Troubbleshooting Kemppi minarc150 welder circuit

Thread Starter

Melker.Jonsson

Joined Sep 1, 2018
6
Hi!
Ive been staring at this issue the last two days.
The welder is just a few years old and warranty expired not to long ago.

This is the circuit diagram for the welder:
https://obrazki.elektroda.pl/5761016100_1518434478.png

The welder just wont turn on. X1 and X3 at the top is power in, 230v ac.
Relay K1 top left corner is the power relay wich turns it on.
R30 and R23 is PTC's. They gives power to the start up procedure.
R23 triggers the second that power is applied and cuts of the rest of the circuit.

X13 and X12 is primary winding of transformer, X6 and X8 is secondary, X14 and X15 is another secondary AUX winding.

I got limited knowledge regarding circuits and electrical components. Im happy for any input anyone can have.

This is an service manual:
http://valvolodin.narod.ru/schems1/kemppi_minarc_150-vrd_151_ver-11_sm.pdf
 

Dodgydave

Joined Jun 22, 2012
9,694
N2 (Uc2844) is the smps chip pulsing the transformer with the transistors V4, to V10, you need to check if this chip is working , ideally with a scope, but try using a Dvm on AC at the output of the chip on pin 6, the supply is 20VDc on pin7, see if you're getting 80V at the output of the transformer secondary across the bridge rectifier output X7,9.
 

shortbus

Joined Sep 30, 2009
8,060
Melker.Jonsson, did you go through the trouble shooting list on page #7 of your second link? You will need a minimum of a voltmeter to check beyond that, starting at page #10. That manual is much better than most I've seen.
 

Thread Starter

Melker.Jonsson

Joined Sep 1, 2018
6
Dodgydave, i will take a look at the smps chip. What happens is when i give it power on x1 and x3 the R23 thermistor shuts down instantly. So im not getting any voltage to the IGBT's (V4 toV6) or the primary of the coil.

This is from the service manual.
Minarc power sources are”dual-Forward”
inverters, controlled by PWM technology.
Switching components are IGBT transistors. The operation frequency is ~ 80 kHz

I dont think i can measure that with my multimeter. I could try get hold of a scope.
 

Dodgydave

Joined Jun 22, 2012
9,694
Sounds like a short across the 350V ht supply, check on ohms ( supply disconnected)!! across the input and output of the bridge rectifier V11, C2,3,4.
 

Thread Starter

Melker.Jonsson

Joined Sep 1, 2018
6
shortbus,
1. Cooling fan removed.
2. Rectifier diodes (V11) are tested and is working as it should. V28,29,26,27 is also tested and is working.
3. Primary circuit power semiconductor. I guess this is the R30 and R23. Ive measured them both to 150 ohms at room temperature.
im not 100% sure whats the easiest way to test the IGBT's without desoldering every single one of them.

One thing i noticed is that when i had V11, C2, C3, C4, V7, V3, V1, V2 desoldered and measured between gnd and the collector side of V4 i got a reading of 0.1 ohms. Is that correct? Would my reading walk through the transistors, through the transformer primary and through V8 to gnd?

Therefore i could try desolder X13 and se if i now get power to v4, v5, v6

A bit messy text hope you understand what i mean.

Thanks for the replies guys!
 

shortbus

Joined Sep 30, 2009
8,060
3. Primary circuit power semiconductor. I guess this is the R30 and R23. Ive measured them both to 150 ohms at room temperature.

I would think that those, R23, R30, are resistors, not semi conductors. I think the semiconductors they mean are the ones marked V4, V5, V6, V8, V9 and V10, the IGBTs
 

shortbus

Joined Sep 30, 2009
8,060
Solved it V6 and V8 broken, collector shorted with emitter :) thanks for the help guys
R23 and R30 are PTC Thermistors btw
Did you read the last page of the manual? It recommends that when one of those goes bad all of them in that group should be replaced at the same time. So that means all 6 of them need replaced, since you have one in each group.
 
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