Lincoln TIG 200 Square Wave repair

[mb443]

I'm not a pro and using my welding machines for hobby.
My Lincoln TIG200 square wave was occasionally used and currently is arcing between pin1 and pin2 U07 PWM chip 5M0380R and burns resistor R076 (1ohm 5W)on top control board. This happens due to full AC voltage comes to pin2 through rectifier. There is a cut in PCB creates 1/16 air gap around the pin2 but it only helps for a month of use or so. It looks like Lincoln put that resistor into design in series with primary coil to limit current and burn if current exceeds as a fuse. As I heard the newer boards have a fix for this weak spot in design.
I wanted to open a conversation on details of design for TIG200 If anybody heard what did they modify for fix that issue or other issues please share details. I'd like to upgrade mine as tired replacing those 5watt resistors on my out of warranty TiG.

[Hobbytime]

did you call lincoln to see what they recommend???? doesnt matter if its out of warranty..advice is free from them...

[mb443]

did you call lincoln to see what they recommend???? doesnt matter if its out of warranty..advice is free from them...

Thanks Hobbytime, but I've had a few attempts to acquire a service manual without much of a success earlier and I guess I just assumed that for any repairs Lincoln wants everybody who owns these machines to go exclusively through them otherwise they would of publish schematics. I'll definitely make an attempt to contact them following week. This time I need to replace U07 chip in addition to R076 as their snubber doesn't protect from back emf from primary coil at all and I have currently no 24V on fan consequently 15v down w/ no voltage on PFC Power module. And I need my welder working now.
Currently my replacement chips are in the mail and have a few resistors to replace left, so I can get my welder back online next week, the question again is for how long...
I will try to contact Lincoln and hopefully they will not offer to replace the whole inverter board (which most likely they will) w/ waiting period of a few months because it's assembled in Mexico etc as per other posts. I actually also doubt that they'll share an updated design, but won't hurt to try.
Thx again for a quick reply to this post, regards, mb

[CAVEMANN]

Welcome!

[mb443]

Just wanted to conclude on the initial post that after I replaced chip U07 (5M0380R) and put it onto radiator as per design (PCB mask shows U07 is on radiator) along with new resistor 1ohm 5W (R076) my machine is in lot better shape now.
I will continue this thread if I'll face any issues again, but so far I can't complain.

Future plans include update to modify my welder w/ making "post flow" adjustable. And next I'll make that big FAN proportionally controlled by thermo resistor attached to hottest element on the board.
Wondering if anybody tried that...

[mb443]

I was just thinking why Lincoln does not include schema with their machines or at least publish schematics on their site. I don't own Miller but I've heard from owners that Miller does include detailed schematics with their machines which is definitely a huge plus...

[mb443]

Below published fragment of PCB where damaged parts replaced for those who is willing to fix their machines without high price tag of replacing the whole inverter board.

[mb443]

On picture attached it's easy to locate U07 & R076 in bold yellow

[mb443]

As of Amptrol K870 pedal then there are lots of confusions that Lincoln made a mistake on the side print of wiring diagram under the cover.
Well, it is all CORRECT, and the reason many say it is not that the schema on the side of the machine is for internal board from machine side - that's why colors do not match.

The actual schema for pedal is below w/ colors and plug shown from the opened plug side.
Also, the pedal itself is not too sophisticated internally it only contains a potentiometer and two switches. The Second switch just insures when pedal is in initial position (current at MIN) it shorts the potentiometer and prevents accidental current fluctuations.

Hope this helps to some who is fighting with proper soldering of their cable for AMPTROL K870 to the plug.
Best regards, mike b.

[mb443]

Small addition made to above solution to avoid arcing between pin#2 and pin#1 connected to common.
The small piece like 1/4" of high voltage rubber shell taken from old TV flyback transformer put over pin#2 before U07 installed.
This works better in addition to PCB cutout providing air gap around the pin2.

[Speed51133]

Could you post your source for the new components? Also, do you have any pics of you "fix"? Is the air gap that crescent moon slit in the board? How do you solder in the new chip and resistor without access to the rear of the board?

[Speed51133]

Could you post your source for the new components? Also, do you have any pics of you "fix"? Is the air gap that crescent moon slit in the board? How do you solder in the new chip and resistor without access to the rear of the board?

Oh well, got my two machines covered by warranty. They essentially replace EVERYTHING under the cover with newly designed components.

[Speed51133]

Well I tried to see if my machine has the same issue. It didn't. Anyone want this??? Can't upload an image but it's the entire guts of the machine

[Speed51133]

[mb443]

I do realize it's little bit late, anyways here is an updated picture with two parts replaced in red.

[oz4zoe]

hi, did you have success with a circuit diagram ?

I have the problem that AC no longer works.
the IGBT's seem to be ok, the dual diodes are fine too.

now i am at the point where a schematic would be really helpful.

[mb443]

Hi, oz4zoe,
I didn't get anything from Lincoln support other than general info and once they learned that my unit out of warranty forwarded me for service to local place.
so, I started to learn the unit and getting into understanding of the way unit designed and function but as I have free time which is limited.
Anyways, my unit is having the same problem and as far as I've learned is the weak elements are those controls are opto-couplers which are easy to test even on turned off unit as a first step, but definitely need to remove some of that caulk looking stuff near the pedal connector (marked as a "key" on a top board).

[mb443]

Here is fragment of the top board w/ all control opto-couplers related to control signals in red which I'd check first.

Please keep updated on progress.

[mb443]

oz4zoe, I wanted to add anther guess what you can try to investigate.
With HF board disconnected, just disconnect any wire coming to HF board and with portable oscilloscope (or at least the one you're using is connected through isolating transformer), and check how is output signal looks like, to make sure both halfs (pos + neg) are equal.
I assumed that you've tried to

reset your unit to factory settings (if not you can try it as follow):
= While the machine is powered up: hold the Mode Button(AC, DC, TIG, Stick)in for ten seconds.
= LED's will scroll in a 1,2,3 pattern.
= After about 10 seconds there will be a pause in that scrolling pattern.
= Release the mode button, if the reset was successful the meter will read 100 amps if hooked to 230V and 90 amps if hooked to 115V.
Machine has been reset to factory specs.

[oz4zoe]

Thanks to all the information so far,

and yes, as my testing has progressed, I have found one of the A3120's to be defective as well as the zener diode for it.
I will try later to measure the value of the zener diode of the complimentary section. I was able to solder both out in one piece.

is there anything that speaks against using a dip8 socket ?

[oz4zoe]

I measured the diode, it is a 6.1V zener diode. as far as I can tell.

[oz4zoe]

ok I will briefly describe how I proceeded.

since I do not perform a test under power unless necessary, I reverse engineered and measured.

measure from the source of the error backwards:

i started with continuity/diode measurement which are the switching components.
then find out what the switching elements are: igbt RJH60F7
measure the igbt C-E , E-C , ...
the results are all in explicable range.
the next step was the driver of the igbt.
Here I found out that one A3120 was faulty on the output side.
I desoldered it and found out that the diode D20 had a continuity in both directions.
because she is installed in reverse direction, I suspected a zener diode.
desoldered the diode of the parallel circuit and measured today.

I hope now the rest is ok.

what iritates me a little, is the use of the CD40106 Schmitt Trigger ?

[oz4zoe]

The welder is running again.

I have replaced both zener diodes with a 6.2V 1W
and a new driver with a 3A header.





the workpiece was not cleaned to see the cleaning effect of the balance

[Mact1200]

Hi, i have the same problem. Q06 not have a idea this referen. This component short circuit. You have idea the referen please?

[oz4zoe]

sorry I can not find a Q6 on my pictures.
the welder is already reassembled otherwise i would check what area is your transistor in.

if your component has a mirrored component in a parallel section, you can solder it out and measure it non-destructively.

A GM328 tester is a good start to find out what type of component it is.

If your Q6 doesn't have a parallel section, I would systematically examine where its signal comes from and where it goes to create a schematic to determine its function.


and no, I have not found a circuit schematic anywhere, only what I have created myself.