Sharp R-430CD Microwave Repair (Completed)

[MWisBest]

My dad was going to fix this microwave years ago but never got around to it before his unexpected death this summer, so I decided to give it a shot myself for sentimental reasons. It is still a pretty nice microwave by today's standards though. 1100W, sensor cooking, etc. 

Initially I thought it was just going to be the blown thermal fuse. The inside of the chassis was completely clogged up with dust and debris, so wasn't exactly surprising that it got too hot inside. But then I discovered this:



Yeeeeahhhh. That transistor appears to be kinda cooked. It is part of the regulator circuit for all the microelectronic stuff on the control panel.
Unfortunately this is a proprietary transistor and package by Rohm (2SB1238) that is no longer made. It's designed to have more thermal dissipation than a standard TO-92. I did not have a TO-220 on hand that would work, so I came up with this:

That is a TO-92 MPSA56 with a wire crimp connector wrapped around it as a heatsink (plus some thermal grease in there). With the pins bent around because the pin-out was different. But other than that it was fairly close specification-wise to the 2SB1238, and more importantly I had it on hand in the salvage bin.

Here it is on the board:

I soldered the emitter to the extra unpopulated-but-connected hole there in order to increase the structural stability a bit, and give me more room for the swapped collector and base leads.

Just for good measure I replaced the electrolytic capacitors on the board as well, and created some solder bridges around that transistor to add some extra thermal mass:



Final result, works just dandy! It appears I may have broken a connection to the LCD, as one of the vertial lines is out, but it's still legible and more importantly the microwave works now. I'll take it.

[Armadillo]

  Well Done !