inverter welder not working

[aidank]

I have a kuhtreiber kitten 170 https://en.kuhtreiber.com/products/invertory-mma/kitin-170/ Bloody good inverter. It doesnt do a lot of work, its stored in shed on a shelf.

Was using it wet day last Feb and when I plugged in and turned on, 2 seconds later there was a loud bang and tripped the trip switch. no smoke. I thought it was dampness somewhere, Turned back up the trip switch and all was good, burned my 5 6013 rods at 90amps.

Welder was idle for a month sitting on the shelf and when I used it middle of March there was a repeat of the above incident, a loud bang and tripped the fuse. no smoke Turned up the trip switch and did the bit I had to do no issues, and left the welder on the shelf.

Last Saturday I had another bit to do and when I pressed the switch to turn it on, the lights on the welder flashed on and then cut out. After the 5th attempt the welder started up. I thought I had a faulty switch.

First spark of the rod the welder cut out and now it just flashes the light when I try to turn it on and thats all it does. Its not tripping the fuse.


Any ideas

 

[zzr1200]

Take the covers off check for loose connections and post some photo's of the inside bits, we maybe able to spot something...

 

[aidank]

Take the covers off check for loose connections and post some photo's of the inside bits, we maybe able to spot something...

Tried again this evening and it started on the second press of the switch.

Burnt 1.5rod without issue so switched off and on again no issue.

Tried to resume welding and first touch of the rod and the whole lot cut out.

Removed covers no burning or any issues anywhere. Capacitors look perfect anyway.

Tried to start again with cover off and it started as expected.

Tried to weld again and as soon as I touched the rod to metal, there was a sizzle for about 1 seconds, fan slowed down a bit, still no burning smell or issues. No wires that I could find getting hot.

After the sizzle stopped tried to weld again and away it went perfectly. Tried another rod at full power no issues.

Tried a further 20 times and worked perfectly.

Reseated the wires going into small round transformer just in case there was a bad contact doesn't appear to be. Picture 5.

Few pics attached. Contacts in Relay in picture 4 looks fine

 

[eddie49]

The fact that the welder starts working again after failing indicates that the fault is a contact problem rather than a broken component.
Start by disconnecting the machine from the mains and waiting an hour or two for the capacitors ( with up to 325v DC ) to safely discharge. Then remove the covers and check for:
- loose push-on spade tags at the back of the mains power switch and on the bridge rectifier ( rectangular alloy block mounted on a heatsink, with 4 tags ). The connectors carry high current and often are poorly seated or work loose. If in doubt, they can be soldered permanently.
- loose bolted connections on heavy internal cables and copper or aluminium busbars, at heatsinks, and on thick tracks on the PCBs, and at the back of the front panel sockets.
- loose or poorly-seated plugs on the multi-wire harnesses between the PCBs
- any sign of blackened, burnt, or split components, especially the multiple paralleled power semiconductors ( MOSFETs, IGBTs, and diodes ) that will be attached to the large finned heatsinks.

If you are confident working on live equipment, measure the DC output from the bridge rectifier(s). It should be about 325v DC, after smoothing by the large electrolytic capacitors. It is this DC bus that runs the machine.
There is usually a soft-start circuit, using a resistor or thermistor bypassed by a timed relay, to lessen the initial power-on current surge as the capacitors charge. Check if you can hear this relay click just after switching on the machine.

 

[aidank]

The fact that the welder starts working again after failing indicates that the fault is a contact problem rather than a broken component.
Start by disconnecting the machine from the mains and waiting an hour or two for the capacitors ( with up to 325v DC ) to safely discharge. Then remove the covers and check for:
- loose push-on spade tags at the back of the mains power switch and on the bridge rectifier ( rectangular alloy block mounted on a heatsink, with 4 tags ). The connectors carry high current and often are poorly seated or work loose. If in doubt, they can be soldered permanently.
- loose bolted connections on heavy internal cables and copper or aluminium busbars, at heatsinks, and on thick tracks on the PCBs, and at the back of the front panel sockets.
- loose or poorly-seated plugs on the multi-wire harnesses between the PCBs
- any sign of blackened, burnt, or split components, especially the multiple paralleled power semiconductors ( MOSFETs, IGBTs, and diodes ) that will be attached to the large finned heatsinks.

If you are confident working on live equipment, measure the DC output from the bridge rectifier(s). It should be about 325v DC, after smoothing by the large electrolytic capacitors. It is this DC bus that runs the machine.
There is usually a soft-start circuit, using a resistor or thermistor bypassed by a timed relay, to lessen the initial power-on current surge as the capacitors charge. Check if you can hear this relay click just after switching on the machine.

cant find anything loose

no sign of blackened or burnt componends.

will have to do a bit of googling on that bridge rectifier, is it shown in any of my photos

Pic 4 above shows a relay, is that what you are referring to in your comment above.

Its this model https://www.reichelt.com/ie/en/shop...term=4576236144095869&utm_content=Ad group #1

Contacts look good in it, it clicks within 0.5seconds of startup and can see the contacts engaging.

 

[eddie49]

On some inverter welders the input bridge rectifier is bolted to the case, or on top of a heatsink, and then connected with four wires and spade tags. On yours, it is soldered directly into the PCB, and the small square heatsink is placed on top of it.
If you follow your link in Post #1 and select the User Manual, then go to Page 54, the rectifier is Item 23, P.N. 41899.

It would still be worth checking the integrity of the rectifier joints at those 4 tags on the PCB side.. This also applies to all the solder joints on the PCB, especially thick wires or pins on high-current or heavy components - such as the ferrite-core transformers and the power transistor/heatsink assemblies. They are sometimes fastened or glued to the board, but with shock or vibration their weight can break them loose, fracturing the connections.
If you are sure of all the PCB joints, then maybe a local phone repair shop could check that for you. One of my local places has a stereo microscope and hot-air solder rework station.

The relay is near to the varistor, item 8 in the first picture on Page 54 of the User Manual. This component is bypassed after the initial soft start period, so that relay probably is indeed the soft-start one. Its operation proves that the control logic and control power source are working correctly.