Miller 330 A/BP - DCEP (Reverse Polarity) No Output

Brettroberts321 · Tue Dec 22, 2020 9:27 am

Hello All -

Noob here, working on getting a miller 330 A/BP up and running (bought it in an auction for $60). Got it home, cleaned off connections, wired it up and plugged it in. Nothing kicked on. Did some troubleshooting and replaced the F2 fuse per the manual, and bam, machine and fan kicked on.

My first thought before I dive into the TIG journey is to make sure the sticking welding functionality is working properly. I bought a new stinger and ground clamp and hooked it all up. Odd thing is that when I put it in DCEP (Reverse Polarity), no welding output (testing with E6013 1/8" electrode, in the 20-250 range). Put it in, DCEN (Straight Polarity) and bang was immediately able to strike an arc. Talked to a friend and he told me to use a multi meter to test the output on the "Work" and "Electrode" studs. When testing the studs in DCEN, I was getting around 20.2 volts across. For DCEP, I was only getting .015 volts.

My question then brings me to, where do I go next test why the DCEP is not working? Looking at the functional diagram (page 12), would I need to be testing the Main Rectifier (SR1)? I see that on OM-340 Page 4, it lists the diodes and caps for the rectifier that could be troubleshooted? Should I be testing/cleaning the Contact Board, switch - polarity (S10)? I am having fun with this journey and learning the process of electrical troubleshooting so sorry if any of these are super basic questions haha. Any help is much appreciated.

Here is the manual I am working off of:
https://www.millerwelds.com/files/owner ... 0H_MIL.pdf

Brettroberts321 · Mon Feb 01, 2021 9:25 am

Following up on my post:

Cleaning the points on the contact board, switch - polarity (S10) did the job. I cleaned the points with a wire wheel/sprayed them with electrical parts cleaner. I am now getting output on both DCEP and DCEN. Now on to getting it set up for TIG/AC welding!

BugHunter · Mon Feb 01, 2021 5:10 pm

Good Job!

I'm surprised nobody saw this and commented. I wouldn't have been any help either way.

Welcome to the forum!

MinnesotaDave · Tue Feb 02, 2021 4:14 pm

On those machines (and ones with similar contacts like my Bobcat 225nt) it's a good practice to move through the contacts every time you use it.

It's even in my Bobcat manual to do that. Keeps them from getting corroded I suppose.

G-ManBart · Fri Feb 05, 2021 2:28 am

I never saw the original post, but glad you got it working!

The HF start isn't the most robust on the 330 A/BP, but the arc is very smooth...great machine to learn on. Not only that, but you stole it at that price!

Brettroberts321 · Thu Feb 18, 2021 11:14 am

MinnesotaDave wrote:On those machines (and ones with similar contacts like my Bobcat 225nt) it's a good practice to move through the contacts every time you use it.

It's even in my Bobcat manual to do that. Keeps them from getting corroded I suppose.

So before I went out and started buying all the TIG equipment, I was testing AC voltage and I am getting no output at the studs. Getting good voltage for Straight and Reverse polarity, but going to take another look at the contacts for AC and see what is going on.

Brettroberts321 · Thu Feb 18, 2021 11:15 am

G-ManBart wrote:I never saw the original post, but glad you got it working!

The HF start isn't the most robust on the 330 A/BP, but the arc is very smooth...great machine to learn on. Not only that, but you stole it at that price!

Thanks, definitely has been a learning process putting it back together and understanding the machine!