Help needed, faulty circuit on Clarke Pro-90

[mini670]

Hi, Im hoping someone can help me with my faulty welder.

Yesterday my Clarke pro-90 was working fine, id done about 6 inches of weld on my car. I the picked the welder up to move round to the other side, put it down. There was nothing, no wire feed, no arc, but the light on the power switch was still on.

I then had a look inside and removed the PCB. I have found that there is no continuity or resistance on the primary windings on the PCB mounted transformer. The secondary windings have continuity and resistance.

Im wondering if anyone knows how i can put this right, either with a new transformer, or a new board?

Any advice would be great!

Ta

 

[piman]

Hello Mini670,

you have nothing to lose by removing the transformer and seeing if you can locate and repair the break, my guess would be where it is soldered to the board? If not, then look for a compatible transformer? RS seem to carry a range of small transformers, ;-http://uk.rs-online.com/web/home.html

Alec

 

[mini670]

Cheers,

Ill have a go at removing it, and checking from there.

Thanks for the link to RS , they do have some tranformers that look like they might do the trick.
Ill let you know how i get on.

ta

 

[deltabravo]

Hello Mini, if the transformer is semi sealed,i.e. covered with insulation/tape etc, is there a slight bulge on one side of the transformer?, if so it is probably a thermal fuse. If you very,very carefully cut/strip the covering away it will reveal a small plastic block with a wire at each end of it. Inside the plastic block is a fuse which has gone open circuit. you can test it by wiring a link across the block to each wire, thus shorting out the fuse. If the secondary now shows voltage its job done, read the rating of the fuse on the side of the plastic block and replace with a similar item. Hope this helps, Bob.

 

[madkayaker]

Sounds like dead transformer you will need to know what the output voltage should be next problem is why did it go there might be a fault on board

 

[mini670]

Thankyou for your replies.

Today I have removed the knackered transformer and replaced it with a similar unit. I am now getting 24v to the board.

Though there is still nothing at all. Now am i right in thinking that the 24v output can be either way round, since its AC, or is it polarity dependant? If this does not matter, is there anything else I should be checking.

I also removed the cover from the PCB mounted relay, and the contacts closed. This results in an arc, but still no wire feed.


Any help appriciated as always

 

[mini670]

Sounds like dead transformer you will need to know what the output voltage should be next problem is why did it go there might be a fault on board

Im presuming it is 24v ouput, as the replay has 24v DC coil? Unless there is a circuit to knock AC output down to 24v DC?

 

[mini670]

Hello Mini, if the transformer is semi sealed,i.e. covered with insulation/tape etc, is there a slight bulge on one side of the transformer?, if so it is probably a thermal fuse. If you very,very carefully cut/strip the covering away it will reveal a small plastic block with a wire at each end of it. Inside the plastic block is a fuse which has gone open circuit. you can test it by wiring a link across the block to each wire, thus shorting out the fuse. If the secondary now shows voltage its job done, read the rating of the fuse on the side of the plastic block and replace with a similar item. Hope this helps, Bob.

Ive had a look at the transformer> there is no evidence of a thermal fuse. Once i removed it from the board, and removed the bottom plastic shield, inside was just the windings.

 

[the snooper]

you are right ac is not polarity dependant, have you checked the rectifier on the pcb and any diodes, sounds like you may just have to work through the components to check them .
before you go mad on it i would aim to get the relay working from the trigger as it will be the most simple circuit to diagnose then the wire feed may work anyway

 

[mini670]

you are right ac is not polarity dependant, have you checked the rectifier on the pcb and any diodes, sounds like you may just have to work through the components to check them .
before you go mad on it i would aim to get the relay working from the trigger as it will be the most simple circuit to diagnose then the wire feed may work anyway

Cheers,

Im unsure how to check the rectifier, and even which component it is. I know what resistors, caps, diodes , transistors look like, but cant decided on the rectifier circuit. It seems the wire feed is incorprated to loads of circuit i dont understand.
The switch is working on the trigger to PCB, as i checked continuity.

 

[mini670]

a couple of circuit board photos

 

[the snooper]

did you gaet a transformer with the same amount of solder connections on it ?

 

[mini670]

yea checked ins and outs its identical, putting 24v down onto the two rails on the board.

Im wondering now if maybe it should be more than 24v?

 

[the snooper]

from your pic it looks like you have de-soldered the diode next to the capacitor and trimmer did you pit it back in the correct way round

 

[mini670]

from your pic it looks like you have de-soldered the diode next to the capacitor and trimmer did you pit it back in the correct way round

When i recived the welder in was non-working. I went round the board with continuity mode on, it turned out to be a dry joint. Thats from sorting that out, done yards of weld since i did that. Other marks are just remelded soldier recently just to double check for other dry joints

also a quick photo of how the transformer is wired in

 

[the snooper]

from your picture of the board there doesnt seem to be a bridge rectifier instead they have just used the diodes so check that they operate correctly.
is it also possible to post a better pic of the top half rear of the pcb

 

[mini670]

from your picture of the board there doesnt seem to be a bridge rectifier instead they have just used the diodes so check that they operate correctly.
is it also possible to post a better pic of the top half rear of the pcb

Cheers.

Ill get a better photo aye, cant get down tonight, im in need of much kip

My meter has a diode check mode, does the value displayed show bias, and how do i tell if its correct?

Also bits on the board im usure of type/category are the two white blocks, the component on the heatsink, and the long white block near the switch connections. Threre is also a transistor along side the heat sank component, but unsure how to check?

 

[the snooper]

all you need for a simple check is a continuity a diode should only pass current in one direction this is how it turns altenating current into direct current .
pin 1 and 5 should also operate the relay.
pin 1 should connect straight to the switch on the torrch pin 5 should connect to the positive welding feed to the torch.
you will also need to check the welding rectifier inside the machine its the one with the aluminium heat sinks this should have 4 diodes on it and need to be checked the same way as mentioned above you may have to isolate each diode to get a true reading only go to that trouble if you get a circuit in both directions.

ps dont need the photo now have had a look at a wiring diagram

 

[the snooper]

just read your first post again and you mention the light on the power switch is on is it usually on as the circuit diagram shows that light as a warning that the thermal cut out has operated

 

[mini670]

all you need for a simple check is a continuity a diode should only pass current in one direction this is how it turns altenating current into direct current .
pin 1 and 5 should also operate the relay.
pin 1 should connect straight to the switch on the torrch pin 5 should connect to the positive welding feed to the torch.
you will also need to check the welding rectifier inside the machine its the one with the aluminium heat sinks this should have 4 diodes on it and need to be checked the same way as mentioned above you may have to isolate each diode to get a true reading only go to that trouble if you get a circuit in both directions.

ps dont need the photo now have had a look at a wiring diagram

Cheers mate i appriciate your help and time

I downloaded the Clarke circuit diagram, but caould hardly make sense of it, due to crap quality, and not showing all PCB components.

yea 1 and 5 make when trigger is pressed. I looked at diodes on the alloy plates, im getting a value of 411 on each side on either diode.
I checked all diodes on board got readings that i cannot recall now, but nothing in the reverse direction.

I gotta get to bed, even though this is really playing on my mind. Ill have another look tomorrow and post some info back if thats ok.

Ta