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Electronics help

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Bill in IL

Well-known Member
I am working on a Lincoln wire welder. Its a 120 volt portable weldpak 100. Its been a good machine but the wire feeder quit. I was able to locate components to repair the circuit card in the machine easily except for one.

I posted a pic of the remains of the component in question. Markings on it were 105K and +35 or +3.5. Not sure if its a precision resistor, capacitor, zener diode just never seen a component quite like this one.

Checked the manual at lincoln it shows wiring diagram but no schematic for the board.

8332.jpg
 
105k could be 105,000 ohms of resistance, or 105,000
picofarads of capacitance. the +35 is unknown as either would
have the tolerance marked like 1%, or 5, 10. or 20. 35% would
be something that an electrolytic capacitor would state, like the
very large start/run capacitors in an air conditioning unit. The
shaped end is not normal for either. Could indicate the cathode
end of a diode. A resistor or diode could burn like is shown in
the picture. The resistor usually burns in the center as does the
diode.

If it's a carbon resistor you can easily bend it and break it apart
right where it burned. If a diode it will be glass fused to glass
and won't break, it will bend.

Knowing what the rest of the circuit looks like could help in
understanding what role it plays hence what it is. A circuit
diagram would help even if you pencil it out by looking at and
identifying the other parts and show how they are wired to each
other.

That's the way it looks from here.

Mark
 
I think that's a tantalum capacitor. It's clearly a polarized device, as the ends are different.

What are its dimensions? That will help identify its value. The "105" is probably its value in picofarads. The "5" is a multiplier.
10 => 10
5 => 00000 (5 zeroes)
Add it all together and you have 1,000,000 pF, or 1 microfarad.

The "K" is a tolerance code. Probably 10 percent, I'm not sure.

The "35" is its voltage rating.

See if it looks like one of the capacitors on this page. You don't need an exact replacement, though, any 1 uF, 35V tantalum capacitor will do. Of course, there could still be other faults on the board that will blow your replacement cap.
Tantalum capacitor
 
Thanks... That was exactly the help I was hoping for.

The size of the device is about the same as a 1/4 watt resistor.... 3/8" long 3/32" diameter.

It would make sense to be a capacitor of some sort cause it appears to be a feedback circuit with a resistor on a across the input and output of a voltage regulator.

Thanks again.

Bill
 
Welding circuit boards are way over priced.Eriend brought in an Esab circuit board that had 2 rotary switches made as part of the board.A new board was 700 bucks, new welder 1100 bucks.Parmak brought out a new line of fence chargers.Wont give out circuit diagrams of complicated boards or even voltage points.They took out a simple input transformer and replaced it with 27 parts on a board.That part looks like a tantalum capacitor.I would put a new one in and see if the feeder works.Price a new board.I always look for a reason that a part failed in repairing electronic items.If the welder was left plugged in a lightning strike on the power line could have damaged the part.Lightning will jump ON/Off switches so unplug those expensive welder when done using them.
There are companies that repair welder circuit boards.Over the years Ive seen expensive fence chargers with parts ID wiped off parts.
 
That's a better answer. I think you are onto it. Can't disagree with a thing you said. I didn't do much with them in industry but fooled with enough at home to agree. Never saw one as such however; very peculiar case for what I have seen.

Mark
 
This board is relitivly simple. Quick web search showed 125 bucks to rebuild the board. Looks like parts will be 20 bucks with shipping. My best guess here is the voltage regulator shorted and took out the cap in the picture along with a 15 watt resistor. Going to put in the voltage regulator and power transistor and hope it works. Welder could be replaced for 350 bucks so its not worth putting much into it.
 
Bill,

Your scenario (blown VR) sounds likely to me.

The dimensions you gave for the device matches up pretty close to the data sheet for the Vishay tantalum cap. If I read the data sheet correctly, a 1 uF, 35V cap is .110 inches in diameter by .290 inches long (you said .09 x .325).

It won't hurt to bump the voltage rating up to 50VDC.
 
The wire feed is controlled by variable dc voltage to the motor.Welders with a circuit board are bad news.I bought my Miller 130 used.If you had a schematic you could do the repair easy.If you do get it fixed make a diagram and take some voltage measurements.Dont leave the welder plugged it when its not being used.Lightning strikes on the power line jump the on off switch and destroy parts.The pass tranistor can be checked for shorts.
 
Mark you are confusing me. I thought you nailed it to a Tantalum capacitor and now you are talking about a VR.....i.e. zener diode for a component to me....or do you mean that the failed circuit containing the Tantalum capacitor is the VR for the welder feed??????

Mark
 
I doubt you will find a 105,000 ohm resistor.At least not in a motor control circuit.The are several ways to fix the problem.Make a new circuit board from scratch.Get a look at another welder like it.See if Lincoln will provide a schematic.
 
Hey Tex,

I was responding to Bill's statement:

"My best guess here is the voltage regulator shorted and took out the cap in the picture along with a 15 watt resistor."

So there's apparently a solid-state regulator on the board that possibly failed, taking out the filter capacitor. I already assumed the capacitor was some sort of power supply filter, due to its large capacitance value. Polarized capacitors usually fail from either overvoltage or reverse bias.
 
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