1995 miller 225g voltage problem

[RODBUSTER]

Hi, this my first post hopefully in the right forum. Anyway I have 95 225g plus with 937 hrs, every thing works fine except for the constant voltage,when selected it puts out about 42 volts and will not adjust lower with the fine adjust. And when in the cc mode the current adjusts as it should. Also just incase its related the idle soleniod doesn't work unless i work the ignition switch back and forth fron run to idle. I'd appreciate any input anyone may have, THANKS,"RODBUSTER"

[ccawgc]

You in the right place, but I need the full model name and serial number,
Trailblazer, bobcat, blue star ect. With out it I can't look up the service manual and diagrams.
The Idle problem could be the Idle timer. Depending on age and model it can be on the main pcb or a smaller module. 42 volts sounds good for OCV. Look at the diagram on you cover and look for feed back wires that are sending weld voltage back to the control pcb.
Make sure they are connected.

[RODBUSTER]

Thanks for the reply, The full name is bobcat 225g plus, s/n#kf875070,
THANKS "RODBUSTER"

[duaneb55]

Your CV open circuit voltage (OCV) is definitely too high at 42 volts. Should be a maximum of 33 volts.

Does it increase from 42 volts?

When you say the CC settings adjust correctly, do you mean you can increase/decrease the output within each range with the Fine Current control or just with the Current Range selector?

Has someone been working on the unit recently?

[RODBUSTER]

Hi, duaneb55, The answer is yes, I did some welding with it today, And did some testing, At the highest it is 50-52 volts and lowest 40-42, And yes Fine control works corectly in cc, As far as being worked on I don't know I've owned this machine for about 3 months and this is the last kink to work out, I've opened it up to inspect but nothing was touched by me

[duaneb55]

OK, that's about the correct voltage differential. Just too high.

What is the OCV in CC/DC and CC/AC? Should be 72 and 80 respectively.

It could be the tap strap position on trim resistor R2 is incorrect or one of the two circuit wires is on the wrong end terminal. If the CC OCVs are high, that will be the place to look.

[RODBUSTER]

Alright, The cc/dc is 95-108 and the cc/ac is 64-74. I will check the terminals when I get home this evening, I appreciate the help, electronics are not my strength,

[duaneb55]

Interesting. AC is actually low and DC is way high same as CV mode. Should have seen AC higher than DC in CC. I'm still thinking trim resistor tap location and/or circuit wire position.

Let us know what you find and if you need help on the wiring diagram just give a shout.

In case you were wondering, this is what R2 looks like:

[RODBUSTER]

Thanks for the picture,I adjusted the tap location out and it lowered the voltage very little
cv 39-49 cc/dc 92-106, I'm not sure where I'm going from this point:

[duaneb55]

Your targets are:
CV - 33VDC
CC/DC - 72VDC
CC/AC - 80VAC

Move the tap away from the end terminal that has the other wire connected to until OCV is within spec.

Note the typical relationship between the tap and end terminal with the other wire in the previous photo. If the other wire is attached to the end terminal closer to the tap, OCV will be higher than specification.

[RODBUSTER]

I moved the tap as far away from the other terminal as possible and cv was 39-49 and cc/dc 92-106 ,I also moved it the other way just to make sure and the voltages just went higher

[duaneb55]

OK. Let me think on this a bit.

[duaneb55]

What is the AC voltage at the auxiliary power outlets??

Locate SR2 and check AC input voltage at wires #22 & #29 or at 4-pin plug PLG6 pins #3 & #4. If you're not sure as to what you're looking for, let me know and I'll post a couple photos.

[RODBUSTER]

Pictures would be great, I'll do some testing tomorrow, THANKS ALOT

[duaneb55]

PLG6/RC6 looks like this with pins #3 & #4 on the right side of the connectors. Pins #1 & #2 run down to the rotor brushes.


Bridge rectifier SR2 is down in here behind all the wires . . .


. . . and looks similar to this.

[RODBUSTER]

Ok, Auxilary power outlets are at 125v ac, And SR2 reads 24v, And somthing else interesting happened today when I removed the the top cover on the machine before I started it, I couldn't power anywhere, and when I replaced it I had power again could this be a ground problem? Also the auxilary power outlets adjust with the fine adjust control from 105-125 ?????

[duaneb55]

I expected - rather hoped - auxiliary power would be higher to support my suspicions but that doesn't pan out with only 125V.

Was SR2 reading at low idle or weld/power speed? Sorry I didn't specify but it's low either way.

I'll be honest, nothing is adding up here. Are the batteries good in your VOM?


. . . and now the top cover thing. Definitely check the #33 ground wires between the front panel and chassis frame.




Oh, and the change in auxiliary output voltage when you adjust the Fine Current control is completely normal.