Lincoln 350c tripping circuit breaker

[mike 109444]

Was typing a reply then realized I had typed the same in post 27! So....
The AUX transformer is the small transformer (looks about 6" square) just behind the yellow three terminal choc block where the L3,L2,L1 go in.
There is a thin blue wire (and possible black) on left side that looks to feed 24v ac? to the fan. It will have an input to it! (maybe 240V from one of the 3 phases). It may also have other outputs for the low AC voltage going to the bridge in the pcb box. You should find on the bridge there are two AC input terminals marked with "~" and a terminal marked "+" and one marked "-". If you meter the inputs you should have between 24 to 30 vAC. Then on the +&- outputs you should see a similar DC voltage. Unless these voltages are very much higher or LOWER then that part of the AUX transformer is ok.
Re check what's in the bold.
It's the Aux that provides the power to pcb

 

[mike 109444]

Ps the AC in to bridge is on the YELLOW and GREY wires (meter set to AC volts) If ok then
SET METER TO DC volts and then meter the output on the BROWN and RED/WHITE.

 

[jimsbeast]

Hi mike thanks for your clear instructions, ive done this and the AC inputs read 38.5 and the DC outputs give me a reading of 53. (Readings from the bridge). How do these figures sound to you? I also get 56 where the terminals enter the pc board If the readings are slightly high/low is this enough for the pc board to decide not to work? Thanks again. James

 

[jimsbeast]

If i take a reading from the pcboard torch terminals, i get 15 when i pull the trigger that drops to zero, so i know the signal is getting from the torch to the pc board. Thanks. James

 

[mike 109444]

Hi James. I have had a closer look at the diagram and now see that the AC to the bridge is marked (on the aux transformer) as 42vAC not the 24 to 30 I first said! So your reading of 38.5 vAC although a bit low should be ok (this could just be down to the meter you are using ) The DC output of he bridge at 53 vDC would be about right for 38 AC in. As mot bit on the pcb would operate from 5vDC and 12 vDC then there is/should be voltage regulation/control going on on the pcb to convert the 53 to usable voltage levels.
Having yet again gone back through the previous posts it seams that the contactor is still not being operated by the pcb.
One way to confirm that the contactor is working and not faulty (FIRST UNPLUG WELDER) would be to disconnect the BLACK wire at the contactor (put some tape round the end to stop it shorting while you work on it) Then connect a length of wire to where the original wire went on the contactor and with a bit of the other end of this wire and the power back on, briefly touch it into the spade connector of the BROWN wire on the bridge rectifier by pcb. This SHOULD operate the contactor each time the wire is dabbed on the spade. Which will prove the contactor as being ok (It may have failed when it was being operated all the time with the original fault).
What is the history of the REPLACEMENT pcb you have fitted ? New, Used ?? Refurbished ?

 

[jimsbeast]

Hi mike will have a go at this tomorrow, the new pcb was brand new! From rapid welding supplies, who deal in lincoln parts. They were very helpful with selling the unit, but not been helpful at all with advice on repairing my welder ive called them i think 3 times and each time they said they would call me back but never did, pretty annoying you cant get the advice after spending a lot of money buying their part, ive stil got my old pcb i could re fit it to see what happens but i think the welder is acting exactly the same. But i will test the contactor out tomorrow if i get time thanks!

 

[mike 109444]

Hi mike will have a go at this tomorrow, the new pcb was brand new! From rapid welding supplies, who deal in lincoln parts. They were very helpful with selling the unit, but not been helpful at all with advice on repairing my welder ive called them i think 3 times and each time they said they would call me back but never did, pretty annoying you cant get the advice after spending a lot of money buying their part, ive stil got my old pcb i could re fit it to see what happens but i think the welder is acting exactly the same. But i will test the contactor out tomorrow if i get time thanks!

That does sound like poor support from them.
Sorry it's taking so long to get to the bottom of this fault but it can be difficult to do remote diagnostics safety.
I have to do and receive a fair bit of over the phone diags with colleges and know it might be one thing to know what you need to check but another to get that across on the phone!

 

[jimsbeast]

Hi mike thanks again for your help the contactor works fine when i do like you said clicks in and out everytime i touch the brown wire, im wondering if the other pc board can control the main pc board in this situation, with nothing at all operating when i pull the trigger its like something big is stopping the main board from operating all the individual parts (contactor, gas, wirefeed etc). I cAnt tell from the wiring diagram if the other pc board communicates with the main board in this way maybe you can? I cant imagine what else this problem could be. But im loathed to fork out more money to replace that board unless im sure this time, ive had a very good look at it and cant see any burn marks cracks or anything else that other pc board to suggest a problem.

 

[mike 109444]

There are links between the two boards. The display pcb is connected to the other pcb via X2/16 and X 2/7 also the over temp is linked to it via X2/15. Also the welding voltage is feed (sampled?) at B1 + and - and input to display pcb at X2/4 and 2/14. This is not to say that the display pcb is faulty but they must work together to control machine. The power (AC voltage) from the AUX transformer is also input/shared with the display pcb.
looking back at post 10 you said that the welder acts as though you are welding but does not feed wire. Does that mean if you had pull some wire through and operated trigger it would have melted the wire as though welding but not feeding any more wire to continue welding? (hope that makes sense). It that is correct does this new board allow the same ? (may not as the contactor is not being operated.
You might want to try refitting the original pcb as it should not take long and that would show if most of the machine is working.
If you can get a nice clear pic of one of the main pcbs (as you now have two!) can you post that up.
The headache is that most manufactures don't make detailed info of the pcbs available to non authorized repairers. The schematic in the manual is a lot more detailed than most others!!

 

[jimsbeast]

I will get photos up asap thanks again.
In short my problems have been like this...

A). To start with as soon as i turned the welder on the contactor would click in (and i could weld without pulling the trigger (although the wire feed and gas didnt work))

B). Then after a few days this stopped and nothing would happen at all

C). Then i fitted a new pc board (and nothing happens at all same as 'B')

I will swap the pc boards over again but as far as im aware they are acting just the same as each other

Part of my problem is the welder is kept at my workplace and i dont get much time to fix it only when im quiet in the week hence my sporadic replys but again tour help is much apprechiated. James

 

[mike 109444]

I will get photos up asap thanks again.
In short my problems have been like this...

A). To start with as soon as i turned the welder on the contactor would click in (and i could weld without pulling the trigger (although the wire feed and gas didnt work))

B). Then after a few days this stopped and nothing would happen at all

C). Then i fitted a new pc board (and nothing happens at all same as 'B')

I will swap the pc boards over again but as far as im aware they are acting just the same as each other

Part of my problem is the welder is kept at my workplace and i dont get much time to fix it only when im quiet in the week hence my sporadic replys but again tour help is much apprechiated. James

Not a problem James. As and when you get the time.
I'm not always able to get on net with a good connection as sometimes stopping out at hotels, at least Premier Inn now have free wi fi for more that 30mins !
Working for next fortnight at Barnstaple. Would be nice to be here when the sun is shining !!

 

[jimsbeast]

Hi mike, still no warmer here yet! Ive taken photos of the two pc boards and today i swapped the boards and re fitted the old board, it acted exactly the same as the new one and nothing worked, but there was one difference, with the old board the overheating light is on, on the front of the welder all the time..... Not sure if this gives u any clues on what i could try next Thanks again. James

 

[mike 109444]

Below is taken from the manual, page A2
I wonder if there is a faulty temp sensor (THERE ARE 3!) or false "temp to high" signal and this is causing the shut down of the control that the trigger should have.
Will look through diagram to figure tests

Duty cycle and Overheating

The duty cycle of a welding machine is the percentage of
time in a 10 minute cycle at which the welder can
operate the machine at rated welding current.
Example: 60% duty cycle:
Welding for 6 minutes. Break for 4 minutes.
Excessive extension of the duty cycle will cause the
thermal protection circuit to activate.
The welding transformer in the machine is protected
from overheating by a thermostat. When the machine is
overheated the output of the machine will turn “OFF“,
and the Thermal Indicator Light will turn “ON“. When the
machine has cooled to a safe temperature the Thermal
Indicator Light will go out and the machine may resume
normal operation. Note: For safety reasons the machine
will not come out of thermal shutdown if the trigger on
the welding gun has not been released.

 

[mike 109444]

Jim With the welder unplugged from the mains, pull the J1 plug off the board then with meter set to Ohms, meter on this plug (not the socket on the pcb!) between the pin 16 (green wire) and pin 6 (white wire) this should show as a dead short (00.00 on meter) may show a small amount. If you get an open circuit then one of the three temperature sensor/cutouts is stuck open. IF it is open then follow the green and white wires. They will go to a connector that should be labeled X14. From this, the wires may change colour but should form a loop going round to the diode pack heat sink + main transformer + the inductor (will look a bit like a transformer) then back to X14. Looking at the pic in post number 1 at the bottom on the transformer there is what looks like a pair of thin white wires going to a device that is mounted onto the windings. This MAYBE one of the temp sensors/cutouts.

 

[jimsbeast]

Hi mike thanks for your detailed response, ive done this test on the machine and the meter does go down to zero every time so i guess this indicated a closed circuit which is ok? Your right the green and yellow wires go into two small white wires which go down into the main gubbins at the bottom, is there any other way i can check or test these wires or temp sensors? Thanks as always. James

 

[mike 109444]

The metering of the thermal cut outs looks ok indicating they are ok. Only thing I can suggest would be to try shorting with a length of wire between the pin 1 and 2 of X 14. This will totally bypass the cut outs. This is the last thing I can suggest to do as remote diagnostics. Don't think it will sort though.
Another thing would be to go right through all the areas that you have had to check/unplug/meter looking for any connections that are not connected (remember the red connection on the bridge rectifier!) Unless someone has any other input then could be time for repair shop....Doh
You could print off this post to take along to assist the repairers with the checking.

 

[jimsbeast]

Hi mike, thanks again i will have a go at shorting the cut outs later, just wondering who would be best to look at this machine its difficult to take it anywhere as its so damn big i need like a mobile repairer or electrician! Thanks again. James

 

[mike 109444]

I would have no ideal who you could take it to. Hopefully someone will notice this post and recommend a shop or repairer near to your location. Is it not possible to go to the supplier of the pcb ?

 

[jimsbeast]

Hi mike, today i called some nice people at shropshire welding supplies the guy was very helpful and suggested a few things i could try, once i explained to him id tried everything under the sun he said ok and they are going to come out and look at it, maybe pick it up too so hopefully we will get to the bottom of it, wish i hadnt have fitted a new pcboard now but you live and learn i guess, i will let u know how i get on thanks again very much for all your imput ive certainly learnt a great deal more about welding machines the last few weeks! James

 

[mike 109444]

I'll keep my fingers crossed for you.
If the original pcb turns out to be ok then see if they may take the new one as part payment ? Worth a try.
It would be nice to find out the cause.
It's also nice to see you have "learnt a great deal more about welding machines" !
Every days a learning day