Esab Handy Tig 180 AC/DC overheat/thermal switch issue

[Andreas D]

Hi,
I recently bought a cheap Esab handy tig, which has some sort of problem with the thermal switch circuit (I think). When the machine is powered on fan starts and the leds light up, I can toggle the functions etc but the warning light for overheat stays on. I get no output from the machine (either tig or mma). According to the service manual there’s three thermal switches. Is there any way to bypass these switches? The service manual claims some damage could be done (Photo from manual attached).

 

[Seadog]

If you can find them then link across them. Watch for smoke

 

[eddie49]

Two of them are right there in the third picture, stuffed into the heatsinks, and the solder joints 11 and 11-1, 12 and 12-1 are at the edge of the board. I am not sure about the third one, maybe it is connected to the two solder joints at the left-hand corner of the top board. I would start by checking for continuity across these thermal switches. Note that sometimes a "Thermal Fault" LED is also used as a general error indicator.

 

[Jan-DIY]

The 3rd one is placed basically in the lower section of this Machine (Lorch Handytig210AC/DC)
Will try to find a picture.
As i can see from circuit diagram first ST1 and 2 are monitored. After one cuts out ST3 gets into circuit because of RE2.
Only if ST3, ST2 or ST1 cuts out you got this error.
Sounds tricky.
Got 2 of them here.
One in working condition.
But both in 2nd hardware revision.
Not easy to service this ones because of limited space.

 

[Jan-DIY]

Pro tip if this one gets back to life.
Replace 2p torch socket to 5p Tuchel eg.
You can then add second torch-button funktion to this machine.

 

[Jan-DIY]

Here it is.
These thermal switches are highly reliable.
Dont think that they caused the fault.

 

[Jan-DIY]

Have a look at the ribbon cable from first to second pcb.
Seems that one screw hitting a trace?!

 

[Andreas D]

Have a look at the ribbon cable from first to second pcb.
Seems that one screw hitting a trace?!

Thank you for your reply, you are correct, the ribbon cable is slightly damaged but not broken off. It seems a bit complicated to dissasemble the machine without doing more damage to the ribbon cables. I try to do as much as possible with the machine as it is for now. These thermal switches, are the normally open?

 

[Jan-DIY]

Hey Andreas.
They are NC.
Please check proper insulation of the cable. If the screw shorted this insulation it gets short to Earth potential and may destroy something.

 

[Andreas D]

Hey Andreas.
They are NC.
Please check proper insulation of the cable. If the screw shorted this insulation it gets short to Earth potential and may destroy something.

I will do that. To check the switches for continuity i guess i have to cut the cables to get them isolated from the circuit?

 

[eddie49]

It is true that the sensors are connected to a circuit which contains other components, and these things could be in series or in parallel with what you are measuring. However, you are going to be checking the sensors for a short circuit ( if they are OK ), and that condition - zero Ohms - trumps all others!
You can just put the meter across the sensor ( pierce the wires with pins if you have to ) and look for something close to 0.00 on the Ohms range. If you get that, the sensor is OK. If the sensor has "stuck" open, then you will get a much higher resistance reading, which will indeed depend on whatever other components are in the circuit, but by then you will know that the sensor is faulty.

 

[Jan-DIY]

You can bridge them all to see what happens.
I would also remove the resistor near St1 and 2.

 

[Andreas D]

So i measured resistance, in the range of 200 Ohm (thats the only range that would give me something) and on the soldered spots for the cables on the circuitbord, yellow cable gave me 3 Ohm and the the two pair of white cables gave me 0,1-0,2.

 

[Andreas D]

I also tried to see if i could se any visible damage on the circiutbord on the underside of the machine but it looks like new.

 

[Andreas D]

I also found two ”coil-things” looking a bit dull compared to the third of them.

 

[Jan-DIY]

These are gate drive transformer for galvanic insulation.
Never had a failed one.

 

[Andreas D]

Well some slight progress, the lower part of the machine is internally coated with magnetic dust. Will clean and blow with compressed air.

 

[Jan-DIY]

So I got triggered to get my broken Lorch out of my collection.
same behavior.
It looks like PFC stage not working properly but Mosfets doing fine.
Pain in the axxxs to repair these machines.
Really not that fun.

 

[Jan-DIY]

Small feedback on this issue.
There is a problem in primary SMPS an may also in PFC driver.
The shutoff is caused from charging PTC.
Got some broken Z and maybe PFC driver.
Add them to my BOM on Mouser but is not complete for shopping because next machines also need spares.

If you like then I can send over to you a PCB from a Handy S201.
Same PFC and SMPS topology as Handytig.
It is primary death because somebody shorted some leads to ground but main SMPS basically working. As far as I can remember...