BOC (Kempii) MIG 190C

[Richie Plewka]

Hi,

I recently purchased a 'Spares or Repair' BOC MIG 190C. I suspected it to be the PCB and it was cheap so thought I'd take the risk.

From what I've found on the internet these machines are re-badged Kempii machine.

Unfortunately, when I stripped it down someone had already had a go at the PCB. The relay had been replaced with an external (not PCB mounted) relay and the transformer had been removed. So I have no idea what components to use to replace the missing parts.

Does anyone have experience with these boards - labelled 'W000437 A'? What I'd really like is a circuit diagram and component list. But laking that a suggestion of what components (relay and transformer) they might be. Or if it is in fact a re-badged Kempii machine, which model and then maybe I can investigate the PCB using a Kempii model number.

Any help/diagrams/suggestions/pictures of your PCB - anything, really anything gratefully received.

Picture of the board with missing components attached.

Thanks,

Richie

 

[Bornfree]

I've got a BOC 250c and it's made by Kempi. But the PCB looks different to yours. Have a look on the kempomat 2500 thread I unloaded a picture of it.

 

[a111r]

You'll probably get some experts with advice on the replacement components to use along shortly.

Your other option if repair fails is a generic Tec Arc board, they do two types, as used in their various branded machines, e.g:
https://www.ebay.co.uk/itm/UNIVERSA...453795?hash=item1a799c91e3:g:GbAAAOxy~iJQ~bLI

https://www.ebay.co.uk/itm/UNIVERSA...426901?hash=item1a79baad55:g:ZEQAAOxywbNRBDm7

 

[Bornfree]

You'll probably get some experts with advice on the replacement components to use along shortly.

Your other option if repair fails is a generic Tec Arc board, they do two types, as used in their various branded machines, e.g:
https://www.ebay.co.uk/itm/UNIVERSA...453795?hash=item1a799c91e3:g:GbAAAOxy~iJQ~bLI

Tec arc also do a PCB repair service

 

[Richie Plewka]

Thanks. I looked for the kempomat 2500 thread picture but couldn't find it - sorry new to this forum, will persevere. I'm waiting for a reply back from Tec Arc.

I looked at the universal boards but I'm concerned that they don't do everything my machine was designed to do.

 

[tom2207]

I think it would be worthy of a professional repair on the board , at least then you know what youve got , they probably could tell you if thats actually where the problem was too . oOf course , if they dont find anything , or even if they do you then have the dilemma of dare you plug a newly repaired and tested board into an unknown machine ... me , id go for the gamble.

 

[eddie49]

Hello and welcome to the Forum. It must be disappointing to discover that someone has had a go at the machine already.
I would agree with other member's suggestions that using the TecArc PCB repair service is probably the best solution, with the caution that the PCB may not have been the actual, or the only, original fault. It is unlikely that both a relay and a transformer failed at the same time.

Small hobby welders use a PCB-mounted transformer rated at two or three Watts to drive the relay that powers-up the machine when the trigger is pressed. The main welding transformer then also runs the wirefeed motor, via the speed control part of the PCB.
On larger professional machines such as the Kemppi there is normally an auxiliary power supply that runs the control part of the PCB, the power-up Contactor, the wirefeed motor, and the gas valve. This power supply is typically a transformer rated at 50 or 100 Watts and 24 volts, about 3" square, plus a bridge rectifier and smoothing capacitors - often on the PCB. There may also be voltage regulator chips providing lower voltages to run logic for spot/stitch/burnback timers. Does your machine have a second transformer like this?
[ Note, this is not the inductor ( choke ) in series with the high-current welding output.]

Your machine seems to be a crossover, where the PCB-mounted transformer runs the power-on relay and the logic on the board. To confirm this, you would need to trace the printed tracks from the transformer connections. There will be two AC mains inputs for the primary, and then two, or more, low-voltage secondary connections. These may head to the top left corner of the board, joining to 4 diodes ( for the bridge rectifier ) and one or more smoothing capacitors. The transformer output is probably 24v; you may be able to confirm this from the voltage rating of the capacitors.
Is the replacement off-board relay large enough to control the main power transformer, and wired directly to it, or does it run a Contactor?
What is the coil voltage marked on the off-board relay?

I have not found any details or diagrams for that Kemppi PCB. Could you post a photograph of the part number markings on the board?

 

[Richie Plewka]

Hi Eddie49,

That all makes sense and helps put it into context without a circuit diagram.

My machine doesn't have an external power supply or transformer, the PS transformer is mounted on the circuit board and the bridge rectifier and smoothing capacitor (rated at 63v) are also mounted on the circuit board. The cooling fan is 230v and it's PCB mounted relay is 24v so my best guess is the transformer is 24v. I agree that it's unlikely for the relay and the transformer going at the same time is pretty unlikely, but the guy trying to fix it put it back together without the transformer thinking it might work - I've since had a conversation with the guy that sold it to me and 'a friend' helped him fix it! So I'm not too sure he knew what he was doing?

After a bit of detective work (measuring the distance between the transformer circuit board pads and comparing it to available options) I've come to the conclusion that it's a 3.5 watt transformer. It's a cheap part so I'll give it a go and report back.

The bodged on relay is rated at 30a at 240v and switches neutral to power up the arc transformer, it doesn't have another contactor. So I'm hoping this will be ok. I won't try to reinstate the PCB mounted relay - I can't find out what it is anyway - and it makes it easier to replace in the future if I do manage to get it working that is.

Thanks again for your help. Photo added of the back of the PCB showing the numbers.

 

[eddie49]

My machine doesn't have an external power supply or transformer, the PS transformer is mounted on the circuit board and the bridge rectifier and smoothing capacitor (rated at 63v) are also mounted on the circuit board.

Photo added of the back of the PCB showing the numbers.

It is unusual for pro-level machines to run the wirefeed motor from the welding output, since that voltage varies with the setting of the power range switch, and it also fluctuates as the arc length varies during the welding process. The wirefeed motor is probably rated at 30 to 40 Watts, so cannot be driven by the PCB power. I guess Kemppi rely on DC smoothing capacitors on the arc supply ( if present ? ), and a stabilised wire speed controller.

Using that part number, I have found a Polish welding wholesale company ( http://www.spaw.info.pl ) that listed a complete replacement W000437 PCB in their 2008 Kemppi spare parts catalogue:

http://www.spaw.info.pl/zdjecia/kemppi/Cennik_czesci_Kemppi_2008_v1.pdf

Nr katalogowy________Nazwa___________Min zamówienie____Cena netto zł
W000437...........PLYTKA BOC MIG 190C...................1.......................1580,35

That listing was a long time ago, and not cheap at £310, but I suppose they were genuine Kemppi parts. Anyway, it sounds like you have a good plan to progress the repair.

 

[Richie Plewka]

There are a couple of big capacitors next to the heavy duty rectifier and arc transformer in the bottom section of the welder so I guess that's how the voltage to the wire feed motor is regulated?

Thanks for the Polish link. I might chase them and see if they have a new board kicking around if my fix doesn't work - not sure the fixed welder is worth £310 though.

I got a manual from BOC NZ. They described it as a users manual but it details the parts. It details the BOC MIG 170C as well. I've included it incase anyone else is interested.

I'll let you know how I get on with the fix.

 

[Richie Plewka]

The transformer arrived - turned out to be 2.3VA transformer, fitting it and hey presto everything works as it should!

A big thank you to Eddie49 for your extremely prompt replies and your ability to share your excellent knowledge for welder electronics.

 

[eddie49]

That is great news ! Thank you for the update and your kind words. I am pleased that your BOC/Kemppi is working now and was a good purchase.

 

[ScottG]

There are a couple of big capacitors next to the heavy duty rectifier and arc transformer in the bottom section of the welder so I guess that's how the voltage to the wire feed motor is regulated?

Thanks for the Polish link. I might chase them and see if they have a new board kicking around if my fix doesn't work - not sure the fixed welder is worth £310 though.

I got a manual from BOC NZ. They described it as a users manual but it details the parts. It details the BOC MIG 170C as well. I've included it incase anyone else is interested.

I'll let you know how I get on with the fix.

This manual is helping diagnose my BOC190 thanks Richie !

I particularly found this advice helpful: c. Check the voltages, connectors X3/2 - X3/8 and X3/10 - X3/9 on the control board. If the voltages are incorrect, the transformer is faulty

 

[Ratz81]

There are a couple of big capacitors next to the heavy duty rectifier and arc transformer in the bottom section of the welder so I guess that's how the voltage to the wire feed motor is regulated?

Thanks for the Polish link. I might chase them and see if they have a new board kicking around if my fix doesn't work - not sure the fixed welder is worth £310 though.

I got a manual from BOC NZ. They described it as a users manual but it details the parts. It details the BOC MIG 170C as well. I've included it incase anyone else is interested.

I'll let you know how I get on with the fix.

Howdy
Recently got myself secondhand box 190c. Do you have copy of the user manual?
Can find one anywhere online
Cheers

 

[slim_boy_fat]

Howdy
Recently got myself secondhand box 190c. Do you have copy of the user manual?
Can find one anywhere online
Cheers

Welcome aboard, fella. A bit of a thread resurrection, as the OP's not been seen since 8th Aug last year.

Good luck with your search.