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Re: Notes on Cleaning and Repairing an Apple II Plus

D Finnigan wrote:

Michael J. Mahon wrote:


D Finnigan wrote:


I obtained an Apple II Plus yesterday. As is typical of me, a few hours
after I plugged it in and verified it to be working, I managed to break
it.
Here are my notes from cleaning and repairing it, for future benefit. Ah,
experience. What a teacher.


Yep.  Good judgement comes from experience, and experience comes
from poor judgement...  ;-)




Yes, but sometimes I just wish that I could get experience with someone
else's equipment, or with equipment for which I had many spares. (Oops,
broke one; go fetch me a spare and we won't do *that* again...)


This is part of the "practice on things that don't matter" rule.  ;-)


It had a gold power supply
with
a serial number in the 100k range.



I checked again last night from a photo, and it was actually lower, in the
81k range. I don't have the Apple II here, nor do I have the sheet on which
I wrote the serial numbers, so it's just my memory.

Actually, I've been checking various dates, and they don't seem to line up.
I already said the motherboard date reads as an early 1979, maybe Feb. But
there's a date stamped on the case that looks like Oct 2 1980, and some of
the chips on the motherboard seem to have date codes from 1980. I wonder if
the motherboard is manufactured earlier, then populated with ICs later, and
then finally put in a case.


Exactly.

The manufacturer procures chips from various sources and in various
quantities, so some stock is older than others.  When a board is built,
it will contain the "current" chips in stock, but, of course, none will
be newer than the build date.  ;-)

If you inventory the chip dates on a board and find a distribution of
dates, the build date is most likely not long after the latest chip--
unless there are a few chips with significantly later dates than the
rest.  In that case, the later chips were probably replacements made
after the build date.


Right--your repeated operation of the keyswitch mechanically abraded the
oxides on the surface of the switch contacts.

The best way to keep a keyboard *electrically* clean is to use it
regularly to prevent oxidation from building up.




I wonder if spraying WD-40 into the keyswitch would work well.


Dangerous.  WD-40 contains ingredients which can cause some plastics
to expand.  It is also *not* a contact cleaner nor a de-oxidizer.

Avoid using *any* liquids on keyswitches unless nothing else works,
and then use only electronic contact cleaner/lubricant, and very
sparingly.

Once you spray or wash something into a keyswitch, any non-volatile
components (including dissolved dirt) will stay there forever--unless
you enjoy disassembling keyswitches and manually cleaning them.  ;-)


I recommend doing an unfamiliar disassembly on a large table covered
with newsprint or something like it, so that errant pieces are easily
noticed. 


Apparently, the dining room table wasn't large enough! I managed to get the
screws separated out so that I could put them back in the right groups
(power supply, motherboard, keyboard, etc.) I just slipped up with those two
space bar thingies. With my luck, they've probably flown off out a window
somewhere. :-/


I'm betting they will turn up--hopefully before the next vacuuming.  ;-)

I've sometimes put a handkerchief "pouched" between vacuum cleaner
hose fittings, then vacuumed an area (being careful to hold the "pouch"
upright inside the fittings before turning off the airflow.  Careful
opening of the fittings and perusal of the contents of the pouch has
revealed the missing parts (and much else ;-).

It's easier if the missing parts are magnetic...then a sweep with a
strong magnet usually does the trick.


You were quite lucky--that cable inversion can do some exciting things!




So I've heard, and I was worried that I had in fact fried either the drive
or the controller card. In my haste, I even pulled the card out while the
power was still on, (what was my problem?! I probably needed more sleep) but
the Apple just reset.


You are indeed golden!


If you've just washed the keyboard, the encoder is *not* the most
likely problem (as you discovered).

Nine times out of ten, the problem is with something you just did,
not something else.  ;-)




Well, my thought was that maybe the moisture lead to it getting zapped. I
even tried plugging the keyboard cable in the other way around to see if
that was the problem. It wasn't, but it made an interesting pattern on the
screen when I turned the Apple on!


That's always a possibility, but the thing to do, then, is to wait a
*long* time (2-3 days?) so you're *absolutely sure* that no moisture
remains, and 1) try again--all may be well, or 2) then try replacing
the encoder, since now you can be reasonably sure that any moisture
path that killed the first one won't kill another.


Early ][+ main boards did not have sufficient isolation of the color
burst, so enough of it leaked through to trigger sensitive monitors to
go into color mode.

Later revisions (7 and later?) had a mod which fixed this leakage.
So if you have a pre-rev 7 (?) board, the over-eager switching to color
mode is authentic.



Something gave me a strong impression that I do not have a Revision 7 board,
and that was the presence of three 16k memory select blocks. I'm guessing
that it's revision 6 or something, because it has the single wire-wrap video
pin, as well as the color-killer transistor. And it also has all of the
chips to the right of the 6502 CPU. The copyright date below the 6502 is
1978. Unfortunately, I can't check the motherboard part number at the
moment, so that will have to wait.


Bingo.

It is definitely pre-rev 7.  You can either use the proto area in the
lower right corner of the board (slots on top) to wire up the enhanced
color burst gating that was pre-installed on the rev 7 board, or you
can try a different color monitor, hoping for one that is less sensitive
to color burst leakage.

Or you can use a monochrome monitor wired directly to the video output
jack and ignore the color monitor when using text modes.  (That was my
standard mode of operation).

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."