Re: IIgs problem...

[dempson@actrix.gen.nz (David Empson)]

Labelas Enoreth <labelas@hotmail.com> wrote:

> In article <1dpozut.1g5mur5hvtueN@dempson.actrix.gen.nz>,
> dempson@actrix.gen.nz (David Empson) wrote:
> 
> > I saw in the earlier article that you mentioned 41256-15 RAM from a IIe.
> > In theory, this should be OK on a IIgs.  150 ns RAM is the slowest type
> > that can be used in the IIgs, assuming the card is able to handle it.
> > Many cards use 120 ns RAM (or faster) to improve the timings.
>
> Wow. Now that I'm looking at the card, there's a couple -12 RAMs in there
> too. They look identical to the -15s, except for the fact that they're
> 120ns obviously...I guess I didn't look very hard originally...I guess,
> this could be causing a problem, no?

To minimise problems, you should use identical RAM within each bank.
Mixing 150 ns and 120 ns RAM should be fine (as long as each "row" of
eight chips is the same speed).

Getting on to your followup:

> Moved the chips around again, now the card is laid out so that the top row
> is 16 150ns chips (8 soldered on) and the bottom is 16 120ns chips.
> I just don't have another 16 150ns chips to put there.
> Anyway, here's the thing. Startup without card in...computer works fine.
> Startup with card with no jumpers (only first 8 chips in upper bank used,
> right?)...works fine.

OK so far.

> Startup with upper jumper on (upper bank used, right?)...works fine

This combination is illegal.  Assuming the card works sensibly, it will
allow the card to select between the top and bottom row, but not between
the left and right halves.  This will leave holes in the address space,
and any extra RAM available will be ignored, since it isn't contiguous
with the motherboard RAM.  In effect, it is the same as no jumpers (256K
enabled).

> Startup with bottom jumper on (bottom bank used, right?)...works fine

This is actually enabling both banks in the top row on the card,
assuming Rubywand's FAQ is correct.  512K of RAM is added to the
motherboard RAM.

> Put both jumpers on, and wham. There's the errors and crashing.

Implication: a faulty RAM chip in the bottom row, or a card fault
affecting the bottom row.

Try doing the following:

1. Connect the bottom jumper only (so the top row is enabled and the
bottom row is disabled).

2. Swap the eight chips from the bottom left to the top right bank, and
try the card.  If it crashes, then one of these eight chips is faulty.

3. If no problems, try the chips from the bottom right bank in the top
right bank.  If it crashes, then one of these eight chips is faulty.

If both combinations work, then the card itself has a fault with the
bottom row.

If you get a crash after step 2 or 3, then you'll have to start swapping
individual 120 ns RAM chips until you find a good combination.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand