Re: Notes on Cleaning and Repairing an Apple II Plus

[dog_cow@macgui.com (D Finnigan)]

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...)

>> 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.

> 
> 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.

> 
> 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. :-/

> 
> 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.

> 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!

> 
> 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.

-- 
Mac GUI Vault - A source for retro Apple II and
Macintosh computing.
http://macgui.com/vault/