Mig 251 boss wire feed board.

[Relic]

Mig 251 boss has a wire feeder pcb problem.
Has an RE191E circuit board.
Black wire is out of connector plug.
Think it should go to pin 9 of 10 pin connection plug.
This pin 9 goes to an input ofa quad opamp.
Black wire is one end of torch switch.
Anyone can help?
Source for pcb available online, but no machine information.

 

[eddie49]

I have searched for and found the RE191E PCB:

Toolex | Welder Mig Autoplus 250 C/Bd Control Circuit Board Re191E In Plastic Bag

www.toolex.com.au

and then done a Google image search for that picture, but not found a circuit diagram or any further information.
It looks like the board uses a "Half-Controlled Bridge", with two diodes and two thyristors to rectify the auxiliary AC supply and provide controlled DC for the wirespeed motor. The third thyristor is probably shorted across the motor to brake it. The small black relay will control the Contactor.

There will be the following five inputs and outputs:
- AC supply ( 24v AC ? )
- torch trigger
- Contactor
- wirefeed motor
- gas valve
At two wires for each, that means a 10-pin plug! I think you will have to cut cable ties and trace wires from the external components back to the PCB, then reverse-engineer enough of the track connections from the 10 pins to the components on the PCB to figure out how it all fits together.

 

[Relic]

Thanks for your enthusiasm.
Already done as you suggested.
48v ac on pins 1 and 10.
Motor on 2 and 3.
Gas and contactor off 5.
0 volts looping to these two further back in wiring.
4 not in use (pin goes to no track on pcb).
This leaves 6,7 and 9.
9 goes to a quad op amp input.
Most likely home for black wire.

Multi-layered pcb.
Hard to tell where 6 and 7 go to.
100 percent correct about scr,s
Tried 6 and 7 with black, no joy.
Looking at universal board from aliexpress with a 230-24v transformer.
Not sure wire feed motor is 24v?

 

[Relic]

Neglected to state other we from tourch switch goes to terminal 5 (from left to right).
Just desoldered LM324 op amp.
Going to fit a 14 pin ic socket for a new chip.
Will see if this works.

 

[Relic]

New chip did not fix.
Removed board and fitted cheap aliexpress board.
This came with a 28k ohm pot.
Found all wire speed on a very narrow band of adjustment.
A 10k ohm pot gave better span of control.

 

[Relic]

A board with adjustable burn back would be nice.
Stick out quite short with these boards.
Better than no welder.
1980s vintage WIA 180s in progress.
Have a other dinosaur type mig to look at soon on shop floor of similar age.

 

[Relic]

Of note.
Just fitted the same board to an elderly transmig 350.
Worked fine with wire clamp undone on dual rollers.
Sky fell in when wire clamped.
Motor turned slowly for a short period, then stopped working.
Stood back a bit and took stock of situation.
Propably the largest wire feed motor I have ever seen.
Suspect gearbox ratio not very low geared.
Suspect in-rush current has faulted 6 amp triac.
Inspection of fuse confirmed on the right track.
Fuse element is huge.
Motor label faded and unreadable.
Owner has a soft spot for this unit.
Motor to be inspected for brush or commutator problems.
Suspect retro fitting an after market dual rollers will not happen.
Load testing with wire clamped before continuing is a hard won lesson.

 

[Relic]

Revisited this problem.
Inspected wire feeder motor.
A bit of wear on commutator and brushes.
Still serviceable.
Found 32 volt 150 watts on gearbox.
Brake clean over haul.
Back to digging.
Found an issue with a melted fuse holder.
This was replaced.
Repaired board I had been using.
Board required 28v ac.
Fed it 32v ac.
Checked voltage at 100uf 50v cap.
45v there.
Real close to voltage limit so carried on anyway.
Fed the gas solinoid and contactor off the 24v ac supply. Through board relay contacts.
Hooked every thing up.
Works.
Adjusted coarse speed pot to as fast as it would go.
Adjusted fine speed pot down real low.
Think top speed is fast enough for 1.2mm wire.
1.6mm could be interesting.
32v motor on 24v better than no welder.
About to release unit into the wild.