200A AC/DC TIG Welder

[Junkers]

Hi all

I have a welder here that I'm looking at repairing. It appears that one of the components on the control board has failed and is draining current causing one of the regulators to overheat, and is triggering the HF/HV start (triggers on a low signal). I've tried feeling around for any warm components but unfortunately nothing has given any clues. I've also tried unplugging various peripherals and haven't had any luck. What I'd like to know is if there is anyway of tracing where the current is being sunk? I've thought about buying a thermal imaging camera but don't necessarily want to shell out several hundred dollars on a guess. Are there any tips or tricks you guys can recommend?

Here's what I'm up against.. Unfortunately the traces of interest are on the underside of the board.

[fenugrec]

Are you pretty sure the short is on the CB ? Can you isolate which supply rail is shorted ? It'll help also if you can rule out whether the power section (IGBTs more likely, maybe MOSFETs) is shorted out too.

Once you have a better idea what signal is shorted, you can measure resistance along that signal to isolate the fault. You'll need a reasonably sensitive ohmmeter for this. If you only have a good voltmeter, just feed some stable current through the short and look for the largest voltage drop.

I think Dave does something like this in a recent repair video on a "Data IO" or "uni data" universal programmer (I forget the name).

[coromonadalix]

as i can see on the photo, near the number 54 and 59 yellow transformers, you seem to have 4 outputs of somekind,  pull the 4 plugs,  white balck, green black, blue black, gray black ... do a current test

Your main outputs transistors maybe under the board ?? or follow where they go ??  you'll have to dismantle it further i think,  just to add luck  the chips seems buffered   

See this as an giant pwm controlled power supply,  you can adjust the width pulse maybe the pulse height   etc ...

[HUGOMAN]

HI TO ALL

I see that you have a lot of work with this welder ! i guess it's a Chinesse brand,  did you weld on dc normally ?

good luck

[tron9000]

This seems familiar.

Back in 2006-07 I used to inspect/modify units like these before shipping. Do you have any more photos of the sides with the lid off? Any part numbers? Cos they're are a generic, rebadged unit and a schematic might exist.

Usually the IGBT's are bolt to a massive heatsink which hangs under the broad photoed.

I assume when you say regulator, you mean one of the devices stuck to the heatsinks in the middle of the board?

If i remember there is a thick conformal coating or varinsh on these boards so if you want to start probing around best get a sharp set of probes!

[Junkers]

Thanks for all your input. The unit is identical to the one shown in the video posted below. Yes, it's a Chinese unit  . One that cost a little too much to just throw away.

Are you pretty sure the short is on the CB ? Can you isolate which supply rail is shorted ? It'll help also if you can rule out whether the power section (IGBTs more likely, maybe MOSFETs) is shorted out too.

I'm reasonably certain that the short is on the board as I've had most of the plugs disconnected and found there is still excessive current draw. The other plugs I'm not comfortable with disconnecting with the system powered up. The last thing I would want is for something to latch up and go bang. At present, I've had to resort to breaking the tracks and have managed to identify a 2 ohm short. I've narrowed it down to the left hand side of the board (as per the original post) but haven't looked at it since. I broke the circuit into several elements and found the 2 ohm short to ground appears in two regions. I'll have to do some further investigating.

as i can see on the photo, near the number 54 and 59 yellow transformers, you seem to have 4 outputs of somekind,  pull the 4 plugs,  white balck, green black, blue black, gray black ... do a current test

These drive the HV inverter gates. I've had them disconnected and it had no impact. I'll see if I can get my hands on a decent power supply / voltmeter and give your test method a go.

I see that you have a lot of work with this welder ! i guess it's a Chinesse brand,  did you weld on dc normally ?

I can't answer that for you, it's a friends welder.

This seems familiar.

Back in 2006-07 I used to inspect/modify units like these before shipping. Do you have any more photos of the sides with the lid off? Any part numbers? Cos they're are a generic, rebadged unit and a schematic might exist.

I have a schematic here but it only details the main driver and the outputs of the control board. The part number on the board is WSME 200C. WSME 200 is a common part number for Chinese welders but it appears that they've evolved somewhat, nothing that I can find resembles what I have here.

I assume when you say regulator, you mean one of the devices stuck to the heatsinks in the middle of the board?

If i remember there is a thick conformal coating or varinsh on these boards so if you want to start probing around best get a sharp set of probes!

Yep, those are the ones. A pair of 7815 linear regs. It's the one obscured by the other heatsink (right hand side) that is rising in temperature. Yes, that varnish is everywhere and creates a real mess when trying to desolder anything. They've coated the ICs with it as someone mentioned above. It's shrunk back so the embossing on most chips is visible. The large 14 pin DIPs are D flip flops and the 8 pin DIPs are mostly Op amps.

[tron9000]

if you remove the connector circled below, does it still HF start? Least then we can eliminate that board.

[Paul Moir]

I have a near identical board that's non-functional but for a different reason; something was shutting it down with an over temperature indication.   I thought I was pretty close to finding the fault before the replacement board arrived.  I also have a functional one inside the welder, and I really ought to go in there and do some cleaning & maintenance soon.   Let me know if I can be of any help measuring or identifying anything there:  I can tell you that 7815 rail is at high impedance on mine so 2 ohms or anything near it is not natural.

[Junkers]

if you remove the connector circled below, does it still HF start? Least then we can eliminate that board.

Yep, I've already disconnected these wires. Yes, this does kill the supply to the HF start. The power supply fed by these wires dictates the state of the HF start, there's no separate logic input.

This was the first part of the circuit I looked at before realizing the regulator was quickly heading toward overheating. The power supply to the HF start board is triggered by a low signal fed into an opto isolator which drives a BJT, which controls a mechanical relay used to drive the HF start daughter board. Since there is a short present elsewhere in the circuit the opto isolator is effectively seeing a low signal and thus is being switched on. So unfortunately this problem is only a symptom of the actual issue and isn't directly related itself.

I have a near identical board that's non-functional but for a different reason; something was shutting it down with an over temperature indication.   I thought I was pretty close to finding the fault before the replacement board arrived.  I also have a functional one inside the welder, and I really ought to go in there and do some cleaning & maintenance soon.   Let me know if I can be of any help measuring or identifying anything there:  I can tell you that 7815 rail is at high impedance on mine so 2 ohms or anything near it is not natural.

Thanks! This could be very handy... I'll have another plug at it this weekend and see how I get on. 

[nebv66]

Hello, I know that this topic it's a very old one. Did you find the broken item on your board? I have a similar situation with the same welder ...Only the short to ground has 5 Ohms.
I will try to supply with 5-8V and check with an infrared cam if something will be warmer. THX, best regards

[Paul Moir]

Not the OP but I'm still here and I still have the board & welder if I can help.

[nebv66]

I changed a LM7815 and the LM324 and now the welder it's running again. Tho OP (LM324) had 57Celsius by supplying with ca 5V on the output of LM7815 (without LM7815), so I changed it.
The two LM7815 place on the black radiators are running warm and one capacitor in ther proximity (2200microfarad) is not very good placed. I changed it also.

THX for your answer
Best regards