Help hacking and restoring AX-350II sakhr

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By maxis

Champion (502)

maxis's picture

20-01-2018, 09:13

ali6x944 wrote:

I think I will start by increasing the RAM, by populating IC312, IC313, IC316, IC317 on the main board.
https://drive.google.com/file/d/182N0uKH1QnZah0V5CQSrkxzHRpJ...
Also I'm curious to know the chip on this riser board, I googled the part number of XD025C0-052 and no immediate results, but I think it is a costume mask ROM requested by Al-Alamiyah for Arabic characters or Arabic MSX BASIC, I would presume...

You will need to find out how to switch the memory mapper to 256K. Now it's configured in 128K. I would propose that you will start with the config change before you put the RAM in.

By Alexey

Paragon (1350)

Alexey's picture

20-01-2018, 14:24

On YIS805 board there was a solder jumper to configure 128 or 256kb. So this board has something similar for sure. What is under that separate board? It's unlikely that basic, bios and disk rom were put into a single rom chip.

I am now tempted to breed a hybrid of this arabic MSX and my russian YIS503. The case cover and keyboard can be from a russian model, the rest could remain from the arabic one. Maybe a video module change is needed. But in the end I can get a proper YIS503 with a built-in drive and 256kb or ram...

By Wild_Penguin

Champion (414)

Wild_Penguin's picture

20-01-2018, 16:38

ali6x944 wrote:

Also fast question, can the keyboard key-caps be removed?
Mine are a bit dirty...

In short: no. They were not designed to be removed (contrary to some very similar models such as the Yamaha computers).

Long answer: If you just try to lift them, there are some plastic parts that will break. But they can be removed with some tools and patience. I needed to do that since on my AX-350II, some keys were not working at all since thay had some sand etc. inside them! But, the whole process is so tedious that I've never come around to it (I "refurbished" just the most important keys, but all of the keys are in a need of a similar overhaul).

In case you break some keys, they can be fixed with some thread and superglue; but this is fiddly and will require some patience.

I have some pictures ... somewhere. I'll try to find them and post them here if I do. In the meantime, you have been warned Cool

By Wild_Penguin

Champion (414)

Wild_Penguin's picture

20-01-2018, 18:20

Ok, here are some pictures.

Disassembling the keyboard is somewhat straightforward (remove screws etc), except for the keys with LEDs. Those need to be de-soldered before the keyboard can be disassembled properly (IIRC this part is similar to other Yamaha computers with similar keyboard and described in their SM). No pictures of this part, sorry (IIRC I might have taken them but it was nearly a year ago, and if I did, they are lost somewhere).

EDIT: The keycaps come off the plate they are attached as in the CX5M SM linked previously. However, the actual mechanisms are different (probably cheaper to construct?), and only CAPS and CODE caps are removable just by lifting them off as in the SM. As for the others, see below...

The keyboard is a membrane keyboard:

With springs housed inside the assembly the actual keycap is attached to (this is just the "top" part!):

The whole keycap assembly is quite easy to remove from the plate; however getting to the part with the spring (which will also collect dust, sand etc. and make the mechanism not work properly) is not easy, as the other half of the assembly will get easily broken. Here is a broken and an intact problematic part:

The easily broken part is under the keycap and nearly impossible to get to. If you just lift the keycap, it will break! However there are small holes at the bottom of the assembly that can be used to bend the flaps away so that the assembly does not break. Here I am trying to remove the "halves" from each other with the help of partially straightened paper staples (result: Success!):

Here I am using some very strong thread (bear thread) to wind around the broken parts. Aftgerwards I soaked the thread in cyanoacrylate -based superglue. (I used more laps than in the pictures). Result: The keycap does stays inplace now! The fixed keycaps are indistinguishable in use from the originals, btw.

There are more pictures in the album (from different angles etc.)!

By hamlet

Scribe (1518)

hamlet's picture

20-01-2018, 18:31

What a nice "how to"! Thanks Wild_Penguin!

By ali6x944

Resident (38)

ali6x944's picture

22-01-2018, 05:17

Incredible how-to Wild_Penguin! Done like a boss, Thanks a lot for all the info Smile
Also I have finished cleaning the keyboard module.
Maxis have mentioned that the AX-350II has the YIS-805 circuit with few modifications, dose anyone have the schematic or service manual for the YIS-805, so far reading the CX5MII showed clear differences in board layout and system upgrade-ability
For example the bord seems to have empty unpopulated spaces for extra ram perhaps, but in the manual it show no hint of 256k model or upgrade...

By ali6x944

Resident (38)

ali6x944's picture

22-01-2018, 10:03

Also I must note that the main board is containing multiple chips that are note in the schematic in the CX5MII service manual...

By Grauw

Enlighted (6676)

Grauw's picture

22-01-2018, 12:56

Yeah, there’s (at least) two versions of the CX5MII board, the CX7 one and the XB300 one. E.g. the description of the CX5MII conversion to MSX2 unfortunately references the XB300 board.

But if it’s the same board as the 805 (slightly odd, since the form factor is quite different), maybe this service manual will be of use: http://msx.hansotten.com/uploads/files/ax500servicemanual.pdf

The YIS-503IIR service manual is scanned as well, though I can’t find a download link...

By Alexey

Paragon (1350)

Alexey's picture

22-01-2018, 15:23

Just checked by old docs. In order to get 256kb on a 128kb YIS805 (also AX500), pin 13 of IC314 (LS139) needs to be connected to MA17 signal instead of GND.

This is done by a jumper J305 that can be seen on this photo:

https://www.msx.org/wiki/images/6/66/Yis805128r2f.jpg

For AX-350 there should be a similar way. The IC306 (corresponds to IC314 on AX-500) is there, but I can't see on the photos where pin 13 is connected to.

By Alexey

Paragon (1350)

Alexey's picture

22-01-2018, 15:33

Btw on the board between IC305 and IC308 there's something like a jumper marked as -- J --. Assuming the LS670 chip is a part of the mapper, it could be the jumper to configure for 256kb. But this is an unprofessional guess and I would not recommend to mess with the board until a professional says so.

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