Re: IIGS memory error

[apple2pd@garp3.icaen.uiowa.edu (ground.ecn AppleII Librarian)]

In article <1f9g4mg.cqqicu12qqdw8N%dempson@actrix.gen.nz>,
David Empson <dempson@actrix.gen.nz> wrote:
>ground.ecn AppleII Librarian <apple2pd@garp3.icaen.uiowa.edu> wrote:
>
>> When I run the Claris memory test (MemoryCL) from AWGS on a Rom3 with 1Meg
>> Apple memory expansion board, I get a memory error at $180582 .
>
>Is the same location reported each time you run the test?  I'll assume
>that it is.
>
>$180582 is $100000 + $80000 + $0582.
>
>The motherboard has the first 1 MB ($100000), so the error is on the
>memory expansion card.  The card has rows which hold 256 KB ($40000)
>each, so the fault is in the "third row" on the card.
>

Thanks to David for his help and suggestions.  I took a slightly different
approach to isolate two bad chips.  I haven't determined memory mapping
for the 1Mb Apple expansion card yet.  Board with 256K shows memory to
$12000 ???, with 512K memory goes to $16000 ???.  So I think MB = $80000,
plus $40000 per 256K.  (I am trusting my memory here so I may be wrong.
In fact, this can't be right).
  
Using the system monitor (from basic call -151), I
could see that at 18/0582 I had a chip with hi-bit stuck on '0' (80=00,
FF=7F) and the same at 18/05a2.  But a memory move from one 256 byte page
to another gave me really screwy values (lots of 7D ).

Anyway, I did all my testing with 512K memory.  First I removed all 24
chips, then used groups of 8 until I had a group of 8 that worked.  Then I
swapped in four chips at a time to find a good groups of 4.  Then 2 at a
time from the bad groups of 4 to get good groups of 2.  Finally I had two
groups of bad 2 chips.  Then I found the two bad and two good chips.
I used the memoryCL pgm from Claris AWGS for memory tests.

So now I have 22 good chips :-)  and 2 bad :-(  I can't find a local
source of DRAM but when I get some good 4256 chips, I will provide
a memory test with 1 bad memory chips at each of the 24 locations
(UA9-UA16, UB1-UB16)  (UA is top row, UB is bottom row).  This should help
others figure out where a bad mem chip is located.  I just need to locate
at least one good chip to start, but obviously I want two good chips.
Thanks goodness it wasn't one of the 8 soldered chips.

  --Steve

-- 

 --Steve  (apple2pd@ground.ecn.uiowa.edu)