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**ryanjones2150** · 03-07-2016, 06:40 AM

Man, that looks like a lot of work you did there. I'll be of no help unless you need your machine hit with a hammer. There are certainly some folks here that understand what all you wrote and should be able to help. Good luck.

**griff01** · 03-07-2016, 07:12 AM

Originally posted by Mustang51 View Post

Hi. I recently purchased a used Millermatic 350 that has issues. It is incapable of striking an Arc. The actual output voltage measured on either the output terminals or on the wire feeding out of the gun to the ground clamp matches the voltage selected on the display, in my case I tested at 21.0vdc however if the wire touches ground it immediately drops to 0-0.2vdc (My understanding is that the voltage should be much higher than displayed until an arc is struck and then should match the display).
I downloaded a technical manual and have performed the pre-powerup tests, these are my results. Testing done with a Fluke 789 process meter

Output Diode Check:

meter neg to output pos, meter pos to output neg: 1.014kohms
meter pos to output pos, meter neg to output neg: Shifts between OL and 2.67kohms
(I find it odd that meter polarity in the ohm position changed results)

D1:

Forward bias (meter in diode test mode): (Upper Diode) 0.170vdc
(Lower Diode) 0.170vdc
Reverse bias (meter in diode test mode): (Upper Diode) OL
(Lower Diode) OL
Forward bias (meter in ohm mode): (Upper Diode) 5.43kohms
(Lower Diode) 5.41kohms
Reverse bias (meter in ohm mode): (Upper Diode) Shifts between OL and 9.2kohms
(Lower Diode) Shifts between OL and 9.2kohms

D2:

Forward bias (meter in diode test mode): (Upper Diode) 0.168vdc
(Lower Diode) 0.168vdc
Reverse bias (meter in diode test mode): (Upper Diode) OL
(Lower Diode) OL
Forward bias (meter in ohm mode): (Upper Diode) 5.32kohms
(Lower Diode) 5.34kohms
Reverse bias (meter in ohm mode): (Upper Diode) Shifts between OL and 9.0kohms
(Lower Diode) Shifts between OL and 9.0kohms

Input Rectifier Check:

(3) to (L1-1) Forward bias (diode test) 0.422vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.22Mohms Revrese bias (ohm mode) 4.22Mohms

(4) to (L1-1) Forward bias (diode test) 0.421vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.20Mohms Revrese bias (ohm mode) 4.20Mohms

(5) to (L1-1) Forward bias (diode test) 0.418vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.18Mohms Revrese bias (ohm mode) 4.40Mohms

(3) to (C1 (PM1) ) Forward bias (diode test) 0.418vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.17Mohms Revrese bias (ohm mode) 4.18Mohms

(4) to (C1 (PM1) ) Forward bias (diode test) 0.419vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.16Mohms Revrese bias (ohm mode) 4.17Mohms

(5) to (C1 (PM1) ) Forward bias (diode test) 0.419vdc Reverse bias (diode test) OL
Forward bias (ohm mode) 4.39Mohms Revrese bias (ohm mode) 4.16Mohms

Capactitor Check:

C3: Starts around 290kohms, climbs to around 3900kohms, then quickly stabalizes to 1.02Mohms
C4: Starts around 290kohms, climbs to around 3900kohms, then quickly stabalizes to 1.02Mohms

Resistor Check:

R11: 41.8ohms R12: 42.4ohms

PC2 Diode Check:

D1:

Forward bias (meter in diode test mode): 0.327vdc
Reverse bias (meter in diode test mode): 0.433vdc
Forward bias (meter in ohm mode): 1.984kohms
Reverse bias (meter in ohm mode): 1.984kohms

D2:

Forward bias (meter in diode test mode): 0.326vdc
Reverse bias (meter in diode test mode): 0.433vdc
Forward bias (meter in ohm mode): 1.984kohms
Reverse bias (meter in ohm mode): 1.984kohms

IGBT Check:

PM1:

C1 to E1: 77.1kohms
C2 to E2: 77.1kohms
E1 to PLG5(10): OL
E2 to PLG5(7): OL

PM2:

C1 to E1: 77.1kohms
C2 to E2: 77.1kohms
E1 to PLG5(6): 99.8kohms
E2 to PLG5(9): 99.8kohms

The conclusion I have drawn from these tests are that both diodes (D1 and D2) on the PC2 board are failed and IGBT PM1 is also failed. I'm looking for some thoughts and advice from anyone with some experience about my conclusions and if this seems plausible as the cause of my issues before I source replacement parts.

Thanks

You may as well go ahead and post your serial number. You are not likely to get any help without doing so,

Griff

**Miller Kevin** · 03-07-2016, 08:59 AM

Mustang,

I would agree with your diagnosis.

Kevin

**Mustang51** · 03-07-2016, 01:35 PM

Serial number is LG111067B

**Mustang51** · 03-09-2016, 09:27 AM

So looking for places to order parts from, seems like miller4less has the best prices unless I buy used off of ebay. Anyone know of any better place if I'm looking for new?

**Mustang51** · 08-08-2016, 06:15 PM

As a follow up to this post, I wish I would have investigated just a little bit more before ordering another PC2 board which was not cheap. I had wanted to leave it connected before getting another one so it would be easy to reference the connections when installing another board. As it turns out it was all being caused by an unplugged connection to IGBT PM1 that I did not see until removed I the board. At any rate I'm happy to have a working machine.

**ryanjones2150** · 08-08-2016, 08:51 PM

...AND a spare PC2 board!

**Aeronca41** · 08-08-2016, 09:52 PM

Don't feel too bad (other than your wallet!). Frustrating but very common; we all do stuff like that. At least it's working. At my age, I'm finally learning to look, gently prod, and otherwise physically search for the trouble for longer than ever seemed reasonable when I was doing electronics repair in my younger and more impetuous days. Amazing how many things you can fix that way without ever reaching for the meter or scope.

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Millermatic 350, technical advice needed

Millermatic 350, technical advice needed

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