I've detected a possible cause of my problem. I disconnected the power, tied the trigger closed and did a continuity check on the wires from the PCB where they showed. I got a reading on one of the 24v out wires but not the other and looked closely at the back of the pcb just to trace where it went and there was a very small damaged section of copper trace. Now I need to figure out what to do about it.....
- Thread starter Davidmadd
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Hi Eddie, those two both read TIC 126D underneath Malaysia, then 401....
hotponyshoes
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Were does either end of that track end up?
Something that would be easy to solder a cable bridge onto?
The normal way to fix a burnt or broken PCB track is to clean both ends of the break - scraping the lacquer off - then solder a short piece of solid copper wire across the fault. However, we need to be sure that it is really a break, rather than just two adjacent tracks. Are the ends of the track sooty, scorched, burnt or lifted from the board? A photo would help to decide if this is a real problem.
The fact that the clear-cased relay operates and the wirefeed works ( presumably, on demand when pressing the trigger, and variable by the speed pot? ) means that the torch trigger signals are getting to the board, and also that the aux power transformer is supplying the board.
The two 3-lead components - TIC126D - are silicon controlled rectifiers - SCRs, or thyristors, not Triacs. They are effectively controlled diodes, and can not run an AC load. The two SCRs, together with the adjacent two large diodes, form a controlled bridge rectifier, which will be used to provide speed control for the wirefeed motor. Therefore, if they do not drive the AC contactor and the gas valve, it must be the relay that does it. Are the contacts on the relay clean?
The fact that the clear-cased relay operates and the wirefeed works ( presumably, on demand when pressing the trigger, and variable by the speed pot? ) means that the torch trigger signals are getting to the board, and also that the aux power transformer is supplying the board.
The two 3-lead components - TIC126D - are silicon controlled rectifiers - SCRs, or thyristors, not Triacs. They are effectively controlled diodes, and can not run an AC load. The two SCRs, together with the adjacent two large diodes, form a controlled bridge rectifier, which will be used to provide speed control for the wirefeed motor. Therefore, if they do not drive the AC contactor and the gas valve, it must be the relay that does it. Are the contacts on the relay clean?
I've attached a photo so hopefully it you will see that. I'm pretty sure its a break as there is a short piece curled back which doesnt show in the photo. I have looked ay a you tube clip of someone doing a solder repair but its close to other tracks and I have seen a Dry Film repair method so may investigate that option
Yes, that is definitely an overheated and burnt track. I think all the tracks were covered with solder during the flow-soldering process, and the lacquer burned off when this track overheated. I would suggest the repair should be made with a jumper of thin insulated flexible wire, from the right-hand solder pad across to wherever the next solder pad is on the track off to the left, laid close to the board and maybe fixed with a spot or two of hot glue.
However, before doing that we need to know what part of the circuit this track represents and why it burnt. Otherwise, it would be like replacing a blown 5-Amp fuse with a 10 Amp one and hoping for the best. It is not easy to reverse-engineer a circuit diagram, but we can make a guess if you could post photos of both sides of the board.
However, before doing that we need to know what part of the circuit this track represents and why it burnt. Otherwise, it would be like replacing a blown 5-Amp fuse with a 10 Amp one and hoping for the best. It is not easy to reverse-engineer a circuit diagram, but we can make a guess if you could post photos of both sides of the board.
I actually found it by the following:- I tied the trigger closed, in my mind closing the circuit. I then thought I should see some continuity through the wires. I got a reading between the two 27v supply wires and one of the coil activating wires but not the second coil wire. I turned it over and followed the trace back from that wire and soon found the damage on the trace that supplies the wire in question. Of course there was no power to close the small see through relay, so it was coincidence only that led me to the break.....here's a couple of photos.....
Solder a wire from that pin down to the first pin you come too, to be honest that second pin from the left - that track don’t look good either .
David, thank you for your quick reply and those two excellent photographs.
Holding the PCB with the components facing you, the green 8-pin connector is on the left. Referencing the circuit diagram of the whole machine in my post #5, the connections, from Pin 1 on the left:
1 - to the Contactor
2 - to the wirefeed motor
3 - the trigger switch
4 - ditto
5 - 27v AC in
6 - 27v AC in <--- Damaged
7 - to the Contactor <--- slight damage
8 - to the motor
Now looking at the back of the board, the burnt track is Pin 6 -- 27v AC in. The next track, Pin 7 - output to the Contactor, does not look too good either, where it goes down towards the centre of the board - the lacquer looks burnt.
Pin 6 has a heavy track going down to a very large diode ( black tubular component ). This is one of two that, together with the two SCRs I mentioned in post #26, form the controlled bridge rectifier to regulate the wire speed. The track also goes to a group of 4 smaller diodes, which are the bridge rectifier to get a DC supply to run the rest of the logic on this PCB.
The burnt thin track which rises from Pin 6 goes across the back of the board, towards the left, and then down towards the relay. It joins to the centre pin of a 3-legged component with a metal tab, which is adjacent to the relay case. The rather scorched track from Pin 7 also goes to that component. Could you please read the part number of that component? I guess it is a Triac, and it has failed! ( Hoping the number is visible and not facing the relay case.)
Holding the PCB with the components facing you, the green 8-pin connector is on the left. Referencing the circuit diagram of the whole machine in my post #5, the connections, from Pin 1 on the left:
1 - to the Contactor
2 - to the wirefeed motor
3 - the trigger switch
4 - ditto
5 - 27v AC in
6 - 27v AC in <--- Damaged
7 - to the Contactor <--- slight damage
8 - to the motor
Now looking at the back of the board, the burnt track is Pin 6 -- 27v AC in. The next track, Pin 7 - output to the Contactor, does not look too good either, where it goes down towards the centre of the board - the lacquer looks burnt.
Pin 6 has a heavy track going down to a very large diode ( black tubular component ). This is one of two that, together with the two SCRs I mentioned in post #26, form the controlled bridge rectifier to regulate the wire speed. The track also goes to a group of 4 smaller diodes, which are the bridge rectifier to get a DC supply to run the rest of the logic on this PCB.
The burnt thin track which rises from Pin 6 goes across the back of the board, towards the left, and then down towards the relay. It joins to the centre pin of a 3-legged component with a metal tab, which is adjacent to the relay case. The rather scorched track from Pin 7 also goes to that component. Could you please read the part number of that component? I guess it is a Triac, and it has failed! ( Hoping the number is visible and not facing the relay case.)
Hi Eddie - OK - I've figured out the component you mention unfortunately being tight against the relay, I cannot see any markings etc. The face of the metal piece has no markings. Is there a way I can test the component whilst its in place???? I can access the three contacts underneath. If you suspect that this has failed I could remove it and then could see the markings and maybe test it remote from the PCB if I knew how!!! I have had a look on you tube how to test a triac but that was on an item on the desk and not buried in a PCB....
My knowledge of electronics is very limited. I've used a test meter set to "Continuity" and there is nothing showing between each of the contacts but I dont know if that is significant? If I use the Ohms function I can get a reading between 2 contacts only on the K Ohm scale???
Would with the tracks looking like they are lifting away cause it to burn out at all ?? Just I’ve never seen a board in that condition before
Sorry for the delay in replying. I have been to my lock-up garage to check the resistance of a contactor with a 24v AC coil - it is 6.9 Ohms. A datasheet on this site:
www.quora.com
states that a 24v AC coil should have a resistance of 6.19 Ohms. Your new contactor is 8.5 Ohms, so all these values are close. However, the original contactor was only 3.9 Ohms, a lot lower. I don't know how that happened, but it seems that it is partially shorted, and would have been drawing a lot of current, leading to the tracks overheating and lifting and burning through.
The Triac ( assuming that is what it is, and it really must be ) is mounted "face down", so seen from underneath the left-most pin is the Gate - actually Pin 3 in a normal view. The other 2 pins, centre and right, are actually Pins 2 and 1, and they are 27v AC in ( from Pin 6 of the green connector ) and AC output to the contactor ( Pin 7 of the connector ).
On a Triac the two AC pins ( centre and right in our upside-down view ) will conduct in both directions, but only when the Gate ( left pin ) is triggered with about 3 volts. I now think the Triac is probably OK, it was conducting when required, but the coil resistance was too low, which burned the tracks.
You could carefully solder a short thin solid bare copper wire across the burnt track, ensuring that it does not touch the adjacent tracks, or as Hutcho suggested, solder an insulated jumper wire from the connector pin down to the Triac centre pin.
After that, install your new contactor and re-assemble the machine. I'm fairly confident it will work !
[ If I'm wrong and the Triac is shorted, the worst that will happen is the contactor will be on all the time.]
What is the resistance of a standard 24 V coil?
Answer (1 of 3): I( don’t think there is such a thing as a “standard” 24V coil. Particularly when there is no standards organization name behind it. They come in all sizes. Perhaps for that manufacturer there is a standard coil but the applications worldwide are very diverse depending on size an...
The Triac ( assuming that is what it is, and it really must be ) is mounted "face down", so seen from underneath the left-most pin is the Gate - actually Pin 3 in a normal view. The other 2 pins, centre and right, are actually Pins 2 and 1, and they are 27v AC in ( from Pin 6 of the green connector ) and AC output to the contactor ( Pin 7 of the connector ).
On a Triac the two AC pins ( centre and right in our upside-down view ) will conduct in both directions, but only when the Gate ( left pin ) is triggered with about 3 volts. I now think the Triac is probably OK, it was conducting when required, but the coil resistance was too low, which burned the tracks.
You could carefully solder a short thin solid bare copper wire across the burnt track, ensuring that it does not touch the adjacent tracks, or as Hutcho suggested, solder an insulated jumper wire from the connector pin down to the Triac centre pin.
After that, install your new contactor and re-assemble the machine. I'm fairly confident it will work !
[ If I'm wrong and the Triac is shorted, the worst that will happen is the contactor will be on all the time.]
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Wow, thats really great, many many thanks.
I think I will repair the track by using a piece of insulated wire between the pads as there is maximum room there for the soldering iron. I would also ask advice about connections on the contactor. I know, because I took photos, that one white wire (from the PCB, 24v) goes to A1, the other goes to A2. Live power supply goes to Term 14. a black wire from PCB to 6, Blue, neutral to 4. Black from PCB to 2. - Cant recal just at the moment where the two black wires come from, probably actual ON switch?
Large heavy duty white wire from 1 to rotary power selection switch. ditto from 3. The power supply for the gas valve comes from A1 and A2. Metal tags link 2 to 4; 6 to 14 and 1 to 3 and 5 to 13.
Although I took photos, the colour is not overly clear due to loads of dust on the cables. I dont want to ruin all the hard work and efforts from all who responded by making a silly connection error.
Many thanks again
I think I will repair the track by using a piece of insulated wire between the pads as there is maximum room there for the soldering iron. I would also ask advice about connections on the contactor. I know, because I took photos, that one white wire (from the PCB, 24v) goes to A1, the other goes to A2. Live power supply goes to Term 14. a black wire from PCB to 6, Blue, neutral to 4. Black from PCB to 2. - Cant recal just at the moment where the two black wires come from, probably actual ON switch?
Large heavy duty white wire from 1 to rotary power selection switch. ditto from 3. The power supply for the gas valve comes from A1 and A2. Metal tags link 2 to 4; 6 to 14 and 1 to 3 and 5 to 13.
Although I took photos, the colour is not overly clear due to loads of dust on the cables. I dont want to ruin all the hard work and efforts from all who responded by making a silly connection error.
Many thanks again
I suppose everyone has their own method for identifying wires. I always start by making a hand-drawn diagram. If the wires are the same colour, I use a permanent black marker to draw multiple rings around each wire, to identify them as 1,2,3 etc., but this only works for half a dozen or so. Tie-on labels are OK; I don't trust paper or tape labels, they dry and fall off - especially if your projects wait decades to be completed!
I agree that the 24v AC operating coil is terminals A1 and A2, with wires from the PCB, and parallel wires going to the gas valve from the same two terminals.
It is a 3-phase Contactor, with the three main contact sets being L1, L2, L3 in, and T1, T2, T3 out. These are also labelled 1,3,5 in, 2,4,6 out. The "in" and "out" feeds can be reversed. There is also another set of "auxiliary" contacts, labelled 13 and 14. These contacts are operated by the moving armature in the same way as the main set.
Effectively, there are four on/off switches here. The metal links 2 to 4 and 6 to 14 mean that two sets of contacts have been paralleled to share the current for Neutral ( 2 and 4 ) and Live ( 6 and 14 ).
There are corresponding metal links on the "output" side, joining 1 to 3 in parallel for Neutral and 5 to 13 for Live.
As you thought, the black wires from 6 ( Live ) and 2 ( Neutral ) go the main On/Off switch, and then on to the 240/27v AC auxiliary transformer. That transformer gets AC power as soon as the machine is on, before the contactor is pulled in in response to the torch trigger switch.
The only concern I have is with the two heavy white wires that go to the main welding transformer via the rotary power selector switch. The wire on 1 will be the Neutral feed to the transformer, but the other wire cannot be on 3, because that is also Neutral ( there is a metal link from 1 to 3 ). I think the second heavy white wire must go to 5, for Live.
I agree that the 24v AC operating coil is terminals A1 and A2, with wires from the PCB, and parallel wires going to the gas valve from the same two terminals.
It is a 3-phase Contactor, with the three main contact sets being L1, L2, L3 in, and T1, T2, T3 out. These are also labelled 1,3,5 in, 2,4,6 out. The "in" and "out" feeds can be reversed. There is also another set of "auxiliary" contacts, labelled 13 and 14. These contacts are operated by the moving armature in the same way as the main set.
Effectively, there are four on/off switches here. The metal links 2 to 4 and 6 to 14 mean that two sets of contacts have been paralleled to share the current for Neutral ( 2 and 4 ) and Live ( 6 and 14 ).
There are corresponding metal links on the "output" side, joining 1 to 3 in parallel for Neutral and 5 to 13 for Live.
As you thought, the black wires from 6 ( Live ) and 2 ( Neutral ) go the main On/Off switch, and then on to the 240/27v AC auxiliary transformer. That transformer gets AC power as soon as the machine is on, before the contactor is pulled in in response to the torch trigger switch.
The only concern I have is with the two heavy white wires that go to the main welding transformer via the rotary power selector switch. The wire on 1 will be the Neutral feed to the transformer, but the other wire cannot be on 3, because that is also Neutral ( there is a metal link from 1 to 3 ). I think the second heavy white wire must go to 5, for Live.
OK, Thanks very much. That has clarified the two heavy duty wires. I labelled the wires using tie wraps that have a little labelling platform on them but they are not easy to write on being white plastic. On the wire from no 5 I smudged the ink and it looked like a three. My photos as to where it went were inconclusive. Earlier I did put it back into "3" and when I manually closed the magnetic switch to check if I was getting an arc it blew the fuse in the plug so I knew something was back in the wrong place. Now I will get on with the PCB repair and refit the contactor. I will be sure to update you on results early next week.
Once again many thanks to all who responded and helped me move forward.....
Once again many thanks to all who responded and helped me move forward.....
