Transistor rusty

I hope this works.
I have been told this circuit in the manual is not the same as mine ???

Les,
am I right in saying if the transformer is re attached and wired in, switched on, should I have a 24v reading from the 2 blue wires on the secondary side. Correct ?

Transformer resistance test.
Is this right
RED meter probe on black wire
BLACK meter probe on yellow wire

READING WAS .657

RED meter wire on black wire
BLACK meter probe on red wire

READING WAS .981

resistance does this look right ?

Re post #22 You are correct. You should have 24 volts AC between the blue wires. NOTE the meter must be set to an AC voltage range. (If it is set to a DC range it would probably read about zero.) I added that comment as the fact you don't give any units you are not familiar with using a DMM.
Re post # 23 Assuming the units are K ohms the readings are about right. For 220 volts input it would be connected to the black and yellow wires. The red wire would not be connected to anything, (It may be connected to an unused terminal on a connection strip.)
The manual gives me an idea of the size of the unit we are dealing with.

Les.

Does the polarity matter when I connect the plug to the black and yellow wires to 240v ? To test 24v output ?

Polarity does not matter but be careful not to touch the red wire as this will be about 380 volts with respect to the black wire. Also make sure it does NOT make contact with the black or yellow wires. Make sure the blue wires do not short together.

Les.

Great thank you Les, just wanted to check before I try it.

Update
Good Afternoon.
I tested the DC welding output voltage.
Neg meter probe on the Dince earth side and the pos meter probe on the torch end tip.
Turned on 240v switch ( voltage dial set on (0) pressed the trigger and got a reading of 19.5v
Turned the voltage knob up to (1) got a reading of 25.1v
Turned voltage up to (3) got a voltage reading on 30.7v
And finally (4) read 39.6v
Hope these readings are OK.
Now
About the 240v-24v transformer.
I hooked the primary side yellow wire to the live 240v brown and then the red wire to 240v neutral.
Tested that it was reading 240v..
Tested the secondary side (the 2 blue wires) and got NO reading. Nothing at all.
Checked the primary was getting 240v again. Nothing from the secondary blue wires.

I take it the transformer is shot.


I just left the black wire that goes off to the big transformer. I didn't attach that to anything. I just left it attached.


I don't understand when the transformer is re attached I can hear the relays click and I can get a spark but with no wire feed obviously.
What's your thoughts please.

There is a "remote" possibility the 24V transformer has a built in thermal fuse. I've had on fail on me before. They are on the primary, and taped inside the yellow tape that goes around the primary winding. Theory is, if the transformer overheats, it cuts out, permanently. However, those fuses also seem to fail with age. Options are to either replace the transformer, or carefully unwrap the primary tape to find that thermal fuse. No guarantee your transformer has one however. WHat are the ohm readings on that transformer, both primary and secondary. Any blown winding will be infinite resistance.

For your relays to click, there has to be some voltage feeding them, from somewhere. See if you can find the 24VDC source for the relays on the board itself. Trace that back to verify which transformer is supplying that 24V. I suspect the AC is being rectified on the board itself, so once you trace back from relay to the diode, it will be AC voltages backwards from there. It must connect via one of those connectors.

Your tests seem to suggest that the transformer is faulty but I don't see how the relays can click without the 24 volts AC from the transformer. I suspect you may not be making contact between the ends of the blue wires with your meter probes. With no power to the welder measure the resistance between the blue wires. (The best way to connect to the ends of the blue wires is probably to touch the probes on the the connector pins through the holes in the side of the plastic moulding. Don't press too hard as these are the locking tabs that retain the pins in the moulding.)
Can you confirm that you ONLY got the voltage reading on the welding leads when the trigger was pressed.
When you said that you could get a spark from the torch tip was this a big spark that would melt the mig wire or just a tiny spark ?
Try this test. Remove the two black wires from JP1 and JP2. Tape up the ends so they can't short to anything. (Mark them so they go back the same way although it should not matter which way they go.) Connect your meter leads to JP1 and JP 2 set to a resistance range. It should indicate an open circuit. With the welder powered up press the trigger. The resistance reading should drop to very close to zero ohms. This is showing that the relays are operating correctly.
Check the fuse on the circuit board as this is the fuse for the motor.

Les.

sagor1 said:

There is a "remote" possibility the 24V transformer has a built in thermal fuse. I've had on fail on me before. They are on the primary, and taped inside the yellow tape that goes around the primary winding. Theory is, if the transformer overheats, it cuts out, permanently. However, those fuses also seem to fail with age. Options are to either replace the transformer, or carefully unwrap the primary tape to find that thermal fuse. No guarantee your transformer has one however. WHat are the ohm readings on that transformer, both primary and secondary. Any blown winding will be infinite resistance.

For your relays to click, there has to be some voltage feeding them, from somewhere. See if you can find the 24VDC source for the relays on the board itself. Trace that back to verify which transformer is supplying that 24V. I suspect the AC is being rectified on the board itself, so once you trace back from relay to the diode, it will be AC voltages backwards from there. It must connect via one of those connectors.

Click to expand...

Thanks, I will check if the transformer has a fuse.
Do you think I connected the correct colour wires to the transformer 240v primary.
Any idea why the black wire joins a red wire and shoots off behind the big transformer at the bottom of the picture.
See photo.

needhelpplease said:

Thank Les.
It is a Duel voltage 230v and 400v BUT the voltage know has a stop on it so you can't move it to 400v.
Defo no other relays on board. I put my ear as near as I dare and it was either one clicking or both, it's hard to tell.
But a defo click when trigger pressed.
If its ok, I will trace the wires and get back to you.
Thanks again Les, really appreciate your time and knowledge.

Click to expand...

Thanks,
the small PCB fuse was the first thing I checked. Its fine.


The spark was that big it would weld if the dam wire feeder worked.
I will try that with JP1 & JPR
thanks.

Did you measure the resistance of the 24 volt secondary winding ?

Les.

No Les, I am going to do that tomorrow.
Thanks for the heads up.

OK did a few checks.
Removed the 2 black wire from JP1 & JP2, taped up the ends, connected meter to JP2/JP1 and showed an open circuit with the welder on and trigger pressed.
I assume this is good ?


OK measured resistance on the transformer.


Primary
Set the meter to 200 ohms
Primary measured (0)
Set meter to 2k got a reading of .499


Secondary (blue wires)
Set meter to 20 ohms
Got a reading of 05.0


Then disconnected all that and connectedI the primary yellow wire to live 240v
Connected the red wire to neutral
Tapped off the black wire


Checked primary had 240v.
Reading on the secondary wires (blue wires)
Set the meter to 20v dc and got a reading of 0.18v
Set the meter to 200dc and got a reading of 0.2v


What's your thoughts please.

needhelpplease said:

Reading on the secondary wires (blue wires)
Set the meter to 20v dc and got a reading of 0.18v
Set the meter to 200dc and got a reading of 0.2v

Click to expand...

Well your problem seems to be right there...
When measuring the secondary voltage of a transformer, the meter should be set to AC volts, not DC volts.

JimB

Post#36
Ahhhhh, OK, let me check again.
Thanks

JimB said:

Well your problem seems to be right there...
When measuring the secondary voltage of a transformer, the meter should be set to AC volts, not DC volts.

JimB

Click to expand...

OK
Reconnected and got a reading of 35.8

I told you in post #24 what Jim has just pointed out that you had to set your meter to an AC voltage range to measure 24 volts AC. Re post #35 test between JP1 and JP2. It should have behaved as I said in post #30 but I think you must have done something wrong as when connected it was correctly switching the supply to the primary of the big transformer. Now I have convinced you that the small transformer is not faulty (Your voltage reading was higher than 24 volts as there was no load on the secondary and many small transformers have poor regulation.) we can start tracing the original problem of the wire feed motor not working. With everything connected back up, the welding current set to the lowest setting, the welder powered on and the trigger held on do the following. With the speed control first set to the minimum speed and then set to the maximum speed measure the voltages across the ends of the following resistors. and record them.R9, R4, R2 and R8. (8 readings.) Measure the voltage between pins 1 and 3 of connector CN3.
Short the ends of R8 together and note if the feed motor starts. Post the results.

Les.

Note that voltages around R8, R9 and maybe others may be DC voltages, not AC. However, there may also be a lot of AC ripple around those points.