20 Most Recent Miller Trailblazer 302 Welder Generator 907217 907216 - Page 8 Questions & Answers

What model and serial number?

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This is a very complicated machine and so I will say upfront that only a qualified tech should work on it. There are 2 fuses mounted on a tray holding PCB2. The tray is mounted on the lifting bail. The fuses need to be checked. Also there are circuit breakers and fuses mounted on the front panel that need to be checked. PCB2 is a control board monitoring the output and shuts down the weld power and aux power if there is an overload. The idle board is also watching the output and won't let the machine idle down if there is an overload. I have included the manual. Check Page 27 for overload protection and F1 and F2. An overload will occur if there is a shorted generator, shorted cube rectifiers, or shorted output diodes. Again, after checking F1 and F2, only a qualified tech should work on the machine. Good luc https://www.millerwelds.com/files/owners-manuals/O486H_MIL.pdf

the Trailblazer 302 diesel, has a fuel level sensor that tells Control PCB2 if there is fuel in the tank. PCB2 sends a signal to CR1, which lets voltage go to the Fuel Solenoid. If the sensor is bad, PCB2, CR1, or the fuel solenoid, fuel will not get to the engine. I am including the manual for the Trailblazer. Now keep in mind, the circuit may be a little bit different based on serial number. In the center of page 46 will be the fuel circuitry. Good luck https://www.millerwelds.com/files/owners-manuals/O217454U_MIL.pdf

Good eye. Yes that relay is CR1. It controls power to the main transformer, power to the feed motor, as well as providing a brake for the motor when the trigger is released. CR1 is controlled by the gun trigger. The contacts in CR1 will burn (the arcing you seen in the relay) and cause the problem you mentioned. The part number for the relay is #120706. All this is for the 70 amp model. The 90 amp model has a second relay with a small PC Board. It is a little bit more complicated and more could be the problem. I am enclosing the manual for the Cricket. It includes both the 70 amp and the 90 amp models. If you have the 90 amp model, the repair will be different and will require more advanced troubleshooting. Also. there are two other models for the cricket, the 200 and the XL, both having different parts. Now having said all, if you feel confident , the actual repair is not complicated but you have to understand there is a potential for shocking due to high voltage.. If you are going to do the repair yourself, make sure the welder is unplugged and that no one will be able to plug it in while you are working on it. You will have to check with a Miller distributor for pricing and availability. https://www.millerwelds.com/files/owners-manuals/O1307_MIL.pdf

Depending on serial number, Miller started out with Kohler manual start, Kohler electric start, and then Tecumseh electric start. They ended the series with a Tecumseh OH160, miller part #070732. I have included the manual. https://www.millerwelds.com/files/owners-manuals/O424E_MIL.pdf

Generally it all be on the faceplate on a sticker.

On your machine you have a fuel level sensor. I am including the manual. Check page 52 near the center of the page. The sensor plugs into PCB 2. You may have a loose connection there. https://www.millerwelds.com/files/owners-manuals/O4426AE_MIL.pdf

Which windings? And what is the serial number?

There are two major elements that could cause your problem. There is a bank of SCRs that could have one or two shorting. Also there is a main control board that tells each SCR how to work. This is a job for a factory repair center. They will be able to clean it out, do a visual check, and test the machine on a load bank. Do not try to repair yourself, high voltages exist and definitely a potential shock hazard.!! I have included a site that the owners manual. https://www.millerwelds.com/files/owners-manuals/O223BG_MIL.pdf

The serial number on an older 350D should be on the face plate either on a tag or punched in on the faceplate, sometimes near the bottom of faceplate. If there is no serial number there, you can call Miller with the engine type, engine serial number and they might be able to trace the machine number down. Other that, you can get a general span of number by matching up schematics with your machine. Manuals Parts

Here is the spec sheet for your welder. The only problem that I can see is maybe your power cord is too small. As you can see on the spec chart, the minimum the machine will draw at 115 volts is close to 20 amps. Now your have to multiply that by 1.5 for transformer surge. So now you are looking at 30 amps, which means you will need size 10 gauge wires in your extension cord. If you are going to do some heavier welding, you may even need to go to a #8 cables. What happens also, when you try to draw a lot of current, the generator will bog down, thus providing less power. It would be better if you could use 230 volts. https://www.millerwelds.com/pdf/spec_sheets/DC27-1.pdf

Here is a video to help you out. Good luck with that. https://www.youtube.com/watch?v=HzhafVQkqx0

Here is the manual for a miller machine. It may be close but it really depends on the serial number. Troubleshooting starts on page 22. There is a schematic on page 26. Check at the lower left for starter circuitry. https://www.millerwelds.com/files/owners-manuals/O411P_MIL.pdf

The potentiometer can be checked with a multimeter ohms range. Analogue is best. I would be surprised if the potentiometer is faulty but you might be lucky. MIG welders rarely use a pot to control the voltage - most often the voltage or power is adjusted in steps by one or more switches and it is the wire speed and current that uses a potentiometer.

I gather that you looked at the miller site for info on the machine? You were not clear about how it got hooked to over voltage though. If it was rewired to the pigtail and then disconnected and wired back to original? At any rate that machine can take 460 VAC so how did you arrive at the parts to replace or are you just throwing things in it till something sticks?

Check fuel pump and check carburetor bowl for stuck needle. If fuel was left in engine stuck needle or plugged jets. Confirm that choke is fully closing when cold. Hope this helps? Fuel Pump.

I am pretty sure there is such a machine as you say. So?

Usually, the drive motor voltage is derived from the weld voltage, so if you lose, the weld voltage, the motor will not turn. Feed some wire out in a setting that works, then switch to one that doesn't feed, and see if the wire will arc. If you have a voltmeter, check for DC voltage at the polarity changover. Might be a bad voltage range switch.

On a Bobcat, the big knob needs to be turned all the way up to 10. If it is, then the engine speed (RPM) might be too slow at fast speed.