Re: Trying to fix an Apple II+ : blue & orange colors "sparkle" & cap with only one connection

[Michael J. Mahon <mjmahon@aol.com>]

eccofonic <eccofonic@charter.net> wrote:
> I pulled out my old Apple II after 6 or 7 years of neglect... it had
> always been a little flakey, but when power was applied, it wouldn't
> boot. Just a garbage screen. I cleaned the board and any dirty chip
> contacts, and now it is booting fine.
> 
> Except...
> 
> Part One:
> 
> When I took the board out of it's case I noticed a 16v 10uf capacitor
> *underneath* the board with one side soldered to power connector pins
> 1 & 2, which are both ground. The other side of the cap isn't
> connected to anything???
> 
> I think I have the board revision after they removed the RAM size
> select switches. It says "820-044-01"...
> 
> There is a 10uf cap labeled "C17" in the "Apple II Reference manual
> addendum" schematic, but it is connected to pin 3.
> 
> Is the other end of this cap not supposed to be connected to anything,
> or maybe "screwed down" to the die cast metal plate in the back
> area... by the expansion card slots?
> 
> Part Two:
> 
> When the computer is turned on from a cold state... if it is booted
> immediately to a graphic containing blue & orange colors... these
> colors are purple and green instead.
> 
> Gradually, these areas start to "sparkle"... imagine hundreds of  dots
> randomly flickering brighter...
> 
> And the blue and the orange colors "fade" in.
> 
> But the "sparkles" remain, mostly in the orange areas.
> 
> I read that Woz devised a circuit to add more color to the original
> Apple II, so maybe this the culprit?
> 
> Thanks in advance for any info you can offer!

Both leads of any capacitor should be connected. It sounds like the ground
side is connected. If this lead is the lead marked "negative" on the
capacitor, then the other lead should be connected to either the +5v or the
+12v line. Since decoupling on the +12v line is less important, I'd expect
the positive lead of the capacitor(s) to connect to the +5v bus. 

WRT the intermittent color set, since it only fails when the computer has
been off, I suspect a temperature-sensitive poor connection/contact in the
"second color set" circuit. Look it over very carefully for a poor
connection or contact, or a cold solder joint. Gently probing the
connections in this circuit with a non-conductive probe may quickly reveal
the intermittent node. Fixing this intermittent connection should restore
normal operation. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon