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EPROM and UV-erasing light general questions

Discussion in 'LEDs and Optoelectronics' started by TTL, May 30, 2017.

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  1. TTL


    Oct 24, 2013
    I've recently bought a Minipro TL866CS EPROM programmer and found my old, home-made EPROM eraser from back in the early 80s, so I'm ready to erase and burn some EPROMs, but have some general questions:

    1) I know the type of UV-light used for EPROM erasing is dangerous (I've read it can cause cancer and permanent eye damage), and my home-made metal box isn't completely light-proof and doesn't have any safety switch mechanism as I understand the professional erasers do.
    Just how dangerous is it? Is it safe enough just not to stare directly into the light, or do I have to keep a fair distance and get hold of some special safety glasses as well?

    It's got a small (15cm long) fluorescent tube marked "National GL-4" and some Japanese writing, identical to the one pictured here. According to another page it's a 4W germicidal lamp.

    2) I've heard that subjecting EPROMs to too much UV light can be damaging -is this true? How much is "too much"? I suppose it might be a good idea to erase for a few minutes, check it with the EPROM programmer and continue to erase some more until I find out how long time is needed.

    3) I've read that the data inside EPROMs can get unreliable/damaged after 20 years. Is this because the EPROM itself has a certain lifespan, so it must be discarded when this happens, or will erasing and reprogramming the EPROM with the same data (provided you have a fully working backup) give another 20 years (at least in theory) because the data is "refreshed"?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Just be careful with the UV. A little bit of leakage won't be a huge issue, but don't put your face against the tube. Depending on the wavelength, you can get cataracts, or just really bad sunburn.

    EPROMs store a bit by burying a charge in a "floating gate". Over time this charge can leak away. Erasing and reprogramming the EPROM will refresh it for another 20 years.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Congratulations on reviving EPROM technology here in the day of FLASH and FRAM memory. I too still have one of those ultraviolet lamp erasers and several EPROMs, but the programmer I have was designed to plug into an expansion slot on an IBM-PC and run a program under MS-DOS. So, not much interest here in resurrecting the technology. But, back in the day, I used to keep a half-dozen EPROMs in the eraser, to swap out with a programmed EPROM that didn't quite have all the "bugs" worked out of the program. A real PITA software development environment, compared to what you can do today with a PICkit 3 and a PIC processor and a laptop to run the free Microchip program development environment. If I had more time left on this earth, I might try to build something based on EPROMs and the Intel 8085 microprocessor. Or not. I had enough fun playing with that in the 1980s.

    What do you plan to do with your EPROMs?
    Last edited: May 30, 2017
  4. TTL


    Oct 24, 2013
    Thanks for clearing that up Steve :)
    I'll be sure to keep my distance and not stare into the light. I should probably add a flashing LED to the box, just to indicate that it's on.
    After erasing an EPROM (I tried 10 minutes for starters and the programmer told me it was blank) I re-programmed it successfully! It's great to hear that a new "burning" of an EPROM will result in a "fresh" version of the software and not a malfunction of the EPROM hardware itself. How long do the actual EPROM chips usually last before they need to be replaced?

    hevans1944: Thanks :)
    I have a similar story as yours, only my programmer plugged into an Apple ][+ computer. By adding a ribbon cable I extended the ZIF socket, LED and DIP switches to an external plastic box. The DIP switches were for selecting the type of EPROM to use.
    I used it mostly to re-program EPROMs for the computer itself.
    Using it nowadays is impractical though as transferring the EPROM binary files over to that machine is too much of a hassle. Also it only supported a few EPROM types (2716, 2732 and 2764 as far as I can recall), so a new programmer was in order.
    I'll be using it mostly for maintaining the software versions of old music synthesizers and re-programming sounds of old drum machines.

    A quick question: I hear that buying new EPROMs these days is hard and expensive, and that there's a big used market for this sort of stuff (which I'm sure means "you never know what you're gonna get" to paraphrase a certain first-named Forrest character from a well known movie), and furthermore I've been told there are OTP (One Time Program) ROMs as replacements which are cheaper. Who sells them and are there compatible OTPs to most of the common EPROM types (2716, 2732, 2764, 27128, 27256 etc.)?
    Last edited: May 31, 2017
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Each time you program them you are forcing electrons through an insulating layer. That will cause cumulative damage. However, if you only program them once every 20 years, they will last far longer than you will.

    The best indication would be to look up the datasheet for the device. It may give you an indication of the number of times the device can be reprogrammed. This is typically very conservative as it is essentially a guaranteed minimum. (i.e. you can frequently program it more times than that).
  6. Dreamland.2013


    Mar 26, 2013
    I have hundreds of old eproms 16K up to 1Mb that I will happily give you if you tell me what you need and pay the postage from New Zealand.
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