Philips NMS 8220 RAM upgrade to 128k - Which chips to buy?

By lightman

Supporter (6)

Аватар пользователя lightman

12-04-2016, 00:43

Hello MSX fans,

as the title suggests I want to upgrade the RAM of my 8220 to 128k. I've read the corresponding Wiki article and also downloaded the PDF document describing the modification from bas-ditta.info so I'm familiar with the general procedure.

My question is: What exact type of 41464 RAM chips do I need? I've googled for "41464 ram chips" and got all sorts of results for different chips with 16 or 18 pins, 64kx1, 64kx4, etc.

I would be grateful if someone could point me to a resource or shop for the chips I need for the modification. Thank you!

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By roadfighter

Champion (388)

Аватар пользователя roadfighter

17-04-2016, 09:11

I would recommend ebay or utsource.net
And the 41464 chip is a 4x64k chip. You need to piggy bag the chips you need the 18 pin chip.
Link to utsource.net: 41464 chip
You need 2 of them.

Cheers,

Emil

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

17-04-2016, 10:54

roadfighter wrote:

I would recommend ebay or utsource.net

Search either for "4464 DRAM" (without the quotes) and limit yourself to the 18 pin DIP packages. To be sure, I suggest that once you've made a choice, you locate a datasheet for that exact manufacturer+type, and verify pinout etc in there.

There are a few DRAMs out there that have "4" and "64" in their type, but confusing as to whether they're 64kbit (64k*1) or 64k*4. The # of pins tells you that: 64k*1 has 16 pins, 64k*4 has 18 pins.

Most of these IC's have 100 or 120 ns. access time. Some 80 or even 70 ns. ALL of that is fine. Smile

By lightman

Supporter (6)

Аватар пользователя lightman

21-04-2016, 17:37

Thanks for the replies, guys.

I think I've found the correct DRAM chips on an old PC gfx card, they are 41464 with 18pins and have 100ns access time according to the data sheet. Will give it a try with them.

Sadly, there seems to be an issue with the keyboard of my 8220 now, both shift keys stopped working all of a sudden. Any tips what the problem could be here?

Is there a way to enter quotation marks ( " ) and colons ( : ) with CHR/keyboard command without using the SHIFT keys? If so, I could at least continue playing H.E.R.O., one of my fave MSX games... Smile

Thanks again,

Boris

By Wild_Penguin

Hero (542)

Аватар пользователя Wild_Penguin

21-04-2016, 19:07

What is it with these shift keys????

Not that I'd have the same problem, but guys at this thread do!

EDIT3: Removed my CHR$ suggestion, which I put here originally since I didn't read properly

By kanima

Master (192)

Аватар пользователя kanima

22-04-2016, 02:43

lightman wrote:

Is there a way to enter quotation marks ( " ) and colons ( : ) with CHR/keyboard command without using the SHIFT keys? If so, I could at least continue playing H.E.R.O., one of my fave MSX games... Smile

Use the vpoke command to put " (34) and : (58) on the screen.
For example:

screen 0
width 40
cls
vpoke 3,34
vpoke 5,58

This will put a " and : on location 3 and 5 of the screen. Now you can move your cursor to the top-left of the screen and type run before the " and then a between the " and : and then hero.bas after the : to end up with

run"a:hero.bas

You might have to adjust the vpoke addresses depending on whether you're using run or bload and also if you're using another width than width 40 or if you're using screen 1 instead of 0 (in screen 1 the top-left is at 6144).

By lightman

Supporter (6)

Аватар пользователя lightman

22-04-2016, 19:08

Thanks a bunch, kanima, you just saved my weekend! Smile

Tomorrow I will have a look at the dead shift key problem together with a friend of mine who is more tech-savvy than myself. I'll report the result here, hope we will be able to fix it. If so, we will also add the extra DRAM chips that I've unsoldered from the gfx card.

By lightman

Supporter (6)

Аватар пользователя lightman

30-04-2016, 13:33

It's been a few busy days since I've last posted... but we made it! Smile

First we decided to upgrade the RAM to 128k. The DRAM chips I've unsoldered from the gfx card had very short pins so the upgrade was quite fiddly since also the space between the two original chips is very small and the distance between the pins and pcb is only about 1 or 2 millimeters, it was quite difficult to get them soldered in piggyback-style.

Here are some pictures:


Before the upgrade... (behold the big fat Z80 :) )


...and after. All pins except for pins 16 of the DRAM chips got soldered piggy-back to the existing ones, pins 16 got connected to eachother and soldered to point TP9 of the controller chip.


Finally, jumper JP2 got opened and JP3 closed to make the 8220 report its new RAM size on boot...


...and it does, hooray!! :D

If you want to do the upgrade as well but can't find proper DRAM chips, you can order them here as well: http://store.retroleum.co.uk/zx-spectrum-chips . It's a retro shop for Commodore and ZX SPectrum computers but the 41464 18-pin DRAM chips (second entry in the list) of course also work for the 8220 (and others). I've ordered some other stuff from them a while ago. Friendly service and fast shipping.

Now I hope that I will be able to load and play some of the bigger MSX2 games via tape interface.

Even better, we also fixed (well, hopefully) the SHIFT key issue. The keyboard of the 8220 is composed of a key layer with small springs and two conductive foil/plastic layers with carbon contact lines between them. When a key is pressed, the upper foil gets pressed on the lower one and closes the circuit. This is how it looks like:


Here we see the backside of the keyboard layer with all those small springs. Be careful when lifting up the keybed, it's best to turn it around first and then try to lift the contact foil layer, if you do it the other way around, the springs may fall out and it's quite a pain in the a... to put them back again (this happened to us, so...).


Looks like a public transport grid, eh? :) In this picture, the foil contact layers are shown upside-down, the SHIFT keys are on the upper left and right sides.

We took numerous measurements but couldn't find a dead spot/trace so we gently cleaned the space between the foils with pressurized air from the can and used one of those small electronics repair vaccuum cleaner things to get the dust out that had accumulated there. Now the SHIFT keys are working like a charm again!

If anyone of you needs high-res versions of the pictures above (and a couple more), feel free to contact me and I'll gladly send them to you!

I want to thank all you guys and Bas from bas-ditta.org for getting me on the right track!

From Germany with love,

Boris

By raymond

Champion (381)

Аватар пользователя raymond

30-04-2016, 13:24

Another NMS8220 with some extra memory Smile