Capacitor Filter PCB Repair

[DD-YATES]

I was welding one day last summer with the Powcon 300ST. I think I was pushing it too hard when I was making some stands welding with 5/32 8010's, and suddenly I turned and looked, didn't hear a noise or nothing and black smoke was billowing out the backside of the 300ST, I quickly unplugged it. After much crying in my beer that night, the next day I took the cover off and found what the manual identifies as a Capacitor Filter PCB board with three small capacitors , three varistors, and six diodes and a few resistors. It has a part # of 100199-001 in the manual and printed on the board.




Everyone knows you cannot just run out and buy another board. So I would like to attempt to repair the board myself if I can get the right values for the damaged components on the board and get those components from a electronic supply house. I know nothing about electronic repair. I know I will need the right tools for the job though. I have nothing to lose if I screw up.

1. So has anyone ever repaired their own boards before and therefore has the knowledge and experience they could share, what tools are needed?

2. The only components with visible damage are the three capacitors. Does anyone have a Powcon with those values readable they could give me? (The 100199-001 board is the same on 300SM, 300SS, and several others I downloaded the manuals for.)

3. Can anyone with experience tell me how to test a varistor, a diode and resistors. These dont have visible damage but may still be damaged. All I have is regular VOM meters. Do I need something else to test with?

Anyone with electrical knowledge would be greatly appreciated.

[ArcPowTech]

First of all, if you can manage to remove the remaining parts of the capacitors, the unit should still run without them. They are intended for voltage spike protection and, to a lesser extent, phase balancing. Running the machine without them does pose the risk of a voltage spike getting further into the machine and, worst case scenario, causing an SCR to fail. But you can at least run it long enough to see if there are any other issues with the machine.

Second, a replacement board actually is available from Mirabel Industrial Welding Equipment. They manufacture the Workhorse welders that were previously made by Arcon Welding, which are extremely similar to PowCons. You can contact Mike at mike@mirabeliwe.com

You can certainly try repairing the board. Some of the traces are fairly large, so you'll need a fairly high wattage soldering iron with a somewhat beefy tip. The capacitors themselves are usually 600nF or 680nF but what is special about them is they are X2 Safety-certified capacitors. You can get them from Mirabel as well.

As for testing the other components, a good first step is to check the resistance. The diodes should have fairly low resistance in one direction, and nearly infinite resistance in the other direction (if it's low resistance both directions, it is shorted). If your meter has a diode setting, it should give you a reading (probably somewhere between 0.6 and 2.0) in one direction, and "OL" in the other. The resistors should, obviously, be close to their nominal resistance - usually they open when they fail, so if the resistance is much higher than it should be, it is probably bad. The varistors usually crack (or explode) when they fail, but you can also measure the resistance to make sure they're not shorted (very low resistance).

Let me know if you have any questions, and be sure to let us know how it turns out!

[DD-YATES]

Hey thanks a lot. It sounds like you know something more about these than the average Powcon owners do. I will contact that person to see how much a board is. I really thought it would be impossible to get parts for these. Then again part of me was interested in learning electronics. But being I don't know much I wouldn't get it right the first time and might even screw up the parts thats good on the board trying.

First of all, if you can manage to remove the remaining parts of the capacitors, the unit should still run without them. They are intended for voltage spike protection and, to a lesser extent, phase balancing.

So this is a type of circuit protection? Does this have to do with the fact that utility power is not a pure sine wave form? I'm just wondering what caused it to fail. I was welding with 5/32 probably not more than 145 amps. I understand these to be 100% duty cycle @ 160 amps. I don't see how I could have gone over that. But oh well.

[DD-YATES]

Hmmm, I just discovered a bad varistor. It's # 32 on the sheet and part # 902011-003. Mounted on Assy, PWB Cap Board # 102205-001, #4 on sheet. I will have to find out what the specs are to get another one and try and solder it on.


.

[ArcPowTech]

The duty cycle has more to do with the large magnetics (inductors and transformer) overheating, and usually the thermistors will kill the output to prevent any kind of failure caused by overheating. The capacitor failure seems to be limited to that particular brand (Evox Rifa) of capacitor. Other brands seem to be able to absorb spikes better without catching fire like these do. Never really figured out why, since they have identical specs.

The blown varistor is rated for 175V RMS, 10kA surge. These usually fail when the voltage across the SCRs gets too high, which could have been caused by whatever took out the capacitors, or it could also be something shorted or disconnected on the output. I would check the output diodes (CR11 & CR12) in the heatsinks on the bottom. Measure from one of the small heatsinks to the large one in both directions - if the resistance is low both ways, one of the diodes is shorted (you'll have to disconnect the transformer to find out which one). Also check for any broken wires or loose connections while you're down there. If you don't find any issues, then the varistor probably just did its job, and replacing it is all that's necessary - every surge through a varistor weakens it a little, so it might have just been worn out.

Good luck!

[DD-YATES]

Hey APT, Here's where I'm at so far. Since I've never tested diodes before I just want to make sure I'm doing it right. The below picture, is that my diode check function on the meter? I think it is but I've always used it as a simple continuity checker, it puts a beep sound out when your trying to identify and trace wires. That's all I've ever knew to use it for. So does it have a dual function?



When I use that meter function I placed the probes one way and then the other and got the following results. So according to the manual there is CR1-3 cathode to stud and CR4-6 anode to stud. Both sets tested one way but nothing the other way as it should right?


CR1-3
.462
.451
.453

CR4-6
.471
.463
.470

I could not find the CR11 and CR12 diodes you told me to check to save my life. They are mentioned one time in the entire manual under "Parts list for figure 16,
chassis plate assembly" on the fourth line with Assy, WR heatsink, 100215-001 but never in a diagram showing a picture of the diodes themselves. It seems to indicate that they are on the right hand side of the machine when facing machine. Couldn't find them topside so I flip the unit upside down, remove the bottom cover and look at the underside and I still couldn't find them. Are they visible from the topside or bottom? Do you maybe have a photo of them? What are they next to? Where exactly do I look?

Also I tried the method for testing the varistors and I got nothing at all on any varistors on the whole unit. Surely they cant all be bad. I tested on the lowest ohm setting while switching the probes from one leg to the other and it couldn't read anything either way.

Thanks again.

[ArcPowTech]

Yes, that setting on the meter is dual function - continuity (beeps when resistance is low) and diode checking. In the case of diodes, the reading is the forward voltage drop. Those look like good readings for the CR1-6 diodes. It also sounds like the varistors are good. If they were bad, you would have gotten a low resistance reading.

CR11 and CR12 are not easily visible. They are inside large aluminum heatsinks on the bottom of the machine. If you look at the bottom side, you'll see two sets of heatsinks, one on either side of the main transformer. The one with red and white wires coming out of the front is the SCR Assembly, and the one that the transformer leads and shunt resistor bolt onto is the "WR (Working Rectifier) Heatsink Assembly" (output diodes). If you look down between the heatsinks, you might be able to see the SCRs and diodes themselves (if you can see past the Nomex dividers).

Don't worry, you don't have to get to the actual diodes. You can measure directly on the heatsinks. Each assembly has one large heatsink on one side, and two smaller heatsinks on the other side. Measure from one of the small heatsinks to the large one in both directions. Or, as I should have mentioned before, the easier way to check the output diodes is to measure across the output jacks.

If you don't see any problems with the output diodes, you should just need to replace the blown varistor and the capacitors on the CF board.

[smithdoor]

Do you have a schematic you can post?

Dave

I was welding one day last summer with the Powcon 300ST. I think I was pushing it too hard when I was making some stands welding with 5/32 8010's, and suddenly I turned and looked, didn't hear a noise or nothing and black smoke was billowing out the backside of the 300ST, I quickly unplugged it. After much crying in my beer that night, the next day I took the cover off and found what the manual identifies as a Capacitor Filter PCB board with three small capacitors , three varistors, and six diodes and a few resistors. It has a part # of 100199-001 in the manual and printed on the board.




Everyone knows you cannot just run out and buy another board. So I would like to attempt to repair the board myself if I can get the right values for the damaged components on the board and get those components from a electronic supply house. I know nothing about electronic repair. I know I will need the right tools for the job though. I have nothing to lose if I screw up.

1. So has anyone ever repaired their own boards before and therefore has the knowledge and experience they could share, what tools are needed?

2. The only components with visible damage are the three capacitors. Does anyone have a Powcon with those values readable they could give me? (The 100199-001 board is the same on 300SM, 300SS, and several others I downloaded the manuals for.)

3. Can anyone with experience tell me how to test a varistor, a diode and resistors. These dont have visible damage but may still be damaged. All I have is regular VOM meters. Do I need something else to test with?

Anyone with electrical knowledge would be greatly appreciated.

[DD-YATES]

The only schematic that exists to my knowledge is the operators manual PDF @ https://www.mirabeliwe.com/downloads

[smithdoor]

I look at the schematic it for DC voltage
It looks like used on 3 phase welders too.
The good news it is simple to rebuild.
The manufacturer should have replacement boards as used on other machines.
You can find local electronic repair that can replace the damaged parts. All parts looks like they off the shelf.

Dave