30 Apr
2009
30 Apr
'09
7:15 p.m.
On Thu, Apr 30, 2009 at 2:57 PM, Mr Ian Primus <ian_primus at yahoo.com> wrote:
--- On Thu, 4/30/09, Ethan Dicks <ethan.dicks at gmail.com> wrote:
Ah... that makes perfect sense.
Is this hack as simple as
eliminating the -5V and +12V to the socket...?
Yup. That's _nearly_ all there is to it. You need to change the +12v into +5v...
and disconnect the -5v entirely.
Sure.
You can modify a single chip by bending pin 8 up and
folding it over and soldering it to pin 9 (may need a bit of wire), and clipping off pin 1
completely.
Hmm... I have so many 4164s that I'm not horrified to mod the chip,
and I might have to do that if there isn't enough vertical clearance
(not an issue in a PET, but might be an issue in the TRS-80 Model
III).
As for a socket mod, how does this sound? ...
Take a 16-pin machined-pin socket. Poke out pin 1 (-5V). Poke out
pin 8 (+12V). Take another 16-pin machined-pin socket. Remove pin 1
on it as well. Break off the pin tail from pin 8 so that it won't
dangle into the socket below. Install a jumper wire from the modified
pin 8 to pin 9 (+5V). Install that socket on top of the previously
modified socket (the one with pins 1 and 8 missing). Insert a 4164
into the top socket. Install the stack into a 4116 socket on the
target board. Repeat 7 times for a bank of 8.
I think I can find the used 4164s I removed from my DEC Professional
350 when I upgraded it to two banks of 41256s. I think that would be
a suitable source of parts to upgrade a PET - a donation from another
classic machine.
You can also modify the board. If you tie pin 1 of the
sockets either high or low, you can also use 41256's.
Good to know, but I have so many 4164s that I'm unlikely to use 41256s.
-ethan