XMT 350 prepower pc1 control board RC3 troubleshooting

[Gmoney44]

Did all the prepower check on xmt350 serial md4204 (except when igbt tester was needed, do not have one yet) all tests were within specs exept r1 &r8 bleed resistors on interconnect board pc2 reading about 34k threshold is 37-41. Assumed they were bad but when tested with everything unplugged it then reads within specs. Found that only when plug RC3 is connected the ohms drop out of specs, found that pins 1,2,5,6 on rc3 plug on interconnect board cause drops which ties into pc1 control board pins 4,5,6,7(common primary bus -, igbt gate drive signal and return).
Questions- I am assuming the only problem is on pc1 board? Is there a way to troubeshoot the more exact problem? If so and if someone knows the most likely issue can just that be replaced on the board?
Side notes- If possible I do not wish to replace the whole board if possible since they are are costly, I have someone who does board repairs but just need to point him in right direction of what needs to be repaired.
I have attached some picture of manual and if anymore need to be uploaded let me know. Thanks for any help!

[Bushytails]

I would figure that's close enough, and look for the problem elsewhere.

[jjohn76]

What is the problem with the machine?

[Gmoney44]

I have not plugged it in to run it yet. I was concerned I might do more damage.

[jjohn76]

I went back through my Tech Manual, which is older than yours. Mine says to remove all plugs before checking measurements, which I didn't see in the screenshots of the manual you show. Like Bushy said, it doesn't throw up any alarms, but it may be worth a call to Miller Tech to confirm.

[Gmoney44]

Yours says to do that for all prepowers checks? Mine says only on the pc1 tests.

[jjohn76]

My tech manual has a separate note in the PC1 and PC2 pre power checks to remove plugs before testing.

[Gmoney44]

Thanks jjohn and bushy. I am finally getting back to troubleshooting this machine. I decided to just power it up, Ive got a amp reading and will adjust on meter but Volts will spike initially then drop to .2. verified reading is correct with dmm. Checked supply voltage on hd1 and I have -10v (specs -15v) and 2v (specs 15v). according to manual its either the hall transducer or pc1 board? Is there a easy way to narrow down whether its the hall transducer vs the pc1 board? Would I be correct in thinking If i just unplug rc9 @ pc1 and I read spec voltage its the pc1 and if not its the hall device?

[Bushytails]

If you unplug the hall effect sensor and the voltages are still low, then it is not the problem.

You might be able to find the bad component by seeing if anything is getting hot. One of the two big heatsinks on the top board is going to be hot, and something else, somewhere, might also be hot. If you do this by poking things to see if they're hot, make sure the unit is unplugged and the capacitors verified discharged first.

[1997CST]

What's your OCV?

[Gmoney44]

Not sure if i did this right but I unplugged c9 and got 0 reading on harness end of hall sensor and same 2v and -10 readings on the board pins.

I do not have ocv engaged on the board but if that doesn't matter for what your thinking 1997cst, how exactly do I get a reading the ocv, I'm not seeing it in my manual.

[Gmoney44]

Also when I do engaged the ocv on board I show 14v on display. And 14v and -5v on hall

[ccawgc]

From command ground the 4 wire to the lem should read +15 and -15 and 0 and 0 the minus might read -14.4.
If different unplug lem and retest pc1 supply to LEM if voltage jumps up Lem is bad. if it stays low then pc1 is damaged. might also
have something else pulling the voltage down. if only the LEM is bad you should get output with LEM unplugged. OCV. current will go to max if you try to weld.
Also check feed back wires where they connect to the weld terminals.

[Gmoney44]

Lem?

[jjohn76]

Hd1 = lem