Hi all,

My FS-A1ST, which has 512KB RAM, strangely began to count only 64KB of RAM on boot.

I did some tests using my Mega-Assembler cartridge (aka Simple3) and the results are the following:

On the upper 16 pages seem to be normal.

The lower 16 pages, have a very weird behaviour:

The pages are repeated on each 64KB, almost as it happens when there are only 64KB of memory-mapper.

But if i select the frame-2 (8000h) on page-1 and the frame-1 (4000h) on page-5, instead of the contents being the same, only the lower nibbles are equal. The higher nibble has another weird behavior:

- If I write anything on the frame-1, the frame-2 reads the higher nibble as 1111. But it is read normally by the frame-1.

On the other hand, if I write anything using the frame-2, the frame-1 reads the higher nibble as 0000. But it is read normally by the frame-2.

Does anybody have any idea of what may be happening?

If the 44256 DRAM CIs are damaged, I'll only have the option to remove all of them and upgrade the A1ST ram to 1MB using a 30 pin SIMM module.

I'm looking for good documentation on how to do this, but the only ones I've found was those:

1) 1MBRAM.PMA, from
http://www.funet.fi/pub/msx/utils/misc/freewar2.pma (maybe it's in one of the other 2 disks)
- Problem: Japanese documentation, very hard to read

2) turbor1mbe.pdf
http://www.funet.fi/pub/msx/mirrors/hanso/hwdoityourself/turbor1mbe.pdf
- Problem: It seems to contain a lot of mistakes

Does anybody have an DIY receipt for upgrading the A1ST RAM to 1MB using a 30-pin SIMM module? It would be very welcome.

Best regards,
FRS

(in the first place check if upgrade is correct)
Required(from hansO web page)

· 2x 44C256 RAM IC's
· 2 SMD-capacitor 100 nF
· 2 SMD-weerstand 100 Ohm
· 1 resistor 10 kOhm

Follow the next steps:
1. Solder the RAM IC's in the empty sockets IC31 and IC33.
2. Solder the SMD capacitors 100 nF on the empty locations C138 and C140.
3. Solder the SMD resistor 100 on the empty location R55.
4. Solder a 10 kOhm resistor on the empty location R41.
5. Solder a SMD resistor 100 Ohm on the empty location R229 on the bottom of the PCB!
6. Start the turboR ST and it should show 512KB!

If I were you and upgrade is correct:
a) desolder 44256 dram chips
b) put sockets for it
c) get new 44256 ram chips, you can get it in old PC VGA cards.

Upgrade to 1Mb is very hard and dangerous. You'll need to build a new memory mapper.

>If the 44256 DRAM CIs are damaged, I'll only have the option to >remove all of them and upgrade the A1ST ram to 1MB using a 30 pin >SIMM module.

Quote:

Upgrade to 1Mb is very hard and dangerous. You'll need to build a new memory mapper. >If the 44256 DRAM CIs are damaged, I'll only have the option to >remove all of them and upgrade the A1ST ram to 1MB using a 30 pin >SIMM module.

Or ...

http://www.passionmsx.org/modules/xcgal/displayimage.php?pid=1232&album=97&pos=8

http://www.msx.org/forumtopic7669.html

Or you just replace the old Ram IC's with new ones.
You can stil buy them, a bit expensive but still on the market.

see on Hans Otten : http://www.hansotten.com/msxnews.html

schema for the 1 Mo Memory for ST and GT

it's the schema of "turbor1mbe.pdf"

but before replace Ram check R41 R229