Sealy supermig 185 PCB repair help

[bikemech]

hi all, am new to the forum and looking for some help fixing a PCB on a sealy supermig 185, the welder is not mine and belongs to a friend, it seems to power up but the relays don't click when the trigger is pressed and there is no wire feed, he called sealy and they say it's the PCB,
Can anyone help me test and possibly repair this board, I have a multimeter and am an amateur in electronics, any help would be fantastic, here is a photo of the board, sorry for the quality,

Thanks,
Pete.

 

[mike 109444]

There is a 1.5 amp fuse that protects the low voltage transformer (looks like if blown the fan will also not run worth checking IF fan is still running!). if it is then check if there is 24vAC coming out of it. The above info is referring to the TC1 bottom left of diagram. Hope you are ok reading diagrams ?
And welcome BTW Pete

 

[Spark plug]

Could also be the connections at the torch or the switch in the torch.

 

[johnward]

hi....not 100% sure but it looks like c14 cap has died....the top looks blown out...

 

[the snooper]

hi....not 100% sure but it looks like c14 cap has died....the top looks blown out...

ive just zoomed in on that not sure if it is blown out or if its the white paint that's has been applied in a curve

 

[the snooper]

have you also checked that the relays are ok ?

 

[mike 109444]

Manual indicates it's a euro torch so should be easy to check.
Noted there is a thermal sensor on the L1 inductor which should operate the ST1 (?) and cut the machine out and light the TEMP light (HL1)

 

[Wedg1e]

1993? Brand new, that is!

ive just zoomed in on that not sure if it is blown out or if its the white paint that's has been applied in a curve

White paint? Is it not a reflection of light from the pressed-in cross on the end cap?

 

[Wedg1e]

If your multimeter has a diode check range you could test all the diodes and transistors on the board; you may get some confusing readings due to other components but you can usually spot an intact or duff semiconductor junction.

 

[bikemech]

Thanks for all the replys , am going to try test as much as I can later tonight, will start with he diodes and transistors, is there a schematic for this board anywhere, I can't find one!

 

[bikemech]

What are these and how do I test them please 2N3440?

 

[bikemech]

There is a 1.5 amp fuse that protects the low voltage transformer (looks like if blown the fan will also not run worth checking IF fan is still running!). if it is then check if there is 24vAC coming out of it. The above info is referring to the TC1 bottom left of diagram. Hope you are ok reading diagrams ?
And welcome BTW Pete

Hi and thanks, I can normally fumble my way through a diagram ok lol, I will check the 1.5A? Fuse later today, the 24v from TC1, it there only 2 leads to test from it, sorry but not actually been inside the machine yet, the owner did say he replaced a main fuse inside at the top! And the wire feed sometimes slowed on its own, once the machine cooled it went back to normal

 

[bikemech]

Had a quick look today, the 1.5a dues is the one he already replaced, the fan comes on when the unit it turned on just no wire feed !

 

[the snooper]

1993? Brand new, that is!


White paint? Is it not a reflection of light from the pressed-in cross on the end cap?

yep looks like you was spot on looking at latest picture

 

[mike 109444]

The 2N device is a transistor. (few bob to replace IF duff) Search ebay using the number and you should find them. What the other guys are pointing you to is the swelling of the capacitor C14 you should be able to see that the top has become domed. Sometimes they just pop. Note transistors don't give very good "in circuit" indications that they are faulty even if the reading you get seams to be a dead short a small capacitor can give that sort of reading.
You should be able to find the data sheets for most if not all the transistors on the pcb.
Most manufactures don't seam to make the schematics for "there" pcb available, why if they did that those chappys over in China would be churning out welders.....Wait a minute they are ........

 

[the snooper]

also its worth noting that if you decide to remove the transistors to test them, too much heat from the soldering iron will destroy them

 

[mike 109444]

ps a good and basic starting point would be to check for dry solder joints with a magnifying glass. in particular the wire feed control as it is used to mount the pcb on the front of the machine so the weight of the pcb is taken by the pots fixing to the pcb!

 

[bikemech]

C14 and all the caps are fine, think it's just the photo! Looked for dry joints and all look ok, I know I can get duff readings without removing some components , looks like I will have to remove the transistors find pinout for each and test each one then replace as and if needed, diodes all seem fine in circuit to,

 

[mike 109444]

Did yo rule out the torch ? using a paper clip or link of wire to short in the euro socket to emulate the trigger being pulled ?

 

[Wedg1e]

Just noticed the OP is on my doorstep

Had a quick look today, the 1.5a dues is the one he already replaced, the fan comes on when the unit it turned on just no wire feed !

Try poking 12V directly into the wire feed motor and see if it runs. Ideally use a current-limited supply (rather than, say, a car battery) and disconnect the motor from the PCB (oh wait, it already is ).

My guess is it uses the UC3842N IC to generate a variable pulse-width waveform for the driver device to control the motor speed; the driver could be the one with the heatsink attached, near the corner of the PCB. If the IC or the driver device have gone phut that'd be the problem - but equally it could be something simpler, say a dried-out electrolytic in the timing circuitry, especially on something that old. It wouldn't take long to trace the entire board and produce your own circuit diagram for it, then you'd have a starting point.

The 2N3440 is a 250V 1A NPN transistor, centre pin is Base and the pin nearest the tab is the Emitter...

http://pdf1.alldatasheet.com/datasheet-pdf/view/21682/STMICROELECTRONICS/2N3440.html