All,
Got a Mac Classic, swapped non-functional hard drive,
installed RAM, nearly got it working for my 10-year-old. But....
First pass, no sound out. Not speaker, not headphone
connector. Wait, if you hold your ear right up against it, you hear a
*little* bit. Hm.
Second pass, a week or so later, won't boot. Hmm.
Opened it back up, looked over everything ... what's this?
There's some stuff on the digital board. Wonder what could leave an
oily stain, and how it got there in the first place without leaving
tracks on the inside of the case, the CRT, the disk drives, etc.
etc.? Well, won't hurt to clean it off, I thought ... then the penny
dropped and I realized that there were *three* little islands of
gunge, and they were centered on the three groups of what look like
my favorite nemesis .... capacitors!
What a suprise...
<gnashing of teeth>
Many q-tips and much isopropanol later, it boots, but it's
still quiet - too quiet - and I have a bad feeling about how long
it'll keep running before I have to clean it again. There's a bit of
corrosion on one lead of the sound chip, but I can still hear a very
very faint edition of the sound it's supposed to make.
The Classic has a surface-mount digital board. The components
I suspect are metal can devices, lots of them with the same marking
(which I neglected to write down) and one different. Each has a tiny
flat plastic-looking isolator or something between it and the logic
board.
The 'gunge' is probably the electrolye from an aluminium electrolytic
capacitor. Needless to say the capacitor doesn't work well without it,
and it's entirely possible that the lack of sound is due to a defective
cpaaicotr in the signal path.
1) Is there a preferred solvent I can squirt under those things and
the sound chip that'll pick up capacitor gunge (or whatever it is)
better than Isopropanol? Is the old standby dihydrogen monoxide a
good bet? (I have plenty of that.)
2) If (sigh. When) I have to pull those things off, I will need a
hot-air soldering station, correct? My thought is, cut up an aluminum
can to make an air dam isolating the cap. from the rest of the board,
then blast it with hot air until it flies off or vaporizes. Is that
close to right?
I would want to remove all the suspect capacitors, clean the PCB, and fit
noew ones.
You do not need a hot-air soldering station. They only have 2 leads. If
you remove as much of the solder as you can with desolder braid, and then
heat one lead at a time you will find you can pop them off the PCB. To
fit new ones, posiitoned them (and make sure they are the right way
round) and then solder them with a fine-tipped soldering iron and thin
solder.
It's not particularlly difficult.
3) How do I get replacements, and how do I slap those back down on
the board? Is the code on the top all I need to order more?
That depends on what the markings are :-) You need to know the
capacitance (in microfarads), the working voltage (you can use one that
sensibly higher than the existing one -- if the existing one is 16V, then
you could fit a 25V one with no problems) and the physiucal size (so it
will fit the pads on the PCB).
-tony