10866 24JUL86-0818 Product Reviews & Announcement
RE: EPROM PROGRAMMERS (Re: Msg 10810)
From: MARTYGOODMAN To: GOBLIN
You clipped the right caps, and apparantly have successfully
moved the jumpers and replaced chips and added the jumper
for the MA7 line so as to get a 32K computer.
(note… it is preferable to use a ferrite bead, rather than
a 33 ohm resistor… but this is a minor point)
Now, to upgrade to 64K, you need to do a bit more stuff:
REMOVE the 74LS02 chip (U29 on the E board).
Bend up pins 4,5,and 6 on it. Also, remove the 74LS138 chip
(U11 on the E baord). Bend up pin no. 5 on it.
Now wire pin 4 of the 74LS02 to pin 5 of the 74LS138 (using long
enough wire so that when you plug the chiops back in their
sockets the wire will reach).
Run a short jumper wire from pin 6 of the 74LS02 to pin 8
of the 74LS02. Note that pin 8 of the 74LS02 will still
be pointing down and should still fit into the socket
when you plug the 74LS02 back in! So be careful
when you solder the wire to pin 8… make sure
to hook it near teh top of pin 8 and use minimum
amt of solder! Finally, run a longish wire from pin 5 of the
74LS02 all the way over to connect it to TEST POINT ONE on the
E board. This is an upright staking pin located near the 6809 chip,
lying between it and the 40 pin connector for the disk controller.
Plug the 74LS02 back in , and do likewise for the 74LS138.
Be sure the HixDgh / Low jumper is set to LOW.
You should now have a 64K (acutally 96K) CoCo.
Use CMEMTEST in the util section to check it out…
that is the best memory tester for the current coco ever written.
After you are sure all is well, I URGE you to REMOVE all the jumpers
one by one, and instead of jumpering the pins in question, SOLDER them.
For you will NEVER want to downgrade to 16K!!! And a solder connection
is more reliable than those jumpers… there have been cases of flakey
CoCo’s made flakey due to oxidation of teh jumper contacts.
Hope this solves yer problems!
Lemme know how it goes.