...but I make up for it with loads of stubbornness!
I've got a small homegrown music box which sports a 20x4 LCD and an infrared receiver for interaction. When I set it up with lcdproc, I realized that their wiring diagram for controlling the backlight asks for a pnp transistor (as it uses the nSel parallel port line which is active low). I didn't and still don't have any of those, so I simply soldered in an npn with the result of the backlight logic being inverted.
Of course such matters can be resolved in software. But on taking a peek at the code in question, I decided that I don't want to get my brain dirty fingering this messy stuff.
So, how do you cleanly invert a TTL signal using only npn transistors? I had no idea, as my practical electronics-fu is piss-weak, too. The play-hookey site as well as allaboutcircuits were very helpful, while this lcdmodule schematic simply didn't work as I found out after some laborious messy experiments with tons of test leads. I won't bore you to death with the details, but in the end I actually managed to understand how an RTL inverter works and how I can switch the actual current-controlling transistor with it. Soldered in 1kohm and 10kohm resistors, minimizing space usage as you can see from the photos below (but maximising the mess) and it works.
SC1959 transistors are tough beasts! I had salvaged two of them from something else, and managed to fry one pretty badly: sent over 1A through it and apparently not across the junctions where it should have gone, so it got stinking hot and emitted a faint pop sound...I thought it would be an ex-transistor after that, but careful measuring revealed that it still worked. Sweet.
The reason for all this mucking around was that the LCD backlight had been on for a whole year now, continuously, drawing a good 250mA. It lights the living room up a fair bit which is annoying at night and attracts all kinds of flying bugs. Now I've overhauled the software-side (lcdraptor and a homegrown jukebox in perl) to go dark when not doing anything useful and added all kinds of things to them and lirc-xmms on the way.
Well, looks like my solder-fu is improving. Just ripped the dead Ultra1 power supply apart, to look for bad or dead caps - not that I expect a 8-10 year old Sun PSU to have used crappy caps, but something must have died and electrolytic capacitors do have a limited life time by design. Found two somewhat seedy looking small capacitors (100uf and 22uf) in the secondary section, replaced them and contrary to my expectations the PSU works again :-) Amazing tech, this thing; prodding it with the voltmeter showed that it has two primary stages, one that sports a healthy 400V DC. I was somewhat careful not to touch these solder posts...