Hi atax, welcome to the forum.
Well that's an impressive way to remove the legs from a mosfet packeage! I'm glad you are chastened rather than injured.
I've been pondering the sequence of events...
- I suspect that you were working with the tip not grounded, but your power supply is a decent one with grounded output.
- When the tip touched the phase connection, the insulation on the element broke down, at the positive end because the fault current has clearly passed down the +ve line through the mosfets.
- From there, it probably found a path through the +ve line of the power supply to ground, either that or it found a path through Gate-Source breakdown of the mosfets and through the TS100 circuitry to the grounded PSU -ve.
As you say, the tip will have been destroyed, and obviously the mosfet package. What concerns me is what other damage has occured. The main worry is that the buck regulator U2, which feeds the logic supply from the main +ve rail may have broken down internally, passing some portion of mains to the microcontroller, display etc. There are also non mains rated capacitors and transistors in the mosfet gate feed and regulator input that might have gone short. There is a 24V protection Zener (D3) which might have clamped the surge, but probably have taken out D4 and R30 in the process.
I suggest that you proceed as follows..
- Check that there isn't a short circuit reading at D3 and then try to power the TS100 from a 5V supply via the microUSB connector. If the display doesn't show something then U2 and/or the logic probably died. Check for 3.9V output at U2 and 3.3V at the output of U5.
- If you get past that step, check the functionality of your power supply - does it still put out the expected voltage?
- If both of the above succeed, then carefully check all the passives, (and Q2) between Vin and U2 and also the Po signal path from CN2.
The mising pads on the mosfet footprint won't be a problem if you go for the parallel mosfet configuration in the OP, but I'm afraid you have rather a lot to check first. Of course, you will need to replace the tip before trying a heating test.
Yes, Good luck.
Hey, thanks for the quick reaction!
As usual, i wasnt patient, but found some 4925 at local store(small wonder in itself).... let me explain
Here are some things I didnt tell before:
After the whole incident(iron wasnt grounded, the point of it occured to me after), I flipped breakers on, got back to my "workhole", small place I set my tools up in our flat.
Checked the area, checked the lamp, on to the TS100...it turned on, didnt recognize the tip, thats when I found out.
a miracle in itself
So ok, its on, fried tip, no biggie, lets swap it for another...oh ok, wont heat above 24C...so somethings off.
I picked it apart, immediately seen pieces fall out and carbon residue all around, started cleaning and saw the mosfet(had no idea initially what the IC is) blew up...
Google got me to your post, so glad it did and the course of action was clear.
Knowing our local options here from experience, I got on aliexpress and ordered replacement mosfets, both kinds and 2 oleds as well, since I burned it a bit during IC removal(turns out to be ok, just the upper layer got heat)
Kicking myself about what happened I went out to 1/2 of our local parts shops trying my luck...and lucky I got, 4 Si4925 in stock, got two, just in case.
Off of that bit of good karma I got home, did some work, started lunch...taped the PCB, did prep work.
Managed to find my Lidl, Parkside 3AA battery 4.5W soldering iron I modded to be able to run it off my LAB PSU...
Did the mosfet replacement, knowing the iron worked after the incident, did the mod like in OP last pic.
Et Voila! It works!
What a ride... have to do some real work with it yet, but Im confident its alive again. Hopefully it will stay that way, at least until I have another
moment
Got the whole set from Novel Life (or really close) store from Aliexpress, silicone psu cable and so on, so its not like the generic chinesium stuff I guess.
Cheers