Troubleshooting welder wire speed control

[Olsonkrist]

I have a 15 or so year old Campbell Hausfeld wire feed welder that I am trying to repair. WG3000 is the model number. The wire speed runs at the highest speed all the time regardless of where the potentiometer is adjusted. It might actually be running faster than full speed but I can't be sure. Replacement circuit board is no longer available, part number for that was WC402900AV. My first thought was the pot was just shorted and running full speed all the time but I am pretty much a beginner with electronic repair. I have done a lot of analog machine control work so I have a meter and know how to use it. I never got into any of the boards, everything in industry is just r and r anyway but I want to learn and decided this could be a good starter project. , but I ran into trouble determining the resistance of the pot, looks like it is marked 1 ohm to me but I don't know what IKA's annotation system is. No hot spots on the board anywhere. Any components I can test without removing from the board? Any help or ideas with the pot or if I should look elsewhere would be appreciated. I am working on making a circuit drawing of the board, but am not done yet.

Thanks,
Krist

 

[Heliman]

Theres not that many parts. Id pull them and check the transistor and caps.

 

[73's de Edd]

.



Sir OlsonKrist . . . . . . .


I'll bets all my munneys on the " bob tail nag" .

But my very HIGHEST suspicion is marked item #1 with secondary importance at item #2.
I would suspect that pot to be OK and minimally on UPWARD from a 1 K value..
Measure for the resistance from center pin to each opposite end pins and double the
highest value being read and consider that value being reduced by shunting resistance
from on board resistive current loops.
The question is if its rotation produces a definitive change from one end to the center position.

The units value could also be PRESSURE stamped on the metal shell of the control .

Pass us the writing on the semiconductor cases in order to determine if its being a TRIAC
or SCR for item1 and if item 2 Q1 is either a Diac or Unijunction transistor..
Use DVM or analog VOM for interpreting the intra terminal possibilities of 1, just like you would
when testing a transistor . . . . . . .and I am expecting a dead short being present between 2
of its terminals .

MARKUP:

Thasssit . . . . . . .

73's de Edd


.

 

[Olsonkrist]

Thanks for taking time to look! I really appreciate it.

I just finished ID on all the parts. They are as follows:
Your #1 is TYN412 SCR
Your #2 is MPSA42 transistor
Big cap is 100uF 63v
Small cap is 10uF 50v
1n4007 diode x2
1.8k ohm resistor 1/2watt x2
100 ohm resistor 1 watt
3.9k ohm resistor 1/2 watt x2
7 watt 4.7ohm resistor
-plus all the surface mount resistors on the solder side hopefully I don't have to mess with them.

After I wrote the initial message it dawned on me that the pot was labeled 1kA so 1k ohm with "A" slope right? "A" slope would be logarithmic for a pot in this age range correct?

Thanks,
Krist

.



Sir OlsonKrist . . . . . . .


I'll bets all my munneys on the " bob tail nag" .

But my very HIGHEST suspicion is marked item #1 with secondary importance at item #2.
I would suspect that pot to be OK and minimally on UPWARD from a 1 K value..
Measure for the resistance from center pin to each opposite end pins and double the
highest value being read and consider that value being reduced by shunting resistance
from on board resistive current loops.
The question is if its rotation produces a definitive change from one end to the center position.

The units value could also be PRESSURE stamped on the metal shell of the control .

Pass us the writing on the semiconductor cases in order to determine if its being a TRIAC
or SCR for item1 and if item 2 Q1 is either a Diac or Unijunction transistor..
Use DVM or analog VOM for interpreting the intra terminal possibilities of 1, just like you would
when testing a transistor . . . . . . .and I am expecting a dead short being present between 2
of its terminals .

MARKUP:

Thasssit . . . . . . .

73's de Edd


.

 

[73's de Edd]

.


Sir OlsonKrist . . . . . . .

I think that you are just going to have a crunched TYN 412 from its K to A and as a precaution, also check the two larger black 1N4007 diode units.

Parts:

And no, you would not want a log taper pot in that unit , you just want a linear change with rotation . . . .using a linear pot . . . . . a log pot would have a slow resistance transition all
compressed up at max ccw rotation and slowly varying until about 50% wherein it rapidly starts rising in value.

73's deEdd

 

[duke37]

I do not seem able to find if the TYN42 is a triac or SCR.
Am I mistaken that the marking of the connections on the board differs from the picture shown at the side?

Edit
Sorry, it is an SCR

 

[Minder]

I do not seem able to find if the TYN42 is a triac or SCR.
Am I mistaken that the marking of the connections on the board differs from the picture shown at the side?

A search shows up many app notes that show it as an SCR?
M.

 

[73's de Edd]

Indeed the unit is being an SCR / Thyristor . . . .and with it even utilizing an intelligent numbering system . . .wherein you immediately know of the 400 volt rating and the 12 amp current spec.
I overlaid some components from one side of the board to the other to relate a part to its solder lands connections.
That one part would have been better served by just using the G A K marking assignments.
If you do revolve and flip it . . . .in your minds eye . . . it will come out as it is now marked.
Thassssit . . . .

73's de Edd

 

[Olsonkrist]

Update- stuck again.
I tested the SCR, the transistor, both diodes, and both capacitors. All the tests indicated they were good, but I decided to replace the parts anyway just in case I was getting false readings. I tried the machine again and the result is the same, full speed wire feeding. 38v in from transformer, 32v out of board regardless of where pot is.

I have not taken the pot out and tested yet since that wasn't a suspect. I did test it in the board, measuring resistance between terminals A and C and get around 280 ohm all the way ccw on the dial and 1030 ohm with the dial all the way clockwise. A to B measures from 0-1030 and B to C measures 280-0 ccw-cw respectively.

I also removed the big resistor to test and resistance on that was 5.5 ohm vs. 4.7rating so within 15%

 

[Bluejets]

Did a similar wire feeder not long ago and it was a crook zener.
Looks like at least one on the underside, did you check these at all?

 

[Olsonkrist]

Did a similar wire feeder not long ago and it was a crook zener.
Looks like at least one on the underside, did you check these at all?

I did not. I am not sure how to ID what end is the anode and what the through voltage should be?

 

[Bluejets]

All you are looking for initially is an open circuit or a short ( the latter was in my case)
Set multimeter to diode test and check each one, one way and then the other.
A good diode may read around 350 one way and maybe 1100 the other.

 

[Olsonkrist]

All you are looking for initially is an open circuit or a short ( the latter was in my case)
Set multimeter to diode test and check each one, one way and then the other.
A good diode may read around 350 one way and maybe 1100 the other.

Do these need to be removed from the board to check?

 

[Olsonkrist]

I have a 15 or so year old Campbell Hausfeld wire feed welder that I am trying to repair. WG3000 is the model number. The wire speed runs at the highest speed all the time regardless of where the potentiometer is adjusted. It might actually be running faster than full speed but I can't be sure. Replacement circuit board is no longer available, part number for that was WC402900AV. My first thought was the pot was just shorted and running full speed all the time but I am pretty much a beginner with electronic repair. I have done a lot of analog machine control work so I have a meter and know how to use it. I never got into any of the boards, everything in industry is just r and r anyway but I want to learn and decided this could be a good starter project. , but I ran into trouble determining the resistance of the pot, looks like it is marked 1 ohm to me but I don't know what IKA's annotation system is. No hot spots on the board anywhere. Any components I can test without removing from the board? Any help or ideas with the pot or if I should look elsewhere would be appreciated. I am working on making a circuit drawing of the board, but am not done yet.

Thanks,
Krist
View attachment 25467 View attachment 25468 View attachment 25469

I am still working on this as time permits, I just had a question about the general function of the board. Is this a voltage dividing control or a PWM?