Re: Trying to fix an Apple II...

[Jeronimo Pellegrini <jeronimo@dcc.unicamp.br>]

:: On Thu, 15 Apr 1999 18:50:48 -0500, Rubywand <rubywand@swbell.net>
said: 

> Jeronimo Pellegrini writes ...

Hi!

>      Could be. You could remove the pot and check resistances to
> determine the value needed for a replacement. Even if one of the
> terminals is blown, you can use the remaining two to get the max
> value. The pot swapped into an Apple 'Disk ][' drive (to have an
> external adjustement) is 5k; but, there is no guarantee that a
> different drive would use the same value. 

I don't trust my ability to solder it back... So I just measured it on
the board. I know the values could change, but... The fact that the
resistence changes wouldn't be affected. And it goes from 0 to 50k.

>      You could open the drive and clean the head using alcohol on a
> cutton swab. The head will be on some sort of slide rail and it will
> be facing up. 

The head is usually white. It was brown. Some disks were doing
that. Someone told me that there's a layer of something before the
disk magnetic layer, and that if this layer was perfurated, material
from inside could leak... He suggested that I clean the disks with
cloth. I did - and oddly enough, it works! I could recover 3 disks
already.

But even with a clean head, the reported speed doesn't change when I
adjust the minipot. The drive's behaviour changes, but not the speed
reporteed by software. Strange.
 

>      My experience with A2 clones is just about zero. Perhaps
> someone here knows more about a clone which displays "COMPUTER" upon
> start up.

>      If it lets you enter upper and lower case, it is likely to be
> at least an early IIe clone. If it lets you run "128k" software and
> double-hires games (like King's Quest) in 16 colors, it is an
> enhanced IIe clone. 

Well, I have a 128k expansion card. It's not like the 16k expansion,
from which a cable would go into the mother board. It has 8 memory
banks, and you can switch to use any at a time. There are 3 leds in
the board that tell you which bank is being used!
I use ramdisk in both CP/M and DOS, I can backup disks with only one
drive, and not have to swap disks more than once, etc.
I can also move DOS to the memory card, so it becomes "almost
invisible"...

Now... I don't remember having read or heard anything about "double
hi-res" before...

>      Good idea to experiment! I rechecked the old II+ schematic and,
> as you suggested, it does use a 555 to cause blinking (flashing)
> characters to blink. The condition is that character bit 7 be 0 and
> bit 6 be 1-- a blinking space cursor would just need to be a
> $60. Sorry about the mistake. So, you may be looking for a 555, 556
> (dual 555), or 558 (quad 555) which needs to be replaced or, maybe,
> just pulled and re-socketed to make a good contact. 

I replaced both, but the problem persists.
I wish I had the schemes... I could check the places where things
could be wrong.

Not only the cursos doesn't blink (it remains invisible), but also
flash mode doesn't work. And inverse mode works, except for lower case
letters - then it shows other ASCII characters:

! @ # $ % etc...

This is strange...

Well, any ideas are appreciated!

Thanks a lot!

Jeronimo