Re: IIGS 1 meg RAM card - trouble-shooting?

[Rubywand <rubywand@swbell.net>]

stephen e buggie writes ...
> 
>      I have a IIgs RAM card that jams up the computer. No damage, but when
> its in the slot, a get a large-square "checkerboard" pattern on the
> screen, and nothing boots up.  Not even the self-test will activate.
> 
> I also have another flaky IIgs 1 meg RAM card, and propose to socket-ize
> the controller chips to get one wroking card out of two dead ones.
> 
> But WHICH CHIPS should be tested first?  Installing sockets is no picnic
> so I want to minimize the number that have to be done.   Neither card has
> any obvious physical damage.   (The other card always gives an error of a
> bad chip in a particular chip location, regardless of which chip is in
> that socket.)
>
 ....


     The standard Apple IIgs 1MB Memory Expansion card-- all of the ones
I've seen-- comes with 256kB of RAM installed (8 IC's in the upper Left
row). So; one possibility for a bad 'bare board' is a bad RAM chip.

     Finding two bad 1BM Mem Expansion cards which cause a primary
system failure (the "Checkerboard of Death" as Anthony Politz would say)
is remarkably bad luck. One thing to make sure of is that the mem size
jumper is set correctly: 


     For 256kB, the top left 8 sockets (i.e. the left half of the top
row) should be filled. No jumpers should be placed on the pins near the
lower right end of the board.


XXXXXXXX--------
----------------
                         O O (no Jumpers)
                         0 0


     For 512kB, the entire top row of sockets should be filled. The
bottom 
pair of pins should be jumpered.

XXXXXXXXXXXXXXXX
----------------
                         O O
                         0-0 Jumper bottom pair


     For 1MB, all sockets should be filled. The top and bottom pairs of 
pins should be jumpered.

XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
                        O-O Jumper top and bottom pairs
                        O-O 


     If the jumper is set correctly for 256kB (i.e. no jumper) and the
board is unpopulated except for 8 mem chips in the upper Left row, then,
something else to check is that your Control Panel settings do not
expect to set up a big RAM disk.


     For an Apple IIgs 1MB board with 256kB plugged into the Memory
Expansion Slot, there is not a whole lot which can go bad. (When two
boards show up as "bad" on a GS, you start to wonder about the GS, its
settings, the booted software, ... .

     Since, evidently, the board does not short the power supply, you
can most likely eliminate a shorted bypass capacitor. _If_ there is a
bad IC on such a board, the first one to pull is, probably, the 74F139.
The '139 series has popped up as the faulty IC in other places. My
second choice would be the 74F245.



Rubywand