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CoCo 1 Rev D Board: Upgrading from 16K to 64K

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OK, now that I got my original CoCo fitted with the HJL 57 keyboard, on the next project...

I have downloaded the May 1984 issue of Rainbow (p 49) that details how to do the memory upgrade from 16K to 64K on my CoCo 1 Rev D. Not the easiest procedure of all the CoCos, but nothing I don't think very difficult either.

https://archive.org/details/rainbowmagazine-1984-05

A couple of quick questions before I get started:

1/ Is it OK to mix 120 ns and 150 ns chips?
2/ Are all 4164 64K? (I have several different manufacturers)
3/ When wiring to an empty DIP socket (the result of bending the respective pin up), what is the best/cleanest method to do so? Insert wire into socket? Solder wire to socket (but heat will damage socket plastic).
4/ Any other concerns/tips about the upgrade procedure?

Thanks!

Cary
 
Hi Cary,

1. It's not ideal but it does work most of the time on such slow old computers.
2. All 4164s are 64K but you need to make sure you find chips with the 128 cycle refresh (which is most of them)
3. Trial and error. Sure it's not better to just solder a wire the to the underside of the the socket?
4. Check your Color Basic version, it needs to be 1.1 or 1.2, if it's 1.0 then the 64K upgrade won't work.

Also I use the instructions from Hot Coco mag June 1985 page 54-55 if that helps.

Ian.
 
Thanks as always for the guidance Ian.

Regarding #3, it really has me perplexed. Underneath would be the easiest route but the problem would be running the wires back to the top. Also, the RF shield covers the area creating further logistical issues with wire routing. I have looked everywhere for a mboard picture of a converted 64K D board but no luck.

RE #4, it has EXTENDED color basic 1.0 - I believe that should permit 64K???

Will check out the Hot CoCo mod...
Thanks again!
 
Oh, ok...thanks Ian. The computer is unfortunately disassembled. Will try to get a later ROM just in case. Will a CoCo 2 ROM work? I have a CB 1.3.
 
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OK guys..just a quick update following completion of the upgrade. This was a tedious operation, but here's what I did in case anyone may want to do the same.

There are a couple of ways to upgrade an original CoCo 1 (D Board) to 64K. After a bit of research I elected to use the May 1984 Rainbow procedure (link in my original post). I am no expert in hardware, so the greatest challenge for me was the wiring logistics. In particular, wiring from a lifted chip pin to a socket. After considering various ways in which to do this, and thanks to insight of the members, I elected to run a wire bundle from pin 9 of each ram chip from the underside of the board. The top area of the board which houses the RAM is covered by shielding, so I ran the bundle from underneath through a small opening near the keyboard connector. From there, it was simply a matter of running each wire to pins 1 and 8 of each ram chip. I was a bit concerned about the length of the thin wire (longest about 12") carrying 5V, but found the voltages after the mod to be rock solid at each chip.

Ian correctly noted that 64K requires Color Basic 1.1 or higher (regardless of Extended Color Basic version). Mine had 1.0 (EXEC 41175 will give you the ROM ID). I replaced the Color Basic ROM with v1.2 (for early CoCos with dual 24 pin ROMs, the Color Basic is in the lower numbered socket while Extended Basic is in the higher numbered socket).

IMG_1042.jpg

A few additional wires per the instructions and voila:

IMG_1037.jpg

The RF shield fits just as did prior to the mod (note the wire bundle coming from the underside of the board to the right of the keyboard connector)

IMG_1041.jpg

Add a 64K RAM badge and done!

IMG_1039.jpg

I ran a bunch of tests and everything checks out perfect. PRINT MEM will not give you proof of 64K as the upper 32K is reserved. 64K and 32K machines will return the same mem value, about 22K.

So I found a clever little program that helps to verify the amount of memory in a 64K CoCo. In a nutshell, it copies ROM to RAM (the upper 32K) and makes a POKE change to verify the ROM changed and in doing so, verifies that the computer has 64K. If the computer crashes and/or the change is not noted (changes the prompt from OK to OY), then 64K is not available.

IMG_1040.jpg

The details of the ROM to RAM program are here:

https://subethasoftware.com/2016/01/19/64k-trs-80-coco-memory-test/

As a final test, I ran a CocoChek RAM test and booted OS9 which requires 64K.

DSC_6760.jpgDSC_6761.jpg

Thanks to everyone for your input.

Cary
 
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Great job! I have a question for you, where did you found the 64k badge ? I search this badge and found nothing. Thank you
 
This is why I was such a fan of the revison F board. Just swap the socketed chips and clip out the terminating resistors.

1670746092209.png
Though yeah, getting a proper ROM is a pain. For some reason my F board Coco (that came in a stack of "dead" machines) had colour basic 1.0 so when I did the upgrade it didn't run right. Pulled a 1.3 from another machine and off to the races.

That "box of coco's" I got ended up all sorts of fun. Like the dead beyond repair 2 (looks like the traces went up in fire?!?) I ended up pairing the full size keyboard with this F board in a B case. Was annoyed the A (black plastic) case was cracked in two, as they look amazing bead-blasted to bare plastic.

I've actually got a bunch of rev D's (complete machines) that are piggy-backed to 32k I should unload to make room.
 
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