Miller Trailblazer 302 idle only / meters not displaying

[sduncan9]

Hello! A new to me 302 with a Kohler engine. S/N MA150366H, has a couple of issues, firstly it will not idle up when the switch is turned to the run position, it stays at a low idle. The engine runs fine, if I pull the ground wire off the idle solenoid the engine runs at a high idle fine, there is a steady voltage to the coil whichever switch position.

Secondly the meters are not displaying anything. I am starting to trace wiring and check voltages but haven't had that Ah ha! moment yet. Any thoughts?

I did some different searching here and now believe this may be a result someone jumping or boosting the welder. I did learn that the gentleman who dropped it off had boosted a dead battery and replaced the F6 (?) fuse by the starter. So far I have not found anything obviously "blown" on PC1 and the voltages seem to be testing okay so far, but according to what I have read now, this explanation makes sense. It would be nice to see something obvious, but as with other electronics it's not always that obvious to the naked eye. Only the two center red LED's on PC2 are on, the meters or fuel gauge do not light up, and the low idle solenoid remains energized with no change when ignition switch is changed from idle to run....

Edit: After describing symptoms to Miller Tech Support, it was suggested to replace PC1 as it was likely the culprit. Further testing can be done after replacing that board. It would be nice to see something fail on the board or have a test that said hey the problem is here...

Thank you for any suggestions...

[ccawgc]

talked to one of my engine guys and he said be prepared to replace both pcbs. control display and power pcb.
jump starting these welders will blow both pcbs out.

[duaneb55]

What ccawgc said.

Have seen one, the other or both boards damaged from jump starting. The last TB302 I saw had both boards damaged with the control board failure causing the power board failure. Most board repair shops consider the main control board non-repairable due to it being a tri-level design where there are circuit traces "sandwiched" between two boards making soldering replacement components to the center layer very difficult. Not necessarily impossible but likely not easy.

[sduncan9]

Good afternoon CCAWGC and duaneb55.

Thank you for your input. I also had spoken with a Miller Tech and he said to start with replacing the PC1 board first, so that is what has been ordered (about $1100CAN).. I asked specifically if there was any way to know if one or both boards would need replacing and he said to replace the one first and only then would I be able to tell if the second was required. When you mention the main board taking out the power board, that makes me a little nervous about just changing the power board....

About the main board repair, that is the same information I received when I inquired locally.

The power board LED is on, and the test points I checked (not all) were close to what they should be, but as it is stuck on idle, and I believe that is on the power board, maybe that is the place to start.

In any case, thank you for your input.

Regards,

Stuart

[duaneb55]

Yes, idler control is on the power board and as such is likely faulty. Very risky just changing expensive parts though.

I've had both repaired by a local former NASA satellite technician who was able to figure out the board logic within less than 5 minutes of reviewing the drawings. One must know how something works before they can troubleshoot and finally repair something. He even knew WHY the failure on the control board caused the power board failure.

That power board BTW was previously repaired to the tune of $200+ by a well known shop who told me after the fact they couldn't test the control board. That repair lasted about 20 seconds.

[Meltedmetal]

Duane55,
Did you happen to inquire if the tech could explain or offer a theory as to why boosting these machines takes out the circuit boards? The evidence says it does but I am curious as to how.

---Meltedmetal

[sduncan9]

Yes, idler control is on the power board and as such is likely faulty. Very risky just changing expensive parts though.

I've had both repaired by a local former NASA satellite technician who was able to figure out the board logic within less than 5 minutes of reviewing the drawings. One must know how something works before they can troubleshoot and finally repair something. He even knew WHY the failure on the control board caused the power board failure.

That power board BTW was previously repaired to the tune of $200+ by a well known shop who told me after the fact they couldn't test the control board. That repair lasted about 20 seconds.

Duaneb55, thank you for sharing your experience. I always prefer to know what the problem is prior to replacing parts, expensive or not. With electronics, I know enough to be dangerous and hence defer to the experts for guidance, as in this case calling Miller Tech support. While I asked if both boards should be changed he said just replace PC1 first, so I am following his direction. He did not explain why this happens, just that it does if they are boosted / jump started...

[duaneb55]

I'm not sure anyone knows exactly why jump/boost starting takes out one or both boards or at least I've never heard anyone claim to. What I do know is there have been an untold number of cases of one, the other or both boards going out when a unit was jumped/boosted which makes it even more of a mystery. From my experience changing the power board first might result in a second failure IF a failure on the control board caused the original power board failure. That is likely why the Miller tech said to change the control board first and I would think they may know more about the matter than anyone else at this point. I just don't like troubleshooting by changing expensive parts that I or another owner has to pay for first. Might not be such a big deal for a Miller service facility.

[sduncan9]

I'm not sure anyone knows exactly why jump/boost starting takes out one or both boards or at least I've never heard anyone claim to. What I do know is there have been an untold number of cases of one, the other or both boards going out when a unit was jumped/boosted which makes it even more of a mystery. From my experience changing the power board first might result in a second failure IF a failure on the control board caused the original power board failure. That is likely why the Miller tech said to change the control board first and I would think they may know more about the matter than anyone else at this point. I just don't like troubleshooting by changing expensive parts that I or another owner has to pay for first. Might not be such a big deal for a Miller service facility.

Actually Duaneb55, the first Miller tech said to change PC1 (the POWER) board first and then check the PC2 (Meter / Main board). After emailing Miller tech, this time I was told to check battery voltage exists on RC21 pin 3, if battery voltage is there (SW2 on) change PC1, if no voltage change both boards. My result is no voltage so I guess I will try to order the second board. And yes I haven't got a straight answer to what exactly is happening, but it seems to be a known problem. Thanks again for following along. I will post the outcome in case it can help someone else in the future.. Cheers!

[Meltedmetal]

Thanks for the responses. I don't question that it happens. I guess maybe one would have some clues to track it down if they had the board diagrams and knew which parts are the parts that fail. Am I correct that it is only the Trailblazer series that is susceptible to this and not all Miller engine drives?
All I can think of is that it must be some strange current flow caused by the inrush current into the dead battery maybe by not connecting the ground battery to battery. Even if I had one I don't think I'd test out that theory though. It is a mystery.
---Meltedmetal

[Kpack]

Would you be able to jump one from a battery of a vehicle with out the vehicle running ?

[sduncan9]

Thanks for the responses. I don't question that it happens. I guess maybe one would have some clues to track it down if they had the board diagrams and knew which parts are the parts that fail. Am I correct that it is only the Trailblazer series that is susceptible to this and not all Miller engine drives?
All I can think of is that it must be some strange current flow caused by the inrush current into the dead battery maybe by not connecting the ground battery to battery. Even if I had one I don't think I'd test out that theory though. It is a mystery.
---Meltedmetal

Good morning Meltedmetal,

I was in contact with Miller Tech support again this morning and possibly received some clarification on the board failures. His explanation was that with poor battery connections or a dead battery that is not working properly (not acting as a buffer) that when stopping cranking the engine the residual magnetism can induce a very brief but high voltage spike back into the electronics of the system which may damage one or more of the boards. In a good operating system this shouldn't happen, but I think if this is the case a warning not to jump start the welders would be a prudent thing.

In this case the absence of battery voltage between pins 3 and 5 of RC21 (on PC1 with SW2 ON) indicates that there is damage to PC2 as well. In his opinion replacing PC1 alone would likely result in an immediate failure so he recommends replacing both PC1 and PC2. I now have both boards on order (about $2300 CAN).

At this point I have not seen any obvious component failures on the boards but will look closer after they are replaced. As I understand it PC2 is a multilayered board so damage to the center traces may not be visible and may be hard to repair.

Thank you for being involved!

[sduncan9]

Would you be able to jump one from a battery of a vehicle with out the vehicle running ?

From what I have been told and read, I believe it would be best to charge the battery without trying to start it and the safest thing would be to recharge the battery with the cables disconnected. Having said that if there was ever any question, replace the battery, that expense would be a lot easier to handle than the two boards. Also, check the voltage output when charging to make sure there has been no damage to the voltage regulator that may cause problems.

Having said that in the real world, I know I have jumped welders more often than I should apparently. An expensive lesson learned....

[Meltedmetal]

Good morning Meltedmetal,

I was in contact with Miller Tech support again this morning and possibly received some clarification on the board failures. His explanation was that with poor battery connections or a dead battery that is not working properly (not acting as a buffer) that when stopping cranking the engine the residual magnetism can induce a very brief but high voltage spike back into the electronics of the system which may damage one or more of the boards. In a good operating system this shouldn't happen, but I think if this is the case a warning not to jump start the welders would be a prudent thing.

In this case the absence of battery voltage between pins 3 and 5 of RC21 (on PC1 with SW2 ON) indicates that there is damage to PC2 as well. In his opinion replacing PC1 alone would likely result in an immediate failure so he recommends replacing both PC1 and PC2. I now have both boards on order (about $2300 CAN).

At this point I have not seen any obvious component failures on the boards but will look closer after they are replaced. As I understand it PC2 is a multilayered board so damage to the center traces may not be visible and may be hard to repair.

Thank you for being involved!

Thanks for the update. I wouldn't have thought it would be extremely difficult/expensive to protect those boards from voltage spikes but I'm not an electronic engineer.
$2300 CAD , ouch, ouch. Hope you get it purrrrring soon.
---Meltedmetal

[duaneb55]

No doubt it's a voltage spike that is the evil culprit and what you relayed of what the Miller tech said makes perfect sense. I didn't bother to dig into it but I've read in later manuals not to jump start but rather remove/disconnect the battery to charge it. I suspect this is to remove the temptation to crank it and avoid damage from a booster charger.

I'd say there's a 99.999999999% chance the unit will work just fine with both new boards.