Anyone with vintage migatronic knowledge? Laggy wirefeed issue on mono 200

[Gareth J]

Migatronic mono 200, 1980s machine.

After a few trigger presses/a bit of use, if you pull the trigger quickly after the previous weld, the wire feed doesn't start immediately but lags a bit. This doesn't happen every time but does happen more or less repeatably.

As per this;

I thought it could be a residual voltage issue, as that takes a while to sag down, but it's not repeatable based on voltage, it's related to time. After about 5seconds, the wire feed starts immediately as expected.

Have ruled out actual motor/brushes/relay issues as with the weld mode switched to "latching", where one trigger pull starts the weld and a second stops it (all the mod cons on this cutting edge machine!) it works perfectly, no matter how rapidly you fire it on/off.

Which points to a circuitry issue??

Which although it looks very simple by modern standards, still represents a more complicated and time consuming avenue than I can get involved with.

Otherwise, it welds lovely and would like to keep it. But don't have a lot of time to put to repair work.

Current workaround is to use in latching mode and try to get used to that. But anyone with ideas, experience or repairer contacts, I'd be grateful to hear.

 

[BrokenBiker]

Dodgy joint thats getting hot with use?

 

[Gareth J]

Thanks for that, I just replaced both burnback and wirefeed pots. The wirefeed was definitely duff - it had been degrading slowly and I hadn't realised just how rubbish the machine was welding. Still not sure if the burnback does anything but it doesn't really matter.

Good idea with the on/off switch. I just use the wall switch but if that wasn't an option, rolling the main one round the steps would be tedious.

Thanks for the help

It looks like 5 years ago, I replaced the wire feed potentiometer. Zero recollection of that, which is a bit worrying. Especially as I wrote about it. I don't think it's that.

 

[BrokenBiker]

It looks like 5 years ago, I replaced the wire feed potentiometer. Zero recollection of that, which is a bit worrying. Especially as I wrote about it. I don't think it's that.

Ok...so maybe a joint getting hot with use?

 

[Gareth J]

Dodgy joint thats getting hot with use?

Maybe. But hard to see how, if changing the 4 position switch for the weld mode cures it....unless the location for normal welding on that 4 position switch has degraded...

 

[BrokenBiker]

Maybe. But hard to see how, if changing the 4 position switch for the weld mode cures it....unless the location for normal welding on that 4 position switch has degraded...

If changing modes cures it, the fault lies within the circuit for the mode that isnt working correctly, so that eliminates 3/4 things...I'd be looking at all wiring, switches, joints and parts of the board that relate to that specific mode...if its fine when left for a while, it would indicate some form of heat building up somewhere, or a joint opening up, broken wire opening up, switch contacts failing etc

 

[Gareth J]

I'm now not sure if changing the settings does cure the issue. It may be perception that it does because you're forced into delaying a restart.

Have not managed to find anything loose yet. Been wriggling wires and tightening connectors.

 

[BrokenBiker]

I'm now not sure if changing the settings does cure the issue. It may be perception that it does because you're forced into delaying a restart.

Have not managed to find anything loose yet. Been wriggling wires and tightening connectors.

I was thinking more towards a soldered joint or broken wire than a screw type connector.

Ideally you need to determine if it is only on the 1 mode or if all are effected

 

[Gareth J]

Just checked and it's not just the one mode as I initially thought.

I wonder if there's a relay that's involved with wire feeding that takes a second or two to release somewhere.

 

[mike 109444]

Is the wire feed motor a 2 or 4 wire motor ?

 

[mike 109444]

It could be, not that the wire feed motor is slow/delayed in starting but more that the "braking" for the motor is failing to disengage (fully).

 

[Gareth J]

Is the wire feed motor a 2 or 4 wire motor ?

4 wire.

It could be, not that the wire feed motor is slow/delayed in starting but more that the "braking" for the motor is failing to disengage (fully).

Sounds plausible, if I were to disconnect one of the brake wires, so it ran on, maybe I could confirm/disprove the idea that way.

 

[Robotstar5]

4 wire.

Sounds plausible, if I were to disconnect one of the brake wires, so it ran on, maybe I could confirm/disprove the idea that way.

Brakes on those are normally "fail safe" so disconnecting a wire will cause the brake to stay on.

 

[Gareth J]

Brakes on those are normally "fail safe" so disconnecting a wire will cause the brake to stay on.

Well, disconnecting each motor wire in turn did not let the motor run.

Maybe some probing with a multimeter would be sensible.

 

[Robotstar5]

Well, disconnecting each motor wire in turn did not let the motor run.

Maybe some probing with a multimeter would be sensible.

Thinking about it, I have not come across a braked wire feed motor (happy to be proved wrong though) the second pair of wires are usually from a tacho to be fed back to the control board for speed control.

 

[Robotstar5]

A bit like this, the red & black wires are for the feed motor and the grey pair are tacho feed back.

 

[Gareth J]

AS may be very obvious, I'm stabbing in the dark a bit. I don't really know how it all works, how to properly diagnose or what that will mean after it has been diagnosed.

Am wondering if, as a backup solution, it's possible to buy replacement control circuitry for the wirefeed motor. The motor, gearbox and rollers themselves look alright and the transformer unit should be pretty robust. I don't need fancy control options.

 

[Dragnet]

I would clean all the switches as a matter of course. I use Servisol 10/Kontakt 10. Testing the motor by itself would rule out whether it's a problem with the motor starting and stopping rapidly. Have you tried another torch in case it's the torch switch? A motor relay could be failing to contact properly; an overheated electrolytic capacitor could be coupled to a resistor that's gone high and failing to discharge fast enough for some kind of timing circuit. I can see one tantalum capacitor and several epoxy-cased types that are likely PHE rather than paper - I only mention this as I'm currently replacing all the paper capacitors in a TIG box which are all cracked. Nothing blindingly obvious on your PCB in that photograph. Have you got a circuit diagram?

The advantage of these old machines is that they're repairable, but as you say you have to have the time, inclination and skill to repair them!

 

[Erie Fred]

There isn't a "soft start" setting ?

 

[Gareth J]

Have you tried another torch in case it's the torch switch?

The advantage of these old machines is that they're repairable, but as you say you have to have the time, inclination and skill to repair them!

I shorted the switch contacts on the connector block to rule out anything torch related. Same results.

Yeah hopefully repairable, but I'm pretty short on time. I did once replace a welder's wire feed power supply, which was successful. But I don't have that sort of time now. Or probably the skill requirements.

I've given it all a bit of a clean with a soft dry brush but will try the switches with some solvent electrical cleaner. Thanks.

Nothing blindingly obvious on your PCB in that photograph. Have you got a circuit diagram?

No diagram here. I could take a better photo if I pulled the board out a bit more. Which I did do earlier. I couldn't see anything obvious though.

There isn't a "soft start" setting ?

Don't think so, there's a "burn back" setting that changes the amount of time the gas stays on for after trigger is released. But little else wrt to settings. It's pretty old.