Modding the 3K RAM or Super Expander cartridge

Mike · Post by **Mike** » Tue Mar 10, 2009 4:42 am

After seeing the PCB of the VIC-1211A Super Expander in the Denial Wiki it occured to me, that one could install an additional RAM chip with at least 8K.

Since I do own a 3K RAM expander, which IIRC uses the same PCB, I'd like to do the following mod:

- Soldering a 2732 EPROM in the upper place, with Hypra System (a floppy speeder),
- Soldering an 8K or 16K RAM chip in the other place, which should appear in BLK1 (and BLK2),
- modifing the PCB to get both chips working.

I'd produce a special version of Hypra System which places the transfer buffer into the area of $0400 .. $04FF. There will be no harm for BASIC, as the 3K gets deactivated anyway by the 8K or 16K RAM. It's still possible to revert to the standard 3K RAM expansion with POKE642,4:POKE644,30:POKE648,30:SYS64818, thereby deactivating Hypra System.

Has someone here done a similar mod?

Greetings,

Michael

Update: I found this article on Zimmers: Page 1, Page 2, and Page 3. It however states using the 2732 causes "problems", and it doesn't mention populating the sockets with RAM. Well, I'm not afraid cutting traces, and re-wiring the PCB.

Update 2: In case you're wondering what became of this project, look here: VIC-2020 MINIMON.

6502dude · Post by **6502dude** » Tue Mar 10, 2009 8:30 am

Sounds like some neat ideas.

You may need to reroute traces on PCB to replace the rom with a 2732 eprom, but this is not difficult.

The same would be the same case to install a 6264 ram chip in lower space + need to extend R/W line from edge card to the RAM chip.
I don't think there is a 16K ram chip in a 24 pin package. So, you are limited to 8K of RAM expansion.

Actually the 3K will not get deactivated with 8K RAM addition. It is simply that Basic does not use it for program storage. However you can still use it to store temp data, variables, etc.

Mike · Post by **Mike** » Sun Mar 15, 2009 8:37 am

I found time this weekend to open my 3K RAM expander, and made a two-side scan of the PCB:

Component side

Soldering side

6502dude wrote:You may need to reroute traces on PCB to replace the rom with a 2732 eprom, but this is not difficult.

The 2732 can be installed directly into the socket. To reroute the traces I came up with these 3 cuts, and 5 new wires:

* cut trace on component side between upper, and lower socket pin 18 (former address line CA11),
* open pad 12 lower, and
* open pad 11 upper,

* wire from pad 11 top left to pad 12 top right (connect CA11 to pin 21 of both sockets),

The same would be the same case to install a 6264 ram chip in lower space + need to extend R/W line from edge card to the RAM chip. I don't think there is a 16K ram chip in a 24 pin package. So, you are limited to 8K of RAM expansion.

As the 6264 also is a 28 pin package, it needs to be fitted with its lower 24 pins into the lower socket, with its pins 1, 2, and 27 bent straight before. Pin 28 (Vcc) should fit into the soldering hole of the capacitor. Then:

* wire from pin 18 to pin 20 on upper socket (connect /CS and /OE),
* wire from pin 18 to pin 20 on lower socket (connect /CS and /OE),
* wire from pin 27 of 6264 to VR/W via (connect /WE),
* wire from pin 2 of 6264 to pad 12 lower left (connect CA12).

Not tested out ATM! This will need to wait at least until next Friday. I'll then post the results.

Actually the 3K will not get deactivated with 8K RAM addition. [...]

Yep. BASIC just wants continuous RAM.

Greetings,

Michael

rhurst · Post by **rhurst** » Sun Mar 15, 2009 11:33 am

Very encouraging ... if successful, I'd like to follow this mod too -- I have a VIC-1210 3K RAM PACK that could use an upgrade like this.

ral-clan · Post by **ral-clan** » Sun Mar 15, 2009 5:22 pm

Hey Mike! Can I put your scans on the 3K RAM Wiki page? Your scans are better than what's there currently.

Mike · Post by **Mike** » Mon Mar 16, 2009 2:14 am

I had already put these two on the Wiki page of the 3K RAM expander + some new text.

The PCB shown on the Super expander page additionally features the 2532 EPROM (+capacitor).

Greetings,

Michael

ral-clan · Post by **ral-clan** » Mon Mar 16, 2009 7:15 am

Thanks. It's great that people with technical knowledge, like yourself, are making contributions to the Wiki.

Clockmeister · Post by **Clockmeister** » Sat May 02, 2009 8:54 am

I just modded a super expander to RAM cart by adding a couple of 8K 6264 (actually compatible cache RAM salvaged from an old PC motherboard) SRAMS to the 24 pin ROM sockets (with suitable adaption from 24 pin 2364 - to 28 pin 6264 (like 2764) but the /we pins need to be connected to /we at the cartridge connector. Then it was just a question of cutting the block select jumper pads and adding a dual throw two position switch (or three position for disabling the RAM) to select between blocks 3/5 and 1/2.

Position 1 is for the cart emulation and position 2 adds 16k to basic.

There is no reason why an EPROM can't be used in one socket. I used a 2764 myself and adapted it to the top 2364 socket and jumpered it to use block 5.

English Invader · Post by **English Invader** » Sat May 02, 2009 1:02 pm

I've only just started learning VIC BASIC, but I saw some software on Zimmers that disables expansion memory. I don't know if that would be of any use to you or not.