GX4000 Ram upgrade

[eto]

I have seen this PCB on Facebook and it seems to be a very simple RAM upgrade for the GX4000. I haven't found this documented anywhere, but it seems to be as simple as removing a RAM chip, adding this PCB with 2 RAM chips and you are all set. Is this really possible?

[gerald]

I've made similar board eons ago but for both RAMs (ie 2 chip to 4 chips).

The main issue is that there is not much space in the GX4000 case for such an assembly, be it on height point of view (the power switch) or on the side. The board I made required filing the PCB on the side to match the case, and final prevented the case to be close due to the power switch.

I finally find it easier and faster to piggy pack the ram and have a single wire for the CAS signal.

[eto]

I finally find it easier and faster to piggy pack the ram and have a single wire for the CAS signal.

Where would CAS1 come from? Is there a connection easily availably on the board?

[gerald]

CAS1 is the tricky part : you have to solder a wire on ASIC pin 91. It's not available anywhere else.

[AnakinTF]

You need to remove the original RAM chip and replace with that board. The new RAM must go without sockets to fit it in place. Like you see in the board you need make a connection in two points, 1 point in the first board to pin 91 on ASIC and second a connection between two boards with 2Board pin. Remember use capacitor and resistor.

[CraigsBar]

You need to remove the original RAM chip and replace with that board. The new RAM must go without sockets to fit it in place. Like you see in the board you need make a connection in two points, 1 point in the first board to pin 91 on ASIC and second a connection between two boards with 2Board pin. Remember use capacitor and resistor.

When fitted like this. Does the case close? 
if so where can I get some boards? I'd love to have a 128k GX4000 

[Richard_Lloyd]

@AnakinTF  Nice work!

Hi, are you prepared to share the Gerbers so that I can get some boards made? If not, may I create Gerbers from the photographs?

Cheers, Richard.

[TotO]

Peoples selling PCB... And deal with that. 

[CraigsBar]

You need to remove the original RAM chip and replace with that board. The new RAM must go without sockets to fit it in place. Like you see in the board you need make a connection in two points, 1 point in the first board to pin 91 on ASIC and second a connection between two boards with 2Board pin. Remember use capacitor and resistor.

When fitted like this. Does the case close?
if so where can I get some boards? I'd love to have a 128k GX4000

OK in the end I used the piggyback and 2 resistors technique. And I now have a perfecly working 128k GX4000 (or GX4128k perhaps) tested with Puzzle Bobble and CPC Diag carts. all work fine.

[eto]

Great! :-) 

Could you add that to the DIY section of the Wiki? I think this could be really valuable for others. 

https://www.cpcwiki.eu/index.php/DIY#ROM_.2F_RAM_Expansions

[AnakinTF]

@AnakinTF  Nice work!
Hi, are you prepared to share the Gerbers so that I can get some boards made? If not, may I create Gerbers from the photographs?
Cheers, Richard.

Of course you can create your own PCB

[AnakinTF]

PCB design was released on my github for a long time, but because of people becoming professional haters I've stopped sharing some stuff.

[Richard_Lloyd]

PCB design was released on my github for a long time, but because of people becoming professional haters I've stopped sharing some stuff.

Sorry to hear that - you do a lot for the Amstrad world - thank you.
I'll start on my own PCB.
Cheers, Richard.

[CraigsBar]

That's a 2nd one done with the piggyback method. Pin 91 is still a bitch to connect to! but all in all it is not too hard. Just making sure the 33ohm resistor lead is tinned before trying to attach it to Pin91. The 10k resistor over the top of IC8 (Pins 8 and 11) can be made really short and snug to the IC leaving only connecting the CAS signal from the new RAM IC's (Pin 16) to the other end of the 33ohm resistor and all other legs on the 2 new ram to the originals on the board and the piggyback mod is complete..

A quick test with Noel @llopis 's Amstrad Diag cart to check the Ram is all working and it's time for CRTC3

[eto]

Just making sure the 33ohm resistor lead is tinned before trying to attach it to Pin91.

Is that resistor required? The Wiki page doesn't mention it. 

https://www.cpcwiki.eu/index.php/128k_on_GX-4000