cutmaster 51 half power

[SWANSON]

TD Cutmaster 51 is cutting half capacity. Have control knob set to max amps. Placed amp clamp on workpiece lead and only reading 29 amps during cut. Found I have only 17vdc from auxiliary transformer. Should be 28vdc

Screenshot_20-5-2025_193729_.jpeg

Schematics show I

Screenshot_23-5-2025_63950_.jpeg

should be getting 28vdc

Contacted MCI transformers. Gave them part numbers from transformer tag. 11x420
4-44-8412
3905
They sent me print for my transformer. And it says 13vdc output.

unnamed.jpg

I am confused!!

[AREA]

I am not an electrician or claim to know anything about it but I did notice in your second screenshot that the transformer output should be 28 VAC not 28 VDC. If you were measuring output of the transformer with meter in DC mode I would expect to see 0 VDC but I don;t know. Just sayin. Would hate to see you replace a good transformer trying to fix it.

[AREA]

Your torch will have numerous smaller gauge wires feeding current to your electrode, on your machine they may be white in color but maybe not. Have you checked to be sure none of them are broken at either end or disconnected from the main PCB?

[SWANSON]

AREA thanks for your response. I don't know why I listed voltages as dc voltage. Thanks for the correction.
First screenshot.. Terminal J5 (pin 3. 17VAC ) (pin 2. GRD) (pin 1. 17VAC)
Terminal J8 pin 1. and pin 4. both 124VAC And also 124VAC after 0.5A fuse.
I cant access back of transformer as it is circuit board mounted. Otherwise I would check voltage at solder terminals.
I am leaning towards faulty transformer. But print from MCI transformer "last screenshot" dose not seem right? Would you agree?

[AREA]

I would agree that MCI transformer does not seem to be the correct one. Is it an MCI transformer in the unit?

[SWANSON]

Yes MCI 11x420
4-44-8412
3905
Will contact them again.

[SWANSON]

This is the print I received from MCI. Same transformer as original. Secondary voltage still 14vac. is it possible that one of the two secondary windings is bad. Also Is this what is referred to as a split bobbin transformer?

Screenshot 2025-05-30 195113.jpg

[tcaudle]

The way the circuit shows the original transformer wired in the schematic its a 28VAC Center Tapped transformer. While you get 28VAC on the outside legs its only 14VAC to center tap.(ground)
If the +12 power supply has a ground then its a full wave center taprectifier and the output is 14VDC (actually closer to 17-18VDC before the internal regulator), The replacement transformer can be made to be the exact same configuration by tying the 9 and 10 pins together and those to ground.

Easy to check : check from pin 7 to the 9-10 center tap and from pin 12 to 9-10 and both reads should be about 14VAC based on AC line voltage it can vary some but if there is the same voltage from 12 to 15 VAC on both legs to ground its good. I would find that +12 regulator and cheek the voltage (DC) out of that . Its more likely to be bad than the transformer.

[AREA]

Tom @ C&CNC for the WIN! Great info Tom.