Hello, guys,
recently I was using my S-998 desoldering gun and suddenly, BUM, electronics exploded inside the handle. Happily, no injuries.
I opened it up and found four components dead: two resistors (47k and 51k), a 22V zener, and a FR107 diode (all indicated in the schematic and the picture attached).
Some tracks have blown up also. I suspect, one of the devices failed and shorted. Replaced the affected components, used two jumpers instead of blown up tracks and voila, its working again.
Just for the sake of interest, I took my Cat S60 phone and looked at how it works through the thermal camera. Noticed that the resistor R5 is heating up like crazy, to almost 110 degrees Celsius.
For the sake of more reliability installed a 2W resistor instead of the original 1/4W. But I wonder, why is such resistance for current limiting is chosen? What bad could happen if I increase the value to, say, 100K? It would dissipate less heat, but I wonder would it create any problems?