Gemini 1MB RAM expansion for Amstrad Plus

[PulkoMandy]

It seems the board was damaged after my testing or during shipping. You can send it back and I will send you another one.

[darkhalf]

Okay thanks. I'll have a look over the microscope tomorrow and see if I can find anything before going down that path

[GUNHED]

@PulkoMandy received my board today thanks, but it is showing as 512KB mode with the '2MB' switch set on my CPC464 plus. I will note there are some (but not all) extra banks showing up in Amstrad Diag (see pictures)

Also tested this on a CPC6128 using Symbos and showing 640KB (other memory test programs also showing 512KB)

Any ideas on this one?

You should test it with the tool 'OS Infos' under FutureOS. Because this will show you up to 4 MB of connected RAM. The latter software only shows you only up to 1 MB due to its limitations.

A video is here: 
https://youtu.be/h2RGjXUooiQ?t=30
At second 39 the full 4 MB of RAM are shown.
In your case it shall show 2 MB like it's expected.
Good luck!!! 

[darkhalf]

The latter software only shows you only up to 1 MB due to its limitations.

Thanks but I've got just the 1MB board, so Symbos/Diagnostics should be sufficient for testing this

It seems the board was damaged after my testing or during shipping

@PulkoMandy looks like there was some rework on the board received. The chip appears to have been removed and is missing a number of pads on the PCB. Also the rear switch has had tracks cut. The tracks where cut were shorted to the backplane, and the wires have come off and are melted.

Where is the yellow wire meant to go? I can try and get this going here before spending the $15 and waiting another month to swapping the board

Just some suggestions when removing / replacing chips. Use a product called Chip Quick to remove the solder easily. It is an alloy material which melts the solder at a lower temperature level. Otherwise use a narrow tip hot air gun/rework station to remove the chip. This should help avoid lifting pads. Afterwards use copper desoldering braid to clean the pads before replacing the chip. Any kind of rework with wires should use single core wire (multicore is too bulky for thin PCB tracks). Also the usage of flux will help the solder flow

[PulkoMandy]

Yes, I know all that

This is the first board I made and it took a few retries to get things right. Unfortunately this means unsoldering the GAL to reprogram it sor each change... so it suffered a bit from these experiments.

I think the yellow wire goes to the ground plane. Initially the board was designed for 2MB chips, but due to the chis shortage at the time, only 1MB chips were available. So, the unused address bit is grounded.

Your problem will likely be with the orange wire, which either lets another extra address bit go to the memory chip, or force it to ground. Or maybe you can trace it back on the other side of the switch up to the register which stores the current memory configuration

[darkhalf]

unsoldering the GAL to reprogram it sor each change

Yeah that is a bit of a pain with SMD stuff. Okay I did a reflow of the components on both sides of the board and used single strand wires and put in positions you mention and all good

Now shows 1MB and now the expanded memory plus games can be used 

[PulkoMandy]

Ok, it's nice that you could fix it by yourself

[Solo Kazuki]

Hi

Actually I'm interested in 2MB expansion, but if it's not possible then I'm interested in 1MB one.

[PulkoMandy]

I was a bit busy this week. Both versions are available, I'll reply to your PM later today.

[hsimpson]

Hi

I'm interested in 2MB expansion (plus version).

[hsimpson]

The parcel arrived safely. Thanks a lot PulkoMandy .

[dodogildo]

Pls someone show me how to have this on GX4000?

[PulkoMandy]

You would need to add an expansion port to your GX 4000.

Maybe something like this: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/gx-4000-to-6128-conversion-kit/ but I don't know where this adapter can be ordered (if still available)

[eto]

Is there any relevance for the GX4000? Without mass storage and keyboard there is little(no?) use for 1MB of RAM. Maybe some 128K games are nice but for that it's much easier to piggy-back 2 RAM ICs.

[PulkoMandy]

Even on a normal CPC I have no idea what people do with that much RAM 

But, more seriously, yes, it doesn't seem very useful on the GX4000 to me. When you can have 512K cartridges, the 64K of RAM are already quite a lot, in fact.

[McArti0]

Even on a normal CPC I have no idea what people do with that much RAM.

The catch is that people never use RAM. Only software uses RAM 

[HAL6128]

Even on a normal CPC I have no idea what people do with that much RAM 

SymbOS is able to use max. 1MB. It fits perfectly. Of course not on a GX, but runs well on a regular or plus model. So, cool device.

[dodogildo]

Is there any relevance for the GX4000? Without mass storage and keyboard there is little(no?) use for 1MB of RAM. Maybe some 128K games are nice but for that it's much easier to piggy-back 2 RAM ICs.

You're right. My only intend is to be able to run 128K games on GX4000 of course... 

[eto]

You're right. My only intend is to be able to run 128K games on GX4000 of course... 

I've upgraded two GX4000 to 128K already. The only delicate part is to properly solder a thin wire to one of the ASIC pins. The rest is quite straight forward. 

In general it would be much less effort and less risk to piggy back the RAM than modding the GX4000 to support the GeminiRAM expansion. 

[GUNHED]

Even on a normal CPC I have no idea what people do with that much RAM 

But, more seriously, yes, it doesn't seem very useful on the GX4000 to me. When you can have 512K cartridges, the 64K of RAM are already quite a lot, in fact.

Well, I use the 2 MB version with pleasure and I'm happy to have 2 MB and not only 1 MB.