That's interesting, don't suppose you can see that step down on this board can you?Sealey liked to change the design of that pcb regularly, I had the same problem as you on my Supermig 180/2 & I couldn't find a photo or diagram online of a matching pcb. I traced the problem to the mini step down transformer on the board & replaced that.
Regarding running gasless wire, there's a thread somewhere on here about somebody trying to run gasless wire on a welder not designed for it (maybe a Sealey?). They tried swapping the polarity but that caused some issues (I think the feed motor ran backwards).
Thank you Hutcho. That makes R12 a 100 Ohm resistor, with 5% tolerance. The purpose is to bias the transistor "off" when there is no input signal turning it on. It seems like a very low resistance value for this purpose, I would expect from 1K to 10k, but even the burnt resistor is reading 99 Ohms, so it must be right....?Gold brown black brown
Thank you Hutcho. That makes R12 a 100 Ohm resistor, with 5% tolerance. The purpose is to bias the transistor "off" when there is no input signal turning it on. It seems like a very low resistance value for this purpose, I would expect from 1K to 10k, but even the burnt resistor is reading 99 Ohms, so it must be right....?
@Hutcho , if R12 is as low as 100 Ohms, it will show that reading, or slightly less, even when measured in-circuit on the board with other components in parallel with it, so if you get the chance, could you please measure yours to confirm the value?
The BUV46 transistor appears to be very broken. The Base to Emitter is open-circuit both ways, and the Base to Collector is short-circuit both ways, so it will have to be replaced with a new one. They are readily available in the UK :
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BUV46 x2 NPN SILICON TRANSISTOR TO220 400V 6A 85W Microelectronics VINTAGE | eBay
2 Pcs BUV46 NPN SILICON TRANSISTOR, CASE TO-220. Vce 400V, Ic 6A, Power 85W. Made by ST Microelectronics.www.ebay.co.uk![]()
If you test a component in-circuit and it shows the expected result ( e.g. a resistor value that is about right, a capacitor that is not short-circuit, or a diode that conducts one way and is open-circuit the other way ) then it can be assumed to be OK. If the result is wrong, it may the due to failure or because of other components in parallel, so then you would have to unsolder one end - or two/all for a transistor - and test again.Is there any other parts of the circuit or componants I should be looking at ?
I've tested all diodes and they all seem ok, although not sure how reliable it is to do that while they're in the board..?
Thanks Eddie, I've tested just about everything on the board now in situ and can't see anything majorly wrong.. From what I've read this looks like a pwm motor controller with what looks like an H-bridge, would that be a good guess do you think? I'm waiting on the parts from ebay which should be here next week and will update..I hoping for the best and expecting the worst ..!If you test a component in-circuit and it shows the expected result ( e.g. a resistor value that is about right, a capacitor that is not short-circuit, or a diode that conducts one way and is open-circuit the other way ) then it can be assumed to be OK. If the result is wrong, it may the due to failure or because of other components in parallel, so then you would have to unsolder one end - or two/all for a transistor - and test again.
The BUV46 transistor has definitely failed, and that has damaged resistor R12. Driving the wirefeed motor, that transistor has a tough life, and maybe it just died. However, it is possible that other faulty components earlier in the circuit sent too much Base current to that transistor, forcing it too hard into conduction, exceeding the power limit for the device, and causing it to short-circuit internally. There is a small chance that the new transistor may fail again.