[Coco] CoCo 2 64K upgrade blues

[Mathew Boytim]

Did you pull the pins 1 out of the socket before grounding?  If not I suspect the problem isn't the grounding of pin 1 but the shorting of whatever signal is on pin 1 of the sockets to ground.

Matt

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On Fri, 8/4/17, Carlos Camacho <idevgames at gmail.com> wrote:

 Subject: [Coco] CoCo 2 64K upgrade blues
 To: coco at maltedmedia.com
 Date: Friday, August 4, 2017, 9:34 PM
 
 I have a CoCo 2 with 16KB RAM. I decided to
 upgrade it to 64KB.
 
 Since I have a bunch of P21256-12
 chips, I decided to go with them.
 
 This CoCo is a 26-3026 using 8709416
 motherboard.
 
 My first step was to solder a wire
 between the two pads labeled W1.
 
 Looking at the 21256 datasheet, Pin 1
 is A8 and Pin 16 is VSS.
 
 When I switched the machine on, it
 booted fine. A PRINT MEM showed it now
 was a 64KB machine.
 
 It was recommended in the Facebook
 group that I ground Pin 1 to avoid
 memory issues as the machine is used.
 
 My first attempt, I connected each
 chip's Pin 1 to Pin 16. This didn't
 work.
 
 Next, I tried connecting all the Pin 1s
 together and go to ground on the
 motherboard. I tried to tap into the
 ground of the 6883 but it didn't boot.
 
 So, I tried to ground it on the RF box.
 It still didn't boot.
 
 The memory is fine because when I
 remove the grounding wire going to all
 Pin 1s, it boots fine.
 
 Summary: No wires on the RAM chips and
 machine boots fine. Try to follow
 advice to ground Pin 1 and machine
 doesn't boot.
 
 I'm really scratching my head on this
 one. Hate to have to buy 4164s when I
 have a bunch of the 21256s.
 
 Domo arigatou,
 
 Carlos Camacho
 
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