MSX Memory Issue

By Shinobi

Expert (125)

Shinobi's picture

09-08-2020, 02:57

Hi
I have an MSX AX-200 with no keyboard...after making a PS/2 keyboard works for it I could do some experiments:
1-MSX displays 12431 bytes free (it displayed before 28815 bytes free and before that it displayed 12431 bytes too, so it is changing as if there is some problem)
2- after entering into basic in international mode (pressing ctrl at boot) I made some statements to write to some addresses between 8000 and BFFF (the first 16kB bank)..I read it first and see it contains some values...I write some other values on these addresses...when reading these addresses again...it gave me the old values as if it didn't save my values..
3-made the same procedure in point 2 to addresses from c000 to ffff .. this time it saved my values ok...
4-then I went into Arabic firmware..from msx dot org it is from 4000 to bfff...so I repeated procedure in point 2 to 0000 to 3fff .. it didn't saved my values and returned the old values...
5-repeated the same procedure on c000 to ffff...it saved my values...

here is a picture of my memory cart:
https://imgur.com/a/Ls4jTvr

is there a problem with all memory chips or some of them??
is an 8 bit saved in all 8 memory chips as a bit in each chip??

here is msx dot org link of msx ax-200 for further info
https://www.msx.org/wiki/Sakhr_AX-200

I don't have any ram expansions to check..no cassette interface cables...I have pigmock game cart and it works...
I will be happy to fix it rather than buy a ram cart...
thanks

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By Shinobi

Expert (125)

Shinobi's picture

10-08-2020, 03:32

come on people need some help here..at least a suggestion

By Eugeny_Brychkov

Paragon (1166)

Eugeny_Brychkov's picture

10-08-2020, 10:16

I confirm that 12431 is a size of the RAM available when BASIC boots with 16K of the RAM.
You have something faulty, and machine needs to be repaired. It is not possible to say what is faulty without diagnostics and replacements. May simply be a bad contact or deteriorated soldering.

By Shinobi

Expert (125)

Shinobi's picture

11-08-2020, 02:33

CAS2/E active low ... no continuity between MSX engine CAS2/E and RAM socket CAS2 pin .. while all other MPX RAS WE there is continuity between them in RAM socket and MSX engine ...
could that be the reason that my ram is giving me 12318 when it should be 28815..
in Yamaha YIS503IIR which is closest relative to MSX AX-200 .. it says tha CAS RAS MPX WE should go from MSX Engine to RAM Socket .. and the socket number is even the same CN314

By Shinobi

Expert (125)

Shinobi's picture

15-08-2020, 00:58

Solved: for any one to read shall find this useful
in MSX AX-200 Cas2/E and Cas3 goes into AND gate then to memory socket
At first I didn't know it since the YIS russian computer I used its schematics showd cas3 not connected and cas2 goes straight to memory socket...so I shorted cas2/E pin of msx engine to cas2/E of memory socket...turned on machine...a black screen
took the short wire out..turn on machine...it workes...I think there was an issue with AND gate chip was fixed by this.