[Coco] 64 K upgrade for COCO 1 gives ?OM ERROR

[Bruce W. Calkins]

"E" and earlier boards needed some added wiring to a previously unused 
gate on a 74LS02 to properly switch the RAM.  Only the "285"/"F" boards 
were a direct upgrade.

OTOH; late CoCo 1with a non-chicklet keyboard should be a "285"/"F" board.

The high low jumper was for selecting the upper or lower bank of 
"half-good" 64k chips.

It begins to sound like a bad RAM chip, or perhaps a bad jumper or some 
other "little" detail.

This book link might help; <www.roust-it.dk/coco/littlewonder.pdf> 
Starting with page 82.

It does state that the jumper on the "285"/"F" boards were labeled 16/64 K

Bruce W.


On 5/2/20 6:00 PM, John E. Malmberg wrote:
> I have a COCO 1 later grey case with the non-chicklet keyboard.
>
> It was has a 16K memory badge.
>
> While the computer had 16 K memory in it, I was able to verify that it 
> had BASIC 1.1 ROM in addition to the ECB ROM.
>
> I tried to put 64 K using 2164 memory chips.
>
> The circuit board had 4 jumpers to move to go from 16 K to 32 K, which 
> I moved to the correct locations.
>
> The circuit board has a jumper set labeled high / low.
>
> The computer boots, displays the sign-on for Extended Color Basic 1.0.
>
> It reports ?OM ERROR for any command given.
>
> Any ideas?
>
> Regards,
> -John
>
>
>
>
>