Snapon Promig 160 trouble shooting

[Banstead2021]

Hi all,
Just joined so go easy on me. I’ve been searching through the threads to see if I can find anything to help me out. Basically I’m new to Mig and have picked up a Snapon ProMig 160 last night which has no spark.
I think I’ve tested the basics in that I’ve tested the secondary side of the transformer to the rectifier and get between 19-32V AC ish as I change the selector switch. From the rectifier outputs to the choke and earth clamp I’m not really getting any DC Volts when I pull the trigger, well I was seeing about 0..1/0.2V. So I pulled the rectifier out and tested each diode and was getting fairly consistent open circuit one side and around 0.5V on the reverse. So on the surface they all looked as they should.
Any help on where to go next. I’ve got a multimeter to test with that’s about it.
Am I looking at a duff rectifier? It appears that the welder is a rebadged cebora auto star, struggling to find any circuit diagram for this either.
Any positive help appreciated....who can help me bring this old girl back to life?
Thanks.

 

[the snooper]

Hi are you getting ac into the rectifier when you pull the trigger, also check any crimped connections, ie to the torch, welding clamp both from rectifier and torch end, just because they look good doesn't mean they are
edit, just re read it and you're getting voltage into rectifier

 

[Banstead2021]

Thanks for a quick reply. I’ve just checked and yes the rectifier gets AC from 20V through to 32V as the selector switch is changed and the trigger is pushed. I’ve checked continuity and zero ohms from the output of the rectifier to the torch tip. And also from the rectifier to the ground clamp and same there.
ive read the voltage across the DC output from the rectifier and I’m getting about 0.2V. Have I got a busy rectifier? Or am I missing something?

 

[the snooper]

Sounds like your rectifier if you have voltage in but nothing out, did you use the diode setting for testing

 

[the snooper]

If your diodes are testing good, remove the rectifier and clean all connections and try again

 

[Banstead2021]

So just took the rectifier apart and give it a good clean. Reinstalled and nothing still. I’ve taken the readings from each selector switch position at the rectifier and these are as follows:
1) AC 20V and DC 0.11V
2) AC 22.1V and DC 0.17V
3) AC 23.7V and DC 0.25V
4) AC 26.1V and DC 0.12V
5) AC 29.5V and DC 0.23V
6) AC 32.5V and DC 0.4V
So is it reasonable to conclude my rectifier isn’t doing what it’s supposed to do give the AC side appears to behaving? Should I do anything else?
Looking forward to your answers.
Thanks

 

[the snooper]

Well certainly looks like rectifier is at fault, test it with another ac low voltage power source, if you still get nothing you've found your fault

 

[Seadog]

Do you have a diode test position on your meter? If so you can check each diode in forward and reverse polarity. One direction should give a reading around 0.5 to 0.7 and I'm reverse, O or OL.

 

[Banstead2021]

Hi seadog, yes I’ve done that on them all and get 0.5 on each and open on the other. I can’t seem to find anything jumping out as faulty on the rectifier. I’ve stripped it down cleaned and reinstalled and still the same.

 

[DSR]

What voltage reading to you get if you connect your meter across the blue VDR and pull the trigger ?

I'd also try measuring the output of the rectifier on the AC range and see if you get something other than 0. 0 is expected, anything else could indicate the rectifier isn't :-)

 

[the snooper]

There has to be some reason for this, you get ac voltage and diodes check out, not buzzing badly is it

 

[Banstead2021]

What voltage reading to you get if you connect your meter across the blue VDR and pull the trigger ?

I'd also try measuring the output of the rectifier on the AC range and see if you get something other than 0. 0 is expected, anything else could indicate the rectifier isn't :-)

When you say the VDR do you mean the Varistor? If so that was 6.5V AC.

 

[Seadog]

In which case it must be poor contact. If all diodes measure OK and you have 20+ volts at the AC terminals, then you must be able to measure 36+ volts DC at the + and - terminals with nothing else connected.

 

[Banstead2021]

There has to be some reason for this, you get ac voltage and diodes check out, not buzzing badly is it

Seems ok. Just the normal hum when you pull the trigger.

 

[eddie49]

Try disconnecting one of the rectifier output wires and check for DC out again, so that you are measuring "off load".
Are you sure that the rectifier has been assembled ( or re-assembled ) correctly? In your first photograph, one of the output metal "ears", with a red wire on it, is bolted to one of the two rectifier mounting studs, on top of the white ceramic insulator. This is not normally a connection point.

 

[Banstead2021]

Eddie you beauty! So I cleaned and re-assembled the rectifier earlier based on how I got the unit. I’ve just swapped the +ve to below the ceramic insulator to contact the plate. Now I’m getting voltage. See pic. So from what I’ve seen the varistor looks like it’s in the wrong place. Should this contact both plates?

 

[DSR]

When you say the VDR do you mean the Varistor? If so that was 6.5V AC.

VDR = Voltage Dependent Resistor AKA Varistor

What was the voltage on the the DC range across the VDR ?

It does look more as if you have the output wires connected to the wrong points in the rectifier as eddie49 mentioned.

 

[Banstead2021]

it’s currently connected to the AC side and then above the top ceramic? Should it be to both plates?

 

[DSR]

Eddie you beauty! So I cleaned and re-assembled the rectifier earlier based on how I got the unit. I’ve just swapped the +ve to below the ceramic insulator to contact the plate. Now I’m getting voltage. See pic. So from what I’ve seen the varistor looks like it’s in the wrong place. Should this contact both plates?

No, the varistor is in the right place - it's across the expected DC output of the rectifier. The heavy duty cabled to the earth clamp and torch should be connected to the same plates as the VDR. Do a resistance check you you should have 0 ohms from one end of the varistor to the earth clamp and 0 ohms from the opposit end to the torch.

 

[Banstead2021]

No, the varistor is in the right place - it's across the expected DC output of the rectifier. The heavy duty cabled to the earth clamp and torch should be connected to the same plates as the VDR. Do a resistance check you you should have 0 ohms from one end of the varistor to the earth clamp and 0 ohms from the opposit end to the torch.