Miller MIG Welder NOOB Repair Question

[frostheave]

Hi All, hope this isn't too dumb a question.  I'm a noob at troubleshooting and am looking for some confirmation.

I have a Miller 350P Aluminum MIG welder with no output to the external push pull gun motor.  I found that the negative lead of the motor connects to RC14 Pin6 which connects to Q24 in the attached picture.  Does the damage visible to Q24 look like it has caused it to fail?

I will be contacting Miller Welding tomorrow to see if I can purchase a schematic, or at least a part number for Q24.  Am I headed down the right road?

[p.larner]

that q4 looks toasted,no numbers tho,good luck,maybe remove it and test tho with a cheapo chineese component tester?.

[frostheave]

Thanks p.larner.  I agree, Q24 looks bad.

I got a hold of Miller and the part is a Fairchild FDD3682 N-Channel MOSFET.  Cheap, 10 for 10$ USD.  They are on the way.

Now I'll brush up on my troubleshooting skills and see if I can test the remaining MOSFETS in circuit.  Also, I need to find out the recommended way of removing conformal coating before desoldering/soldering.

[KG7AMV]

My Experience with miller is if you call tech support and ask nicely and know know what you are doing and you have machine serial #, Board # and revision # if it is out of warranty and or production revision they will generally give schematic and bom.  Miller has always supported the self/independent repair of their machines.

[frostheave]

Very good.  I will ask again tomorrow.  Thanks.

[frostheave]

So, just to complete this thread.  By the way, I was able to compare readings between
the failed board and a known good PC-1 board.  That was a big help.

* 350P Aluminum Welder had HELP 6 code and push pull gun motor did not turn
* Replaced Q23 and Q24 on board PC-1
* HELP 6 code cleared but gun motor still did not run
* Replaced D5, D6, and R264 on board PC-1
* Welder now works as normal

Q23 and Q24 are FDD3682 Mosfets
D5 and D6 are P6SMB15A-E3/52 Diodes
R264 is a LRC-LR2512LF-01-R200-F Resistor

[KG7AMV]

Thanks p.larner.  I agree, Q24 looks bad.

I got a hold of Miller and the part is a Fairchild FDD3682 N-Channel MOSFET.  Cheap, 10 for 10$ USD.  They are on the way.

Now I'll brush up on my troubleshooting skills and see if I can test the remaining MOSFETS in circuit.  Also, I need to find out the recommended way of removing conformal coating before desoldering/soldering.

Miller has been great at supporting #righttorepair providing schematics and component level information.

I am Glad you were able to fix it.