MinarcTIG 180MLP blowing fuses..

[bushtor]

Hi,
I have been working with electronics for 50- years, and I am not willing to hand over my beloved Kemppi to an expensive repair shop without giving it a try myself.

I really need a detailed schematic of the main board, or comments of the function of the components below. First a picture of my main board:

I first thought that these two components were surge protectors / varistors, but when I washed away the burnt carbon I saw that their silk-printed reference numbers on the board were R13 and R14. They looked like this:

If these really are PTC resistors I cannot understand how they could have the 'power' to flip a 16A circuit breaker...

So my question here is:

Does anyone here have a detailed schematic of this main circuit board, especially of the primary rectifier area. Furthermore I would need a component list, to know the specs of R13 / R14. I'm ready to replace the rectifiers, IGBTs and their gate resistors but I need to understand the circuit functions before deciding what to replace.

Thanks for comments :-)

bushtor

 

[TryingToWeld]

It's a 25 ohm 2a 380v PTC Thermistor, see https://latinafy.com/products/ptc-termistor-ptcb750-b750-25ohm-2a-380v/ for more details.

At a guess I would assume it's protecting what you have labelled as the 'Secondary Rectifier', so I would check them all for a s/c.

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[eddie49]

Hello and welcome to the Forum!

Hi,
I have been working with electronics for 50- years

Me too!

I think that these two PTC resistors ( thermistors ) are part of the soft-start circuit. They limit the initial power-on current surge as the capacitors charge, and are then bypassed by a timed relay.
The AC mains input circuit will contain a filter, the soft-start circuit, a bridge rectifier, and the smoothing capacitors.
The soft-start thermistors being burnt, and/or the supply fuse or circuit breaker tripping is usually caused by excessive input current due to a shorted component further along in the inverter power section. This is often one or more of the MOSFET or IGBT power transistors.
Please note that when one of these power transistors shorts it can feed the high DC voltage ( known as the DC link or bus, 325v ) into the gate driver circuits and damage them, and unless corrected this in turn will destroy a replacement transistor. There are some notes about this in Post #66 of this thread:

M

Thread 'Repair Lincoln V205T AC\DC Main IGBT Inverter Board'

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Hi, after long time later, just start again try to repair my roasted main pcb ( called by Lincoln Main IGBT Inverter Board ) of Lincoln İnvertec V205T AC/DC welding machine. I want to try to share my knowledge and experience. First off all i need to circuit diagram roasted section of pcb which is called UPFR section. Many times searched to internet and can not find any information of correct version of this machine. And decide to draw scematic diagram of this section. I hope that if somebody need it and help out this circuit diagram. Also hoping that more people contribute and develop...

• Mustafz
• Replies: 73
• forum: Miller, Lincoln, Hobart

• 

For general hints about this type of issue, use the Search box at top right for "inverter repair".

 

[bushtor]

Hi,

Thanks for the replies! My main board image is copied from Kemppi's service manual, which I found here:

https://optimumelectro.ru/files/Kemppi/Kemppi_minarc_tig-180-mlp-service-manual.pdf

I agree fully with your softstart theory. But it would be a lot easier having a detailed schematic which shows how everything works together.

Does anyone here know if Kemppi's documentations policy is to keep their electronics' inner workings as well guarded secrets, or would it be worth the time to search for such data on the Net..?

best regards bushtor

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