[Coco] CoCo1 Rev E 64K Upgrade by Kitsz

[Darren A]

I have a Rev E board which has been modified for 64K (not by me).  I
sent the OP a digram which illustrates the modifications that were
made to the board. It matches the instructions you supplied from the
CCM article except that it uses pins 1, 2 and 3 of U29 instead of 4, 5
and 6.  I suppose you could use either set of pins since both of those
NOR gates (A and B) in the chip are otherwise unused. Also, instead of
connecting one of the jumper wires to TP1, mine connects it to pin 21
of PIA U8.  That's the same signal (R/W), so I assume it was chosen
for its proximity to U29.

The instructions you listed don't mention anything about R83.  Perhaps
that is in Step 6 which appears to be missing. I've seen two other
documents say that a 33 ohm resistor needs to be soldered to those
pins. My board has a jumper between those two pins rather than a
resistor. Does anyone know if that could cause a problem?

Darren

--------------

On 9/14/08, theother_bob wrote:
> For the sake of a quick reply I am typing in the relevant portion of the
> article so you don't have to wait for me to set up my manual scanner. This
> is from The Color Computer Magazine, Oct. 1983, Custom Color by Dennis
> Kitsz, pp31-48 (wow! a mini-mag in itself, covering the lowerkit, 64k
> upgrades for all models up to NC board and installing aftermarket keyboards
> in the CoCo.)
> -----------------------------
>    64K Upgrade, Radio Shack style--Rev.E. Needed: screwdriver to open the
> case, snips, solder and iron, thin wire, eight 64K RAMs (type 4164/4864).
>
>    1. Unplug and open the computer
>    2. Remove the RF interference shield by cutting the white plastic straps
> and working the cover around the edges.
>    3. Move four jumpers (one between U4 and U8, and three above the keyboard
> connector) up and over to the 32K position.
>    4. Move the remaining umper (below C44) up and over to the 16/32K
> position.
>    5. Solder or jumper together the two LO staking pins next to U29.
>    7. Carefully remove U29 from its socket, and bend pins 4, 5 and 6 up and
> parallel to its body.
>    8. Remove U11 from its socket, and bend pin 5 up and parallel to its
> body.
>    9. Replace U29 and U11 in their sockets, except for the pins noted.
>    10. Connect three wires: from U29 pin 6 to U29 pin 8; from U29 pin 4 to
> U11 pin 5; from U29 pin 5 to TP1.
>    11. Clip out capacitors C61, C31, C64, C35, C67, C45, C70 and C48.
>    12. Remove the eight 4K or 16K memory chips U20 through U27.
>    13. Install eight 64K memory chips, pointing in the same direction.
>    14. Restore the interference shield and press it down, replace the cover,
> and power up.
>    15. PRINT MEM should reveal a 32K machine.
>