Programming Eproms:Yikes!

by Bob Roberts

The year 2000 has arrived, bringing with it the advanced & less expensive technologies unthought of only a few short years ago. It is now affordable for an arcade game collector, operator, or nowadays, just about anyone in any field...since computer driven devices have begun their worldwide own & use an eprom programmer. I think we are close to the time when we can actually say if it is a product that can be taken apart, you'll find an eprom inside!

In keeping with my nontechnical jargon newbie policy, I am not going into what an eprom is or does, but I am going to quickly address the issue of using this new found toy to program older eproms used in Classic video arcade games and other equipment from days gone by.

As more & more newbies obtain eprom programmers, a problem has arisen, and since I have been using good old faithful 1980s eprom programmers for years now, I'm not sure why, but I would guess that you need to setup your own profile with programming voltages for the various chips being programmed with these less expensive units. It must be something like this, as herein lies the problems. Many are asking me what the program voltage needs to be on certain brands, or asking what it should be for a house number/name... this is a number or name put on the chip by the mfger for the end user,e.g., Atari may have a 2764 that is labeled 137-093 or a Compaq computer may have a 2764 labeled simply as Compaq & with no other numbers or markings on it.

These are the people that know that some eproms require a different programming voltage. Now there are many who do not know this, and will therefore sometimes burn up a whole tube of eproms during their experimentations of burning (the in crowd's word for programming) the eproms, and this is exactly what occurs....the eproms are smoked & rendered unusable & ready for file 13.

As a general ROT, eproms from 27128A up to 27C160(16 megs) will program at 12.5 volts, but prior to those Jamma-era eproms the programming voltages varied widely. Beginning right here with the 27128, without the suffix *A* it's programming voltage is 21 volts! Hello! Newbie pops a 27128A in the socket & sets programming voltage at 21 volts instead of 12.5 volts, and we're having smoked chips for lunch! Where's that file 13 trash can?

Here's a chart for the most likely candidates for smoking, and I'll tell you how I handled this issue below, although it was never a problem for numbered eproms.

Programming Voltages
253225 volts
2532A21 volts
273225 volts
2732A21 volts
276421 volts
2764A12.5 volts
2712821 volts
27128A12.5 volts

Yes, this was a problem with house marked chips in the old days, as well. No one ever told me a way to tell the difference between the clearly marked eprom pulls and the sometimes no marking at all eproms that were mixed in the tubes. My first thoughts were to simply try it at the lowest setting to begin with. The results, keeping in mind that I use antiques & your results may vary, were as follows:

A) It programs at the lower voltage & the checksum verifies that it has done so successfully.

B) It programs at the lower voltage but there is a chksum error, in which case, I attempt to patch using the higher voltage. Most times this is successful, but occasionally the eprom will need to be erased & reprogrammed at the now known higher voltage.

C) The programmer tosses up some sort of eroneous error such as "device not erased", "chip not in socket", or sometimes it even says "wrong device selected", a good indication that you indeed need the higher programming voltage, which you can simply select at that time & continue on to a successful programming.

This has always worked for me & saved countless unknown eproms, regardless of whether the numbers simply faded away to nothing, or there was a house name or number on them.

I hope this saves a few more of the eproms that are slowly getting harder and harder to find.

Happy Gaming..............

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