HB-F1XD Japanese MSX2 - Replace V9938 with V9958?

Page 2/8
1 | | 3 | 4 | 5 | 6 | 7

By Colemu

Hero (535)

Colemu's picture

08-09-2012, 18:05

Thanks Jipe. I don't know if this part is going to be a little out of my league.

I'll start with the VDP replacement and then think about the Basic 3 issue.

Doesn't look like it's a straight rom replacement job.. Sad

By Colemu

Hero (535)

Colemu's picture

08-09-2012, 20:05

Almost forgot the 128k issue.

Am I able to piggyback two extra 32k ram chips, or this this just too much to hope for Question

I have a memory mapper, but some games just refuse to work with it oO

By RetroTechie

Paragon (1563)

RetroTechie's picture

08-09-2012, 20:27

Schematic shows this machine has the S-1985 inside, which includes a 512 KB memory mapper. The pin with the highest address line (MA18) also has a keyboard-related function (KBDIR), which doesn't seem to be used here.

So it should be relatively easy to put 512 KB RAM in this machine. But I don't know of any ready-to-use instructions or schematic how to do this. Are there any empty ROM sockets / space for those on the mainboard? If so, it shouldn't be too hard to connect a 512K*8 bit static RAM chip. Otherwise you'd have to piggyback such a RAM chip onto a ROM (or use 4 pieces 256K*4 DRAM chips, which might not be so easy to connect).

By Colemu

Hero (535)

Colemu's picture

08-09-2012, 22:23

looking at the mainboard now. It has 2 x 32k ram (TMM41464AP-12) IN IC 16&17. No space for extra RAM on the board unfortunately.
Seems like they're 4 bit ram. I'm wondering if these can be replaced with "bigger" ones?

Would these work? Question
http://www.ebay.co.uk/itm/320865615781?ssPageName=STRK:MEWAX...
or these in piggyback:
http://www.ebay.co.uk/itm/160876678065?ssPageName=STRK:MEWAX...

By Colemu

Hero (535)

Colemu's picture

09-09-2012, 15:50

I'll presume these are a no go.
Thanks all....

By igal

Master (216)

igal's picture

09-09-2012, 16:00

By Colemu

Hero (535)

Colemu's picture

09-09-2012, 16:05

Great, will these just piggyback the existing RAM Igal?

By RetroTechie

Paragon (1563)

RetroTechie's picture

09-09-2012, 17:58

For 512 KB, you'd need 1 of these: AS6C4008-55PCN 5V compatible, 512K*8 bit SRAM in DIP housing. Other distributors have similar parts.

You'd solder it on top of a ROM with a few pins bent sideways & connected elsewhere. So if you'd use this part & are planning a 2+ upgrade, you might want to change the ROMs first, and then solder such an SRAM on top. This would be most reliable method as you'd buy a brand new part, and static RAMs are generally easy to get working as compared to DRAMs. In this case, disadvantage is having to stack it on top of a ROM (or a sh*tload of wires).

Other option - 4 pieces of 256K*4 bit DRAM (type 44256 or equivalent): 1 2 3 4 - probably many more sellers, but all New Old Stock so you'd build with 20+ year old parts. Sometimes you can find these chips on really old video cards or XT/AT era motherboards. Also it's difficult to test these chips before use.

You'd connect these by soldering them into original DRAM locations, roughly 1:1 but re-routing some pins. Then stack a 2nd set on top, and connect control signals. But I'm not sure if you can connect these in your machine without adding additional logic. About the only advantage I can think of is you'd use the original DRAM locations & thus no piggybacking anything on top of a ROM.

To be honest: if you attempt a memory upgrade at all, I don't see why you'd even bother for less than 512 KB. In any case you'd need decent soldering skills since at least you'd need to pick up several signals from the S-1985 whose pins are spaced very close. Not a beginner's job!

By Colemu

Hero (535)

Colemu's picture

09-09-2012, 19:56

thanks.

Maybe I'll concentrate on the Rom replacement first then, this seems a little more complicated. I'm not bad with a soldering iron, but my knowledge of the MSX hardware is a little limited at the moment.

I only see one ROM chip which is identified with BASIC. However, I am aware there are 3 roms to replace to upgrade (Bios, Dsk, Ext). I have obtained the HB-F1XDJ versions of these as this is the 2+ version of my computer. Do they all fit into the same rom? if so, which eprom would I need? I also have 27c400 eproms at hand....

Just checked the Basic chip is LH531067, the 27c400 are a different size, however my 27c256 eproms are an exact fit (28 pin). Is this eprom a feasable replacement?
Another one in the FDC section is TMS2793NL, MAS 74503 (20PIN, same size as my 27c400 eprom), is this the disk ROM?

Is this enough:
As the 27c256 is 32k, transfer the Basic from HB-F1XDJ to this eprom. Replace the LH531067 with this eprom. Sounds the most straight forward way, will it work? (in theory)? Question

By msxholder

Champion (394)

msxholder's picture

09-09-2012, 22:01

No this don't work the mask rom contains mainrom subrom diskrom in pages of 16k or 32k
In the f1xdj the slots,subslots and pages are mixed trough logic so only one rom was needed
You need to have an replacement with main sub disk in exact same sequence

Page 2/8
1 | | 3 | 4 | 5 | 6 | 7