[Coco] Upgrading RAM for CoCo 1

[Barry Nelson]

This is what I found.

http://sparksandflames.com/files/TandysLittleWonder-2nded.pdf

"E" boards were the first to be upgradable to 32K. These require simply installing 64K chips in place of the existing 16K units and moving the jumpers (one between U8 and U9, three next to the keyboard connector, and one just below C44) to the 32K position. Hmmm... 64K chips but only 32K RAM? That’s correct! 32K was selected as the maximum supported RAM because Color BASIC couldn’t use more than 32K anyway, and no other operating system was available at the time. There never were any 32K DRAM chips made. 32K chips were made up by piggy backing 16K DRAMs, even commercially! Tandy got discount prices on half good 64K chips (half bad?). There is a jumper located near U29 marked HIGH and LOW. This selected either the upper 32K or lower 32K halves of the 64K chips (all the chips had to have the same half bad, Tandy just sorted them before installing). If new chips were purchased, it won’t matter which half is selected. Later versions have all good 64K DRAM as the supply of half-good chips dwindled.

On page 69 of this pdf, it shows the 16k/32k jumpers, one of which changes a line going to the ram chips from 12v to 5v.

http://sparksandflames.com/files/Color%20Computer%20Technical%20Reference%20Manual%20(Tandy).pdf

On Apr 24, 2015, at 11:05 PM, Don Akins <donald at dra.space> wrote:

> Will those 5 volt chips work in the CoCo1 or do I need to do some modification to make them work?
> 
>> On April 24, 2015 at 10:45 PM Barry Nelson <barry.nelson at amobiledevice.com> wrote:
>> 
>> http://www.jameco.com/1/1/1851-4164-150-dram-64k-x-1-120ns-dip-16-memory.html
>> 
>> On Apr 24, 2015, at 10:19 PM, coco-request at maltedmedia.com wrote:
>>> Date: Fri, 24 Apr 2015 22:19:46 -0400 (EDT)
>>> From: "donald at dra.space donald at dra.space" <donald at dra.space>
>>> To: coco at maltedmedia.com
>>> Subject: [Coco] Upgrading RAM for CoCo 1
>>> Message-ID:
>>> <1025448239.115410.1429928386457.JavaMail.open-xchange at app4.ox.privateemail.com>
>>> 
>>> Content-Type: text/plain; charset=UTF-8
>>> 
>>> Hi Guys,
>>> 
>>> 
>>> I recently bought a silver CoCo 1 and when I booted it up it only recognized 8k
>>> ram out of 16k. So I opened it up and noticed that some of the ram chips
>>> appeared to have burnt out. The motherboard has jumpers for 64k so this board
>>> must be one of the later revisions of the CoCo 1. I pulled one of the chips I
>>> out which is a 4116N-3GP. Are there any equivalent 64k chips out there today for
>>> a CoCo 1?
>>> 
>>> 
>>> Don
>> 
> 
>  
>