On Wed, Dec 13, 2017 at 9:08 AM, Mark G Thomas
via cctalk <
cctalk at classiccmp.org> wrote:
I am working on several projects requiring 2708 and 2716 EPROMs, and
am finding some of my chips will not erase, and some will not take
a program. I've also learned more in the past week than I wanted
to know about repairing Data-I/O 29a/b programmers.
I vaguely remember in the 1990s baking such EPROMs in the oven, but
I do not remember temperature or time. I was surprised that Google
didn't turn up anything useful with this info.
I'm sure someone here will have some notes on EPROM baking.
If this is an issue about reviving bad eproms? I assume you have tried
What process are you using now to erase 2708/16's? I have a simple
unit and it seems to always work. Some eproms go bad but I never have
issues with erasing them. My point is that maybe you need a better prom
They seem to erase fine, using a PRO-LOG 9103 eraser (box, timer, tube...)
I would avoid baking them until you have
options. Not sure what others think. This topic has come up before
about putting them outside and all that. The erasers are all over ebay,
and the hardware store is full of the correct types of lighting, why not
make a box that will do the job? I assume there is more to it that
simply erasing them.
Erasing seems to work fine. It's the re-programming them that is the
On Wed, Dec 13, 2017 at 02:49:39PM +0000, dwight via cctalk wrote:
When I was at Intel, years ago, I recall the
baking was only to repair
the retention of the EPROMs. It was not to fix random failures.
It sounds like your EPROMs have various failures that wouldn't be helped
Each time the EPROM is programmed, there is a slight increase in the
leakage of the floating gate. This was typical after thousands of
program/erase cycles. Baking them repaired the damage to the insulating
layer that was damaged.
I don't think these chips have been reprogrammed many times. It seems more
age related, affecting some brands/models in my spares but not others.
The failure mode is the chips erase successfully, but any attempt to
program them fails, and they still test blank and read back "ffff...".
Some of these were chips I erased years ago before putting in my spares
drawer, and some had fine working code on them, but I erased them to
re-program with a newer version of software on them, to discover I could
My stash of TI and NEC 2732s seem to have the disease, but my ST,
Mitsubishi, and several others program fine.
In the case of a bunch of 2732s, I have tried both a vintage DataI/O 29A
programmer and a modern Batronix programmer, with the same results.
I don't think I have a programmer problem.
I still swear someone in the late 80's had me baking EPROMs in an oven
to restore their programability, but I don't remember the specifics. I
tried a few at 450F for 15 minutes, but they still won't program.
Are you positive you have the programming voltage right? I have a box of
really old ones and every time I have to research a little to find the
right voltage for different brands. All 27128's are not the same, for
example. Some are 12V, some may be 25V (for example). My programmer only
has one setting in the software, and I have to change jumpers to modify
programming voltage. My USB programmer won't touch any of the old ones
because I assume it can't provide enough voltage/current for them.