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Dave's Build Thread
#41
Measure the resistance across the L and N pins to see if the fault is arcing or a firm low resistance. If the fuse has blown and not replaced, then measure after the fuse inside the case.

If it is a fixed low resistance the primary winding on the transformer may have overheated and shorted some of the windings, the failure mode may end up shorting out the switching circuit and leaving the transformer permanently connected. If the transformer was ok and there is no short on the secondary it should not use any significant power when switched on, but if the windings have fused it will end up as acting line a large inductor/heater. Does the transformer smell ?

One option (worst case no return to seller) disconnect / se-solder one of the primary windings to the transformer and measure the resistance. The secondary (weld side) should not really melt by the looks of the wiring thickness.

Also, power it up without the footpedal...

Another thing I have noticed with some EU rated equipment (220V) is that they can't cope with higher UK voltages, which may see 250V or more at the plug... This could add to the unit over heating with use or more normally the burning smell of burning capacitors followed by various fireworks....

The switching FET's may be on the other side of the front board.

Popped FET/TRIAC.... and repair
https://syonyk.blogspot.com/2015/05/sunk...epair.html
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#42
If you put a lamp eg a 100W or bigger incandescent in series with the mains lead, you can test with less fireworks :-)

The continuity you're seeing might be circuitry? Not sure if you doing this already but maybe test just the transformer by itself?

The mains side of a hefty transformer like this will measure low ohms with a meter normally & picking shorted windings might be tricky. You can buy transformer testers that look for shorted windings but that's spending $ ;-) Confirming it's arcing between windings, etc can be hard because it won't arc without mains voltage on it.
Running off solar, DIY & electronics fan :-)
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#43
The transformer appears fine. It could be arcing, but I can't see that. I'm pretty sure its the control circuit that's a fault here even though i can't see any obvious physical signs. There is definitely continuity between AC in and AC out when the unit power switch is switched on (with power off). Its not consistent though. Sometime no continuity. I think its when I handle the board, so maybe a trace failure somewhere? i don't know.

I'm thinking of making a switch to manually drive the transformer. If I can do that then i can verify the transformer works. After that is confirmed, i'll be replacing the circuitry. I think the arduino solution would be better than just buying a replacement original PCB. the only thing I don't like about it is that the settings are all digital. I really like having a manual dial for power.
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#44
Sounds like the board. Have a look at the link I added as they go through some of the failure issues people have had and the repairs. The board could just have a failed triac or other parts that are only visible on the other side of the PCB.

If the transformer was arcing or melted windings it would smell, so good there is no smell.

Desolder the transformer leads from the PCB and power it up - check the secondary is not shorted beforhand, should be open circuit (reading a low reistance of the windings).

Check the link out as a few of the responces had different modes of failure with some the triac blowing out and others with components being vapourised off the board.

At a guess the issue could be the transformer switching could not cope with the high voltage spikes when disconnecting the transformer full load at the peak of the waveform because the weld pulse timing is not syncronised to the incomming voltage waveform. Repeat switching with a higher supply voltage (UK houses typically see 250V) would then weaken the triac to fail early. Next time I use my welder I will have to put it on a very long extension lead to add a larger voltage drop under load....
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#45
(09-04-2018, 09:29 PM)completelycharged Wrote: Desolder the transformer leads from the PCB and power it up - check the secondary is not shorted beforhand, should be open circuit (reading a low reistance of the windings).

Good idea. I did this. The board powered up and stayed on. So I tested the Live out to the transformer. Its showing 80vac. 
80vac? Now that's weird right? 
So that's what's tripping the breaker. I don't know what on the board has failed. There really is nothing that looks burnt. The triac looks fine.
I'm probably going to get an arduino controller at some point. But In the meantime, i'm wondering if I could use the transformer manually to finish my welding.
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#46
80V for the spot welding secondary is far too high, so sounds like the transformer has some sort of issue.

Test if the primary and secondary are isolated. Extreme thought, the secondary and primary windings are joined somewhere in the transformer so the 80V is part secondary and like a tap off on an auto transformer. The only thing I can think of in order to get 80V. My understanding of the way the spot welder works is thatr the secondary is shorted across what you want to weld and the primary is pulsed (as an attempt not to blow the input fuse and regulate the input energy).

Might just be an issue with the transformer secondary, in which case it may be possible to take the winding out, cover it with tape and re-wind it back in as it should only be a few turns.

Also to check the board is working ok, if you have an oscilloscope it would help more, put the meter on the transformer connection points on the PCB before re-attaching the transformer to the PCB and activate the welder. The meter/scope should then display a very brief voltage reading if the board is fine.
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#47
The 80Vac is the supply to the transformer from the PCB. It the primary winding. Its a constant 80V (Actually, its 83V to be more accurate). It does not change when the weld switch is activated. The transformer is disconnected from the PCB, so its nothing to do with the transformer. Clearly something wrong with the PCB. It should allow AC to the primary winding, but only when the weld is initiated right?
Why would it supply anything at all to the primary when you are not welding? I don't think it should.
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#48
Ahhhhh... ok...

Yes, the output should be off and then pulsed on, so the triac is partly shorted out. Have you managed to get the board fully out of the case to see all sides of each of the chips ? On the odd occasion they vent out and have very very slight markings, or not...

If they are not showing any signs of damage check the input side to the triac to see if that is the same 80V or higher as it should be mains and then trace back from there if it is still 80V on the input.

This is one of the two FET's I just replaced in a MakeSkyeBlue MPPT controller I managed to blow by putting the PV in the wrong way round (wired one of the plugs wrong and did not tripple check...). Very small venting in only one of the two FETs..
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#49
I'm making slow progress on this due to 100% focus on getting a job at this time.
However, got some job application dead time, so I've had a look again at this welder.
I've read the Triac datasheet now too, which helps as i'm not great at electronics at all
Its:
T1 - power in.
T2 - power out.
Gate - the switch
With the power to the PCB off, i get continuity between T1 and T2 where I shouldn't. Its not zero resistance, but about 850/1000 on the multimeter. Ohms I suppose? I don't really know what its measuring. I had touched all pins with my finger to make sure is wasnt holding a charge too, so its not that.
I'm also seeing a resistance of 170 between T1 and Gate. I have no idea what that means, if its normal or not.

When powered on, I'm seeing:
T1 - 230V
T2 - 80V
Gate - 230V. (wtf?)

so i thought its pretty conclusive that the triac is fried. So I removed it. And guess what? I'm still getting 80V at T2 position on the PCB. Still 80V on the AC output to the transformer. However, its now 0V at the gate, where it was 230V at the gate with the triac in place. I have no idea where this 80V is coming from and at this stage, i'm going to cut my loss with this controller because I'm not able to make sense of where the traces go. The Trace from T2 doesn't appear to go anywhere! Its a double sided PCB, but I can't even see the path between the Triac output and the pinout to the transformer, let alone see where this 80V is coming from.
I also spotted one of the capacitors is hot. Hot to the touch where the other caps are not. It doesn't visually appear to be blown though. I suspect whatever component has failed has created a chain reaction of further failures.
So that's my best shot and it wasn't good enough!

Cheers very much for your help though - Its most appreciated Smile
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#50
Many circuits will pass a small current enough to read 80VAC on the meter if there's no other load, just the meter.
Try measuring the board output with a mains lamp in place of the transformer.

No cap should ever be too hot to touch.... something going on there for sure.

The PCB may be a four layer one (ie hidden layers in the middle)
completelycharged likes this post
Running off solar, DIY & electronics fan :-)
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