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Industrial PCB Repair Without Schematics - Practical Example - MIG Welder
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- Опубликовано: 15 май 2024
- Repairing PCBs from industrial and similar equipment requires a different approach to fault finding, but master it and this can be very rewarding and profitable work. Here is an example of how to approach this type of repair.
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Thank you
Richard
*The welder PCB is now repaired - part 2 coming tomorrow, let's see what actually caused the fault*
I'm a welder, running my own fabrication shop at present. I'm learning electronics so I can come out of a dirty workshop and change my career to electronics. This repair video is right up my street lol.
part two coming today
Richard thanks for sharing. I’m in the process of troubleshooting a small circuit board . This video has showed me many good ways to do it. Really Richard I follow all of your videos but this one really opened my eyes. Thank you. 👍. Artie
Well it’s 4am now. Just finished watching your vid. It reads like a whodunnit mystery novel. Will the killer be revealed in tomorrow’s episode Rich😮?.
Nice work Richard, thanks
Pin 4 of the LM324 connects to other components too, not just the hot resistor. We could see this when you turned the board over. It probably has a decoupling capacitor (leaky?), or perhaps one of the other components that the resistor supplies is the problem. I wouldn't change the LM324 yet, until youv'e checked out the other components that connect to the hot resistor.
You will find out in part two -tomorrow 🙂
My guess is there is a Zener diode hidden under the 0.15 ohm resistor..... and it's shorted. If so, that's effecting the voltage measured at the LM324 and causing the 1/2 watt resistor to be exposed to the full voltage instead of the full voltage minus the zener voltage. I can't wait for tomorrow's video!
What makes you think that?
I notice the relay is only 24 Volts, is the input too high (power)? Does the relay work?
MIG welders if you are not using a fluxed wire uses a gas to shield the weld.
Basically you have gun where the wire is fed out, where this wire is fed out there is a shroud that supplies an inert gas around the welding area. The gun has a trigger, this is just a micro-switch in the handle.
The controller will control both the gas and wire.
The wire is fed by a DC motor, the speed set by the controller. (one of the pots)
The Relay may be the gas, not sure, it could activate the welding current. Gas has a delay when releasing the trigger on the gun.
Depending if this controls everything on the welder or just the feeder unit.
It was a long time ago when I used a MIG welders, The ones I used where big ones with a separate feeder to the Current Transformer.
If this is a small modern one, and its Current is handled with solid-state components then I could be totally wrong.
If it is just the feeder unit. The gas should continue for a little while wile the weld cools when you stop welding. The time adjusted by the other pot and the welding current is controlled by switches on the main unit.
If this controls every thing including the welding current then the other pot is for the current control and maybe the relay turns off the current (probably still the Gas). the little pot on the PCB probably controls the gas delay.
If the welder does not use gas and only fluxed wire, ignore every thing I have said 😁 haha.
Its a shame he did not give you pictures of the welding machine. or even the name of it?
Hope that helps and not confuse things.
Great fault finding video. I agree with you and Manticore1960 that the short is after the resistor 820 ohm. But which other components are behind this resistor else than the Opamp, connected to ground? The tantalum capacitors are notorious of going short.
I will be watching the conclusion. Best regards Henk
I guess you just have to wait until tomorrow 😉
Very interesting. 36.3V across a 35V electrolytic, I do hope not (in my opinion). Perhaps those nasty-looking power resistors are dropping a bit. Resistive dropper to power an opamp, no expense spared for a stable supply.
When the board was turned over, we could see that the big capacitor was connected directly to the + & - of the bridge rectifier. With 27.4vac coming in, that does correspond to over 35v on that capacitor!
@@Manticore1960 Indeed, wishful / hopeful thinking on my part that it was meant to show 24.7V AC (27.4V, I can't believe). Even so, a bang waiting to happen (in my opinion). There's also something very strange with a circuit that uses a dropper resistor to power an opamp, fed from a rail that is probably glitching all over the shop.
@@ralphj4012 Even 24.7vac when rectified & smoothed, is still very near the working voltage of the cap. Somethings not right here.
Agree about the dropper resistor, but there are other components on that line, including the cathode end of 2 diodes. Are these perhaps zeners that have gone faulty? Although Richard did check the forward drops with his meter.
@@Manticore1960 Agree, in my day it was good practice (in my opinion) to select capacitors with at least 20% more volage handling capability than what you expect.
To be fair those voltage readings were provided to me, I didn't measure them myself, maybe Rodger will post here
Great video. You mentioned that unused op amps within the Quad device might be grounded. I tried that once and it gave bad results (large current draw). TI actually have a tech note ‘how to properly configure unused operational amplifiers’. I found it helpful.
Didnt have a clue rich but the luck your having just lately with chips lol i wouldn't be surprised 😁👍
I would have removed the op amp and remeasure the current to make sure no surrounding components like capacitors are shorted to ground before condemning the op amp. remember the Capacitor that was changed?, the old one probably sent high ripple or a voltage spike to the op amp causing possibly additional problems like the other IC . More checks are required before changing the LM 324.
Nice suggestions - all will be revealed (well not all, but you get the gist) in part 2 tomorrow 😉
Yes ! Yes ! Yes ! Just for once I actually know something about something that Richard doesn't, as I have welders and do welding 😂
But thats it ! Im then lost 😆Over to you Richard.
Then you had to pick up that Toolup ET13S that I've been trying to tell myself I don't need 😍🥰
But its sooooo useful and most importantly has diode bleep ❤
I feel a weakness in the force 😅
That is not the entire welder supply. MIG torches need about 30-70 VDC at 50-150 A, which obviously is not handled on this board. The power components on the PCB most probably deal with the wire feed motor speed and maybe the pulse feed to the external SCR or IGBT which feed the arc.
This is the only part of it that I have, and I know nothing about MIG welders, just how to diagnose PCB faults (some of the time)
Commodore VIC-20 uses the same bridge rectifier.
👍
Heya, not much else left on the board no tested so yeah it could be the chip
No, welders run on low voltage, high current.
I think there's a switch- I've used a welder- not 100%, but I think that if your wires not coming out, there will be no power to your tip. (Large current, low voltage.) -It's the current that melts the steel. The Flow of electrons is required!
I am guessing the faulty capacitor effectively not in circuit caused ripple and destroyed the op-amp?
i would check the blue tants as i am coming across a lot of leaky ones .
Wouldn't they have been red hot?
Hi Richard 🤗
45:42😳😳 pay attention with your super long unisolated measuring tips. You are making a short circuit.
That 820 resistor looks to be a half watt resistor. 22 V cross it would be more than a half watt. Seems like it’s worth the cost of the chip to replace it and see what happens. Maybe remove and recheck. I’m a little concerned that the voltage rating of the big cap is a smidge low. The rectified DC should be more like 37v
I am only up to the inspection part of the video and I see some bad solder joints on that op-amp chip...
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I worry a little about the trimmers not going back to their original settings. You could redo them.
I thought that too, but then noticed they have spindles that are presumably available on the front panel, so can be adjusted when back in it's box, presumably they are labelled.
Are you talking about the big ones that go through the board ?
They are used to adjust the welding wire speed and possibly a timer for regular spot type welds so the user would adjust them a lot and reset them for different welds so not a problem.
The other ones ... I've no idea 😅😅
At 22:20, What does he mean when he says the gate is floating? And how does the resistor factor into it?
He means it is not being ‘pullled up’ to a high voltage or ‘pulled down’ to a low voltage so that it normally sits it one state (on or off) until it is actively driven. That’s how a gate is often managed, so you have good control of the output. If it ‘floats’ it can sit in either state (on or off), which suggests whatever was supposed to be driving the gate is no longer doing that very well
duty cycle
LM324 is prone to burn...i would change it.
MIG welder voltages are around 12-15V but high current. (The wire feed is not insulated so would you want several kV as you suggested hanging around.... LOL)
The pot at 25 minutes wasn't put back to where it started. It was a 3 o''clock , you put it back to about 2 o'clock.
Was enjoying this, as always with your videos but gave up just over half way through after a 4th set of 1 minute adverts. 😢
I;m sorry the adverts were a problewm for you. They are palced by RUclips, the video creator has very little control over this now since the latest policy updates. Also different viewers will see a different quantity of adverts in the same video
I was tired of all the ads on my utube vids, I use mozilla to access the internet and use their ad blocker extensions, they work really well, not 1 single ad in the whole video.