30 Apr
2009
30 Apr
'09
10:40 a.m.
On Thu, Apr 30, 2009 at 6:33 AM, Mr Ian Primus <ian_primus at yahoo.com> wrote:
4116's need -5v from the power supply.
And that -5V has to come on first and go off last. I was recently
reading the Circuit Cellar volumes where this subject came up -
powering down last is easy - there's little load, so the filter caps
discharge last in the PSU. Coming up first takes some intentional
design choices in the PSU, but from what Steve Ciarcia describes, it's
not a difficult thing to get right. Any existing 1970s microcomputer
is already going to have that problem solved.
They also run very hot. They're pretty unreliable,
and a common source of problems in machines.
I don't remember having a single problem with 4116s in Apple IIs or
PETs back in the day, but I will grant that the 4116 is probably going
to be less reliable than the TTL in those same machines.
Not to say they're terrible - they are good for
what they are... but they are nowhere near as reliable as 4164's
Agreed.
Note that with a little modification, you can make
4164's work in the place of 4116's. They have almost the same pinout, they
don't use -5v, and they run much cooler.
I was thinking about that very subject just this week - I have a
TRS-80 Model III that I think has a flaky 4116. I have a chip tester,
but it only tests 64Kbit, 256Kbit and 1Mbit DIP DRAMs (i.e. -
single-supply parts). Is this hack as simple as eliminating the -5V
and +12V to the socket, or is there more to it? I have tubes and
tubes of NOS 4164s, and could easily build a 1-2-socket stacker with
missing pins to plug a 4164 into a 4116 socket if that's all it takes.
I also have a PET 4016 with the punched-out holes in the upper 16K
region of the board - I don't mind stringing wires to rebuild the
sockets, but that seems like a great candidate for hacking the power
to the RAM field. Also, it would be easier to drive a naked dynamic
PET board from a bench supply if it didn't need -5V.
So for multiple projects, I'm intereste
-ethan