Circuit board for my Miller

Hello Doug, can you use a soldering iron? Can you use a multimeter? If yes, how about having a crack at getting your machine up and running again?

There are a lot of helpfull people on this group, with a combined group effort we could probably help you fix that unit of yours. Is this the hook up diagram? page 24.

If you are interested in having a go at fixing the board can you take a photo of it so we can all see it.

How do you know the board is the cause of the trouble? Are you just guessing? Have you substituted a known good board for yours and proved it is dud for sure? Sorry I had to ask.

Over to you Doug,

Regards, John Crighton Sydney

Parts pricing is set by Miller. Unfortunately replacement boards are always a bit pricey.

I agree with John. How did you determine that the board is bad? I had a problem with my 185 and it was in the switch wiring in the gun.

The board regulates dc voltage to the drive motor. Are you sure the motor is good? If it is the board, do you know why it failed?

The circuit is pretty simple and is repairable.

Regards, Tom

Hello Tom, with you having the same machine as Doug and maybe Brad, with his connections in the trade, can get a copy of the circuit diagram of the control board, fault finding could now be pretty easy. Is there any chance of a circuit diagram from you Brad?

Just for interest Tom, can you remember what is on that board? Don't go opening up your machine just yet. Doug may not come back.

Where are you Doug? You have got me interested.

Regards, John Crighton Sydney

I'm sorry about the slow response, but I'm usually busy with other things on the weekends and of course I have to work on Monday.

Now to fill you in on like Paul Harvey would say "The rest of the story" A couple of weeks ago we got a lightning strike close to the house and barn, knocked my cordless phone off the charger and blew the modem in the computer (yes I have a surge protector on it), also took out two breakers in the shop. The first time I went to use the wire welder the wire runs out at what seems like a speed faster than the fastest setting. So going through the electrical diagram they just show the connector going to the circuit board. I checked the resistance through the pot. for the speed control and it checked out alright. The motor and gun switch works, because it obviously feeds too fast. I popped the circuit board out and found two blown capacitors, and maybe a third one. I went to the local Radio Shack and the guy in there was of very little help. He told me I would need to know the value of the old ones so he could give me a replacement. Unfortunately with the old ones being burnt out I can't get a value.

I took a picture of the board, I don't know how well you will be able to see it, but it is capacitor C5, C9, & C10 that are in question. The C9 capacitor has the top blown right off of it and the C5 is blown out the side, the C10 looks as though it got hot so I was going to replace it too.

Now we're getting somewhere. Can you post a link to a web site where the photo is? Or email it to me. You may have some other parts that are failed. I know that they feed 24 volts ac to the board and it is rectified to dc. If one or more of the diodes shorted, that would place ac on the caps. It could explane the burned caps.

tmiller(at)umaryland.edu

If necessary, I could look at the board in my 185. Let's see if someone else comes up with a schematic.

Tom

Hello Doug, thanks for the e-mailed picture. I will talk to you on the group..

Tom can help you out here with the value of the capacitors. You will probably have to wait until he gets some time at the week end also. In the mean time, buy some solder wick and maybe one of those tools called a "solder pullit" and remove the known dud capacitors. Get your self into a mind set: say to yourself, "I am going to fix this board. I am not going to pay $226. I will check every single component if I have to."

Start with the easy stuff. Lift one end of the resistors and check each one with the ohm meter range of your multimeter. Do the same with the diodes. Get rough if you like and snip the component lead and blob it with solder later. Don't struggle to remove a component that costs next to nothing and end up mangling the tracks. Protect the tracks before cheap parts. Cheap stuff can be replaced later when it is working. Lets just find the duds for now.

Remove the transistors and check them also with your ohm meter. I like to use an analogue type multimeter with a pointer not a digital ohm meter for checking the transistors junctions.

The remaining capacitors, remove them also and check them for leakage. Digital multimeters are becoming so cheap these days, some even have a capacitor measuring function. See if you can borrow a multimeter that checks capacitors also. If you can't get one of these capacitor checking DMMs, then just reverse the leads of your analogue ohm meter when testing the capacitors for leakage and you will see a small meter movement as the capacitor charges.

If there are a few welding stores near you, call in and ask for the diagram for the board. You never know your luck, some will tell you to bugger off and others may give you a copy. Ask to speak to the repair man if possible not the boss or counter attendant. A technical guy is more likely to help you.

Have a go Doug and have some fun,

Regards, John Crighton Sydney

Oh well I guess I will have to shell out $226 for a new one, because of the lack of responses back and I really need the welder.

Hey Doug, what do you mean lack of responses? We have been waiting to hear from you.

We are all here ready to help you fix the board, where have you been?

Tom has the same millermatic 185 mig welder. Did you not see his post offering to look up the value of the damaged capacitors on your control board?

How did you go doing individual component checks on the board? Did you find any dud semiconductors?

Over to you.

Regards John Crighton Sydney

I guess maybe I have not keep up with everything, but I did not see his post. I been watching for a reply but did not see one. Anyway I know I need three capacitors, I really don't want to unsolder everything off the board just to check the resistance. If there is anyone that would be willing to do this for me? I would something for the time and effort. I am thinking of getting a new one and repairing this one in case this would happen again. These things always seem to happen when you need it the most. Thanks for your reply I wish I could find Tom's but I don't see it.

Doug, here is a copy of Tom's post

---------------------------------------------------------------------------------- Now we're getting somewhere. Can you post a link to a web site where the photo is? Or email it to me. You may have some other parts that are failed. I know that they feed 24 volts ac to the board and it is rectified to dc. If one or more of the diodes shorted, that would place ac on the caps. It could explane the burned caps.

tmiller(at)umaryland.edu

If necessary, I could look at the board in my 185. Let's see if someone else comes up with a schematic.

Tom

------------------------------------------------------------------------------------------

Doug, have you been to any welder repair shops and asked for a copy of the schematic? If they don't want to give you a copy then plead your case and ask for the values of the destroyed capacitors. They should at least do that.

Write to Miller's managing director for the values of the capacitors if necessary, if their after sales service people will not help you out with the values or a schematic.

Tom is here and willing to help you with the values, send him the picture and the reference numbers if you have no luck with Miller or their repair agents.

If you get lucky with a schematic with component values and the welder repair people only wish to do board replacement repairs and not do component level repairs, you could take your welder to your local TV repair shop or a Ham radio electronics man and they might be willing to fix it for you. With a circuit diagram any electronics man will be able to fix the board. This $226 replacement board type of repair is totally wrong. I wonder if someone has a service exchange type of business. You give them your dud board and for $50 or so you get a used but repaired board in return.

Getting back to the dud board. At the moment it is dud and worthless so what have you got to loose by ripping into it. Nothing. OK you don't like the idea of carefully removing every component for checking, perhaps you don't have the skills. So cut tracks to isolate components for checking. Use a sharp stanley knife/box cutter. Make one neat little cut, a tiny nick, to isolate a resistor, capacitor or diode. Make two track cuts to isolate a three legged transistor. The cut tracks can be made good by soldering a little fine strand of wire across the narrow cut.

Get yourself in the right frame of mind, sit down at the kitchen table with desk lamp, magnifying glass, multimeter, modelling knife/box cutter and get started. Two to three hours and its done. Once you find the dud parts we can then start looking for suitable replacements.

Hoe into it Doug, you can do it. You have nothing to loose and everything to gain.

Regards, John Crighton Sydney

I sent you an email. I will try to help you get this working. I have a working 185 to compare it to and most of the parts on the board. As long as the board track is good and the board is in tact, it should be repairable.

Tom

Contact Innovat. They rebuild circuit boards for most welders and industrial equipment. Call 276-783-9771, at least this is the last # I have for them.They are in Marion, VA. Rebuilds are typically 1/3 the cost of new.

Good Luck

brad