30 Apr
2009
30 Apr
'09
7:36 p.m.
--- On Thu, 4/30/09, Ethan Dicks <ethan.dicks at gmail.com> wrote:
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).
Yeah, and 4164's are pretty easy to come by. I don't worry about modifying the
individual chips - but then again, I'm typically only using modified chips to replace
individual failed 4116's.
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.
Sounds like it would work perfectly. The only issue I would have with it is that the two
machine pin sockets you would need cost more than the 4164's do, and you have to
purchase those sockets new - whereas you can scavenge 4164's from junked XT clone
boards. :)
Good to know, but I have so many 4164s that I'm
unlikely to use 41256s.
Yeah, and 41256's are much harder to get - I just brought it up as a just-in-case. I
once spent an afternoon using a propane torch to scavenge soldered-in 41256's from
scrap HP printer boards in an attempt to upgrade a Sun VME machine.
In many instances, it's actually easier to modify the board to take 4164's than it
is to modify the chips or build adapters. But, again, that's not very original, and
involves hacking the board. I typically only use these one at a time when necessary to
replace bad chips (because I don't have any spare 4116's). I know a common
modification on Wiliams arcade games like Defender or Robotron (which use piles of
4116's) is to simply replace all the chips with 4164's and modify the board (two
trace cuts and one kludge wire) to take them. Or, in the case of the game, since nothing
else on the board uses 12v or -5v, you can actually build an adapter for the power
connector that disconnects the -5v, and routes the +5v to the +12v line - and then just
plug 4164's straight in with no modification.
It really depends on your application, and how the board you're installing them in is
set up. Do whatever works best for you and the particular machine you are repairing. But
you can definitely, replace 4116's with 4164's with minor modifcations and expect
it to work just fine.
-Ian