Eland mig 130 with issues

[a111r]

Good progress there.
I have had a similar 'step change' type fault like this ("welds lovely for 1" then goes splashy")

The cause was rectifier diode partial failure. The voltages can test to spec. fine, like yours did.
The diodes too, on the 9 volts from the DV meter's diode test function.
In operation, not so. Try heating the diodes with a hot air gun and then test them?

 

[GraemeVW]

Good progress there.
I have had a similar 'step change' type fault like this ("welds lovely for 1" then goes splashy")

The cause was rectifier diode partial failure. The voltages can test to spec. fine, like yours did.
The diodes too, on the 9 volts from the DV meter's diode test function.
In operation, not so. Try heating the diodes with a hot air gun and then test them?

I may just replace them all then if that's a possibility.

 

[GraemeVW]

Picked up some components on the way home and swapped all the diodes out. Changed the electrolytic caps too as they have a habbit of drying out over time.
Just waiting for the new transistor now.

Not my neatest work, but it will do.

Noticable how components get smaller! Diodes are smaller and the caps are smaller even though the voltage ratings are 50% higher!

The big one (main smoothing cap for the motor transistor?) Is a higher uf too as that's all the shop had. Shouldn't matter.

 

[GraemeVW]

The above photo isn't great, but if you look closely you will see the mistake made from new.










The fuse holder. One side was the wrong way round!

This ment that the little stops that stop the fuse sliding sideways were clamping the glass of the fuse before the holder touched the end cap . The end cap was still contacting, as it still worked, but it wasn't a good tight fit, just a bit of contact.
I just turned it round.
Probably not part of the issue, but shoddy!

 

[eddie49]

The BDX18 power transistor is a pretty beefy component, rated at 60 volts, 15 Amps, and 117 Watts. It is like a PNP version of the classic 2N3055, and would take a lot of abuse to burn it out. It is possible that one of the two red-cased relays is wired to brake the wirefeed motor to a dead stop by shorting it, and it may have accidentally overloaded the power transistor.
That PCB has a very impressive 16 diodes on it !
It may be worth overhauling the wirefeed motor: brushes, commutator, bearings, and gearbox lubrication could probably all benefit from a check-over.

 

[GraemeVW]

The BDX18 power transistor is a pretty beefy component, rated at 60 volts, 15 Amps, and 117 Watts. It is like a PNP version of the classic 2N3055, and would take a lot of abuse to burn it out. It is possible that one of the two red-cased relays is wired to brake the wirefeed motor to a dead stop by shorting it, and it may have accidentally overloaded the power transistor.
That PCB has a very impressive 16 diodes on it !
It may be worth overhauling the wirefeed motor: brushes, commutator, bearings, and gearbox lubrication could probably all benefit from a check-over.

Yes, feed motor and gearbox overhaul is next on my list.

Can you explain a little more about what you think may have overloaded the transistor? The way I read your post, I'm not sure if you think the motor may have, or the relay may have.

Thanks

 

[eddie49]

It depends on exactly how it is wired; you'd need to follow the tracks and reverse-engineer the diagram. Start at the two motor wires, they may both go to a double-pole/double throw relay, which connects them to either the power transistor or to a dead short. That should be foolproof. If there is a transistor that shorts the motor, it could conduct too early and short the supply. Maybe the BDX18 just got tired after 35 years and gave up.

 

[GraemeVW]

It depends on exactly how it is wired; you'd need to follow the tracks and reverse-engineer the diagram. Start at the two motor wires, they may both go to a double-pole/double throw relay, which connects them to either the power transistor or to a dead short. That should be foolproof. If there is a transistor that shorts the motor, it could conduct too early and short the supply. Maybe the BDX18 just got tired after 35 years and gave up.

It seemed to have slight motor speed stability issues, not enough to see in the drive, but enough to effect the weld. I'm hoping that was just a sign the transistor was about to fail.
I'll check the pcb more but I suspect the transistor just failed.
Only other parts I could change just in case are the relays themselves and the w small driver? transistors, but they all seem fine.

Just trying to cover my back so the new bdx18 doesn't just blow when I power it back up.

 

[eddie49]

Just trying to cover my back so the new bdx18 doesn't just blow when I power it back up.

For the initial power-up, replace the wirefeed motor with 2 x 12v 5W car side/tail bulbs in series.
The speed pot will then act as a dimmer, and the 0.4 A current draw should be safe for the power transistor.

 

[GraemeVW]

For the initial power-up, replace the wirefeed motor with 2 x 12v 5W car side/tail bulbs in series.
The speed pot will then act as a dimmer, and the 0.4 A current draw should be safe for the power transistor.

One thing I did notice was, checking power to the motor, it seemed to be 32v and the feed pot made no difference. Feed pot does vary the motor though, just didn't show up on the multimeter.

 

[eddie49]

The motor speed control circuit is probably pulse-width modulated ( PWM ). The pulses will be 32v, which gives full torque at all speeds, but their width will vary.

 

[GraemeVW]

The motor speed control circuit is probably pulse-width modulated ( PWM ). The pulses will be 32v, which gives full torque at all speeds, but their width will vary.

I thought it must be controlled some other way than voltage but don't know enough about electronics to know what the other options were.

Thanks.

 

[GraemeVW]

Opened the feed motor, it's like new in here!
No dust, brushes are perfect, com is spot on. No wear at all!
I was expecting to need to skim it but it's very good. I wiped the com with a cloth to get the carbon off. I'll clean it a little more and put it back together. Even the grease in the gearbox is like new.

As I suspected, this welder has done very little work!

 

[GraemeVW]

Fitted the new transistor and still no power to feed motor.
Took the pcb out, new transistor was already warm, but still tests ok.

Turns out the relay has broken. The white plastic part should move both reeds. As it sits, both sides of the contact are closed!

@eddie49 do you think that could have been what killed the transistor?
The contacts of the relay seem to switch between the transistor emitter and the positive motor terminal.

I'll see if I can order another relay, maybe just replace them both if the plastics getting fragile!

 

[eddie49]

the two motor wires may both go to a double-pole/double throw relay, which connects them to either the power transistor or to a dead short. That should be foolproof

With the relay armature frozen, and apparently both sets of contacts closed at the same time ( ? ), it's no longer foolproof.
Rather than the motor, the current passing through the large transistor is going to the motor braking circuit - which is usually either a low-value resistor or a dead short. That would explain why the poor transistor is getting warm!

 

[GraemeVW]

The right relays seem tricky to find. Popped to local shop to see what they had.
Wrong pin out and wrong pin location.
Quick bodge to swap over the normaly closed pin, should work.

If anyone is looking to employ someone to wire spaceships, guidance systems, or other intricate, critical systems, give me a shout.


Honestly, I can do better than that, just want to see if it works!

 

[GraemeVW]

With the relay armature frozen, and apparently both sets of contacts closed at the same time ( ? ), it's no longer foolproof.
Rather than the motor, the current passing through the large transistor is going to the motor braking circuit - which is usually either a low-value resistor or a dead short. That would explain why the poor transistor is getting warm!

I had a quick look at the tracks, I think it shorts to ground via a cap maybe, I gave up before I worked it out and ran to the shop for more relays.

 

[GraemeVW]

Was going to just replace one relay and see how it went, but the same plastic piece fell apart on the second relay while I was soldering the first!
These must have been properly on their last legs.
So, 2 new relays bodged on. I'll chuck it back in after dinner, see if it works now!
Can't be much left that can be wrong. Resistors all check out, the few caps I haven't changed are of types that should be fine. Just the 2 small transistors and the chip left.

Chip seems to be a timer, so I guess that deals with the pulse and spot functions. No idea if it's off the shelf, or programmed though.

 

[GraemeVW]

Put it back together and it's closer, but still no joy.

@eddie49 I may have to appeal to you for your thoughts, sounds like you understand these things and I've about run out of talent.

With the new relays fitted the motor still doesn't run. I do now have 32v at the motor terminals when I pull the trigger. Motor runs just fine if I power if from a bench psu.
What I'm hoping may mean something is when I pull the trigger I get high frequency noise from the transformer. This noise varies in pitch if I adjust the wire speed. I'm sure it didn't do that before.

I'm going to go back over the pcb, make sure I haven't made and silly mistakes, but I was very careful (and double checked) that everything went back as it was before.

The new relays both fire, and I'm 99% sure I got the switchover connections the right way round.

I'm puzzled now. Got voltage to motor, motor works, but no spinny.


Edit, been over the pcb and everything is as it should be, no diodes the wrong way round, relay switch overs are the same way round as the old ones were, all solder joints are good.

Edit 2, very small possibility I may have slightly unreliable contacts in the relays when tested without power, but they seem to work fine under power. One switches mains out (to contactor, or transformer, not checked) that works fine. The other shorts the motor connections at idle and then switches in the output from the transistor when fired. That works as I get voltage to the motor when I pull the trigger.

So their either must be no current, an issue with the pulse width modulation, or some other random fault I've no clue about.

Edit 3 took one of the new relays off the board, popped the top off, and the contacts are rubbish! Had to use a nail file to try and clean the contacts up to get them even remotely reliable. These finder relays are terrible.
Can't find the proper schrack ones.
Might try and find some better ones and put them on a separate pcb and wire it in remotely.
Still not convinced it's my main problem though.

 

[GraemeVW]

Found these images in an old post