Sharp Twin Famicom Repair Log 3

[chimyfolkbutter]

Ok, I spent a day trying to figure out why the Twin would continually receive a media set signal.  What this means is that the Twin thinks that there is a disk in the system and it tries to read the disk.  Unfotunately, their is NO disk in the system.  It just keeps rebooting so to speak.

So, as I started to reverse engineer the connections etc.  During my session, as I was testing Transistors, I accidently shorted the transistor.  Q203 (B941 PNP) to be exact.  My probe touched both the base and the emitter at the same time.  Not good.  The result?  Video is all gone.  The Famicom PPU is running hot (hot when you touch it) and the transistor that drives the Voltage regulator is running real hot.

So I spent the day reverse engineering the video circuit and the power board.  I figured that out and identified all the transistors and other discrete electronics.  Some of the transistors are not readily available so I had to find equivalents.   I am documenting this so I will write it up for the famicom workshop.

Now, I was able to test the Q203 transistor that I shorted and the video transistor Q202.  I performed some manual tests across the PNP and NPN junctions of the transistors.  Low and behold, the PN junctions are conducting when I revese the polarity of the test leads.  Q203 is conducting over the Base Emitter Junction when the leads are reversed.  It is also conducting over the Collector Emitter.

Q202, the PN junction is conducting over the Base Emitter when the test leads are reversed.

In English, I blew the tranisitors out!

So what is next?  I gotta order some transistors, desolder the defective ones and resolder the new transistors.  Then I will be back to square one.

I knew this wasn't going to easy but dang, I shouldn't have shorted the transistor! 

Stay tuned...

[kite200]

that sounds like a hard repair. What color is this said twin famicom?

[DevIancE]

I wish I knew how to do all of that stuff.   ...Then maybe I could fix my Famicom.

[Nickv]

ive got a regular famicom that doenst work. Im gonna get my brother who's better at electronics then me to take a look.