Repair an inverter welder

[edugimeno]

Re: Repair an inverter welder

Ok after a long time I put this welder back onto the workshop table
I still have the protecting diodes and the IGBT's removed (although I already have the new ones ready)
I measured the signal at the G leads of each IGBT's getting an oscillating signal of 0,5V at 66KHz. Then I tried at the E lead and there I gor about the same signal but with more noise and reduced amplitude to 0,5V. Im not sure as I wouild expect only the G gate to get the oscillating signal, and I have the actual transistors removed. Also the amplitude of the voltage getting to both IGBT's is different.

I see some small plug-in boards close to the IGBT's bethween the PWM boards and the IGBT's, soldered in vertical and with 3 or 4 SMD components, probably a Q and some R. Not sure if they need to be tested

I can't really invest much more time in this device, should I just go ahead and install the new IGBT's and Diodes and see what I get?

Thanks

[Crystaleyes]

Re: Repair an inverter welder

I can't see the vertical boards you mention...

Personally, I would suggest confirming that the IGBT's are receiving balanced signals from the SG3525 in order to avoid risking frying them, but as you seem determined to change the IGBT's, then just do it.
At the very least it will help clarify the situation.

[edugimeno]

Re: Repair an inverter welder

Ok....I will probably give up on this one:
(Note: I don't mind testing with the new Diodes/IGBT's before fully checking all the other componens as I bought a bag of 10 of each so if they burn in the first test, i can go deeper and still use another pair for the next attempt...)

So I went ahead today and tried it. Soldered the new IGBT's and diodes, checked all circuit for shorts/opens around all newly swapped parts, etc and powered it on. No voltage on output.

Checked the main large capacitor and they were 0v...So I started from the beginning..
Rectifier briseg with large heatsink: I got ~230V in input
Also I got 330v DC in its output, one lead from rectifier goes to capacitors. Other lead goes thu some components.... ut somehow they didn't get to the capacitors
I saw 3 or 4 smaller diodes around and checked them (with no voltage) in diode mode and they meausred OL on both directions....that's crazy! What happened now?

Is this still worth???

Thanks!

[petehall347]

Re: Repair an inverter welder

Ok....
I saw 3 or 4 smaller diodes around and checked them (with no voltage) in diode mode and they meausred OL on both directions....that's crazy! What happened now?



Thanks!

maybe they are tvs diodes and still good

[CapLeaker]

Re: Repair an inverter welder

There are bi-directional TVS diodes that would measure open either way. Post the part numbers.

[edugimeno]

Re: Repair an inverter welder

I marked the above mentioned diodes in the attached picure, and now that I see it zoomed, I realize that 2 of them are not diodes ae they don't even have the white stripe. Are they chokes?

But the other 2 at the bottom should read some 0.XXX voltage right?

Thanks

[petehall347]

Re: Repair an inverter welder

big ones tvs . other 2 look like regular diodes .

[edugimeno]

Re: Repair an inverter welder

There are bi-directional TVS diodes that would measure open either way. Post the part numbers.

Yes, they are probably...
One has a marking 1.5KE200CA which pdf states mentins the bidirectional option when no white stripe, for a dual 185V reverse diode
The other one seems to state CHN847 which doesn't seem to resolve into any diode I can find, but it's probably another dual D
They are around TNY255 which is an offline power switching driver.

Still lost....

[edugimeno]

Re: Repair an inverter welder

This schematic seems to share a lot with what I see in my welder...

https://danyk.cz/svar.png

[CapLeaker]

Re: Repair an inverter welder

I wood look that all the ICs like TNYxxx and UCxxxx getting power. The problem with both these PWMs is that they can fail and play dead or the lid blows off.
Take the IGBTs and the mosfet out and test them. Also test these diodes on the output of the welder. If power is there on these TNY and UC chips, I’d replace them and try again.

[edugimeno]

Re: Repair an inverter welder

Ok, update, LAST ONE, Short: It's going into the dumpster tomorrow
Long Story: I checked it again today. I wasn't getting the right voltages, there's a lot of rust or varnish or something on the solder joints so it takes a lot of force in the DMM pins to really sense the voltage. The large caps DO have 330V, so the IGBT's are "ready" tu pulse

I checked the TNY255 PS IC and it does put out 14V and the relay for soft start is working fine with this voltage

I also checked the transformer that gets the pulses from the PWM controller and has 2 output, one for each IGBT, and it gets 7v 44KHz pulses, and also power out the right voltage and Hz to the intermediate pulse adaptor circuits (the ones that drive the gates of the IGTB with a Q, some D's and some R's).
Then in the middle of this I was going to measure the voltage at the IGBT pins when one of the DMM pins slipped and caused a large spark, mains breakers triggered, and result of shorted IGBT's.... I have some spares but at this moment this repair is not worth to me, I informed my friend I would not invest more time into this thing so Im out...


Thanks everyone who helped with this repair, I learn a lot either with those that end up fixed, and also with those that end up discarded.

Sidenote to CAPLEAKER. If you see my first posts I had found the IGBT's and associated diodes shorted, and I had already swapped them by new ones. The 2 large output diodes tested fine. Thanks again.

[Crystaleyes]

Re: Repair an inverter welder

Seems a shame you're gonna scrap it. There is almost always some way to recover even the most random of electronic circuits.

Oh well...



I take it that you already tried hitting the polyphase discombobulator with a club hammer?

[CapLeaker]

Re: Repair an inverter welder

That sux…