus polarity. Red and shield should read zero. when working red will read 1 volt per 50 amps of weld current.

[toolman]

Done the check as you described.
White 0 VDC
Black 14.97 VDC
Shield 0 VDC
Red 14.00 volts DC

I checked multiple times to make sure my readings are correct.
I checked the white wire to make sure it wasn`t broke it is fine.
There's were all read from the solder joints on the back of the board.
Pulled the board and did a visual inspection no problem were visible.

So the white and red are out of spec.

[ccawgc]

voltage on the black wire should have been minus 15 and the white wire Plus 15.
red wire should have been zero. the shield or bare wire is connected to case ground.
make a note where each wire is. with power off unplug the LEM cable.
Retest and see if the pcb can supply both plus and minus 15 volt dc.for the white and black wires. Place black meter lead on ground and red to plug.
If so the LEM is bad. if no voltage on the white supply a pcb is bad and the LEM may be bad also. Step back as you power up in case something dies.
Also if it is the LEM, with it unplugged it may power up correctly and have output.
But don't try to weld as you will have full output with out any control. May damage the welder.

[toolman]

The black was minus 14.97 VDC white was 0 and the shield was 0 the red was 14VDC
I will check again and try your process

[toolman]

Retested with LEM unplugged black
Black minus 14.97
White 0
Red 14VDC
Shield tested for continuity to ground. Good
Unplugged the harness from the board and checked each wire for continuity no broken or loose wires
With LEM unplugged still has a continuous blinking blue light.
Thanks

[ccawgc]

It looks like the Lem may have failed and damaged the pcb. you are missing the +15 volt power supply on the pcb and the feedback connection should be 0 and it reads 14 vdc. Try doing an ohm test on the LEM terminals see if any are shorted, all should be over 1000 ohms.

[snoeproe]

It's not that old of machine considering there are machines from the 30's still in use and 1000's from the 60's and 70's still earning their keep.

This is an inverter that hasn’t been produced in quite some time. It was long a go replaced with the cst 280. There was a long list of problems that developed with the cst 250.

[toolman]

I have Fluke T5 which is pretty basic auto ranging meter. It show zero ohms. I was moving the leads to different contacts it has four. So I tried a craftsman meter that has ohms setting from 200 to 2000K.
Nothing shows on the meter,with set on 2000.
I may not be doing it correct.
I will post a pic of the 4 terminals I was testing.

Thanks
Tim

[toolman]

Can't add a pic.

[toolman]

This is an inverter that hasn’t been produced in quite some time. It was long a go replaced with the cst 280. There was a long list of problems that developed with the cst 250.

Not sure of the problems with the CST250. But this machine served us well for many years under heavy use. If I have to put it in the dumpster I have no regrets.

[ccawgc]

I think were done, The pc1 205772 is obsolete. time for a new machine.

[toolman]

I think were done, The pc1 205772 is obsolete. time for a new machine.

Thanks for your time I very much appreciate.
I had looked that part and seen it was obsolete also and thought that was where we were heading.

Thanks again.
Tim