22 May
1997
22 May
'97
11:05 a.m.
> I have found what seems to be a decent supply of eproms. I was looking at
> an old 2400 baud fax modem for my pc, and noticed that it had what looked
> like an eprom on it. I pulled the chip and peeled off the label, and it was
> a 27256 eprom. I also bought a 2400 baud modem at a thrift store for $2.00
> and it had a 27128 eprom in it. This was cheaper than buying the eprom by
> itself. I paid $3.00 for a 2764, and didn't even price a 27128. I am going
> to start picking up all of the old cheap, almost worthless modems and
> grabbing the eproms out of them. You can probably pick up the modem for
> less than the price of the eprom that it holds. If anyone else knows of a
> cheap source of eproms or other chips, share it with us.
Others have said that you should be careful that what you strip for parts
is not some piece of computer history. I guess you're pretty safe with
'generic' PC clone bits (although I personally preserve true-blue IBM
hardware...), but anything else should probably be kept as-is if you're
not sure about it.
On the other hand, I got some old PCBs that had had the gold connectors
cut off (for 'recycling' :-(), and I intend to at least remove the
socketed IC's from those. They're mostly common 68000 stuff + ethernet +
SCSI+ etc, but they are worth saving, and the boards are useless as-is.
Hamfests are the best place to pick up spare chips. Many vendors are
simply regular guys just trying to clean out their basements, others are
psuedo-commercial vendors. Of course, it is just a big crap shoot - some
fests have yeilded only boards with standard TTL/CMOS, other fests have
yeilded more exotic species ($2000 1M Rad-Hard EEPROMS (buck a tube!),
GaAs glue logic, early weird 68000 variants, etc.). Of course, the
chances of finding exactly what you need on the first try is, by Murphy's
Law, slim (it does, however, justify going to every hamfest possible!).
I'm always a little careful about buying chips at radio rallies
(hamfests). They're the one thing I can't fix if they are defective, so I
don't pay that much for them. On the other hand, I do buy up 2900-series
chips whenever I see them - they are sufficiently rare to be worth
grabbing.
Unlike valves (tubes), where a quick test with an Ohmmeter will tell you
if the heater is burnt out, there's no quick test for finding really dud
IC's AFAIK. Maybe I should design a pocket IC tester....
I must caution that we must be careful what we scrap - for example, I am
pretty sure I scrapped out a bunch of CA Naked Mini (sound familiar?)
Argh!!!
I think we should use this list when we need parts.
Some of us
probably have mountains of chips (at least I do). If you need a specific
Indeed. Most serious computer collectors keep all sorts of spares in their
junk box. Would you believe a spare ASR33 motor (50Hz model), head stacks
for a TU16, head assemblies for Northstar disk drives, DEC flip-chip
cards, Anadex printheads, etc, etc, etc.
chip, post something to the list - perhaps one of us
has a tube of the
things we never knew we needed. I do not think anyone here is out to make
money on such small deals.
Another thing: If you get a computer from a company, university, or
similar (as opposed to a private individual), ask if they have any spares
around. Sometimes all sorts of things turn up. I was once offered (along
with some other people) a PDP11/34 CPU. Now, they're quite common, but
also quite nice, and I grabbed one. I then asked if there were any spares
available. I was then offered an assortment of DEC comms cards (DMC11's,
DMR11's, KMC11's, DJ11's, etc), cables, boards, test boards, extenders,
RK05 heads, alignment disks, alignment tapes, PSUs, switches,
brand-new-in-bags DEC components, etc. That's just one example - it's
happened several times, and you lose nothing by asking.
Regarding EPROMS and PALs: I would stock up on them, as both are becoming
obsolete. Flash technology has nearly wiped out EPROM demand, just as GALs
and FPGAs are pushing out PALs. And if you see ANY early or wierd EPROMs,
Well, yes, but I don't insist that all my machines have all-original
components. If a PAL failed in my PERQ, I'd replace it with a GAL, no
question. The machine would work again that way. Of course, if I then saw
a suitable blank PAL I'd probably swap it in, but I'd not class it as
urgent.
Similarly, apart from the _strange_ 1702, it's often very easy to use
larger modern EPROMs in place of older ones. Or you could use EEPROMs
(Microchip et al make at least the 2K * 8 (2816) and 8K*8 (2864) ones) -
the pinout is almost the same as the 2716 and 2764.
If you are a purist, this probably won't help you, but I've used tricks
like that to get old machines running again. I wonder how many people have
noticed that if you take a 4164 64K DRAM chip (commonly available on old
PC memory cards), bend up pins 1 and 8 (N/C and +5V), and solder a jumper
from pin 8 to pin 9 (A7), the result will work in a
4116 socket (although
using only a quarter of the chip). I used that to get a very
dead Tekky
graphics terminal running again when I couldn't get a 4116 in a hurry.
namely 1702s and 2532s, GET THEM. Today they are quite
rare, tommorrow
Don't forget the 2708 and the 3-rail 2716 (Texas Instruments).
Also, how many people have programmers that can handle these? I have the
original Intel programmer (part of the MCS8i) for the 1702, and a little
thing that covers everything from the 2704 (! - it's a half-size 2708) to
the 2732 for the other classics. The latter needs repairing, but it should
be doable.
Most modern programmers _cannot_ handle 3-rail EPROMs, and the
manufacturers think you're mad for asking.
they will be gone.
William Donzelli
william(a)ans.net
--
-tony
ard12(a)eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill