Miller 375 Plasma Burt Cap..

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

I Need to remove the Plastic Cover So Removing & Checking The Transistors..

Waiting On Larger Nozzles for My Desoldring Gun.. Wish I had a Hakko Stocking dealer here.. Seems Like Motion Industries has Purchased all the cool stores and nixed all the good stuff!

Found another Open Capacitor did not go catastrophic but it is open..

All the IGBT's Seemed to Check Out With a Multi Meter.

[CapLeaker]

Re: Miller 375 Plasma Burt Cap..

I am thinking the problem started at the relay. Usually that is how it goes with these relays.

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

CapLeaker, I was messaged by a member on the miller forum that relay NT90RHAS24CB in the Hobart Variant Plasma and Welders is Obsolete and has been superseded by a Tyco Brand Because if it having issues / failing as well.

Looking at the data sheets..
TYCO T90S1D42-24

As Soon as I find my larger nozzles / solder wick or if kinco delivers my new ones which ever occurs first I will pull the 2X DSP 45-12A Diodes that are on the resistor circuit and check them.

Regardless, I am Going To Pull All the transistors to get a look under the plastic.

If All else fails = blog content right..

[CapLeaker]

Re: Miller 375 Plasma Burt Cap..

Reading esr on big hv caps is useless with a regular esr meter. You need to test the leakage at the rated voltage on these. I ran into that before a few month back on a Chinese plasma cutter. Finding a SM or schematic for plasma cutters is very hard. In my case I had to check every single stage, as there was no SM available. That burnt resistor I am guessing as being 100 Ohms as an inrush current limiter.I also think there may be other damaged invisible things.
The fet in the picture is a Fairchild KA1M0680B fet.
https://cdn.badcaps-static.com/pdfs/...e6bb8509e8.pdf

btw. Check and replace that relay too. If it failed, it will take out the inrush current limiter resistor.

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Miller is generally good for service manuals will call Monday. I do not see any other visibly damaged componants but there prob is something else that failed to cause the resistor to go nuclear..

[eccerr0r]

Re: Miller 375 Plasma Burt Cap..

Yeah, 100 ohm is very reasonable. That dot there is probably residue from the burn, I think KV-ohm would have used an E or R there if it were a fraction (but for that kind of power resistor, fractional dots make no sense as it would be better than 1%.)

I don't think 1000Ω or 100KΩ is a reasonable value there based on the location and its catastrophic failure, but can't discern the tracks on the board due to things going under components.

[R_J]

Re: Miller 375 Plasma Burt Cap..

The resistor brand is KV-OHM could be 100Ω

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Cleaned the Resistor

Only thing legible is

KV
100.



Other Side Totally Blown Out.

[R_J]

Re: Miller 375 Plasma Burt Cap..

The capacitor is a AVX FFB16J0395K
Try and clean the melted plastic from the resistor without removing the rest of the number, if you can

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Was A Midnight - 1am CL Deal.. I Will Dig a Bit Deeper Tonight.. Maybe Someone Here Has Experience In Repairing These.. Save It From the Trash Can.

The 472D makes Quick Work Of Removal Of Parts.

Bottom Of The Board

[eccerr0r]

Re: Miller 375 Plasma Burt Cap..

That melted gray device is a capacitor right? 3.9uF, (high) volts?

You probably can just check most of the IGBTs or whatever switching elements it's using, they usually do meltdown and short. The value of the resistor was probably fairly low but... darn these double sided boards...

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Resistor is Open.

Capacitor Reads 1,334uf ESR0.00 V Loss 0.6%

Grey Item Looks Like A Cap but Part Number Gives No Results.


Transistor Cannot Find Data Sheet.

[eccerr0r]

Re: Miller 375 Plasma Burt Cap..

That resistor may still have readable resistance? What does it measure?
What is that be that semiconductor on the black heatsink near the parts removed... that survived as well?
That gray item is a capacitor as well?

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Deleted Double Post.. But Searched all known sites including elektrotanya for SM to get part #'s..

[KG7AMV]

Re: Miller 375 Plasma Burt Cap..

Any One Got the Service Manual??

Taking out visiablly Burt parts..


Cap Is Ok other then Burns on Shrink Wrap. But will replace both with better if there is a recommendation..



Resistor and other parts Cooked.





Cannot tell part # Resistor.. Burnt.. Prob a bad IGBT>>> FFB3u93K ??

[KG7AMV]

Got a Miller 375 Plasma Burnt cap. Got for next to nothing craigslist.. No power..



1,500uf 250V (M) Panasonic? What would cause the cap to pop should I wire to a screw terminal style with D rings? Also Ceramic Resistor is Broken...



Anyone have a Service Manual I stripped to the board ish.. 1 tab was broken that holds heat sink.. center bottom.. Nit top unless i break out desoldering gun..



Bottom


Big Simple Mess..