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Thread: Erasing UV EPROMs

  1. #1

    Default Erasing UV EPROMs

    Hello All,

    By definition can UV EPROMs (i.e. those with a window) only be erased by UV light? I have a cheapo G540 USB programmer and it has an "erase" function which I believe seems to run on an EPROM and completes OK. But reading the chip shows the old content. I have a UV eraser that is not easily accessible at the moment and was trying to get around having to dig it out. Assuming UV light is it, are the old stories about sunlight true? Can I just leave the chip out for a few hours in CA sun and have it be erased? Just wondering...
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  2. Default

    Your programmer wont erase EPROMS (EEPROMS is a different story). In my experience leaving the eprom outside for one week will erase the data fully, I live in a sunny location.

  3. #3
    Join Date
    Dec 2010
    Location
    Seattle, WA
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    Default

    From an ST M27C256B datasheet, as one example:

    ERASURE OPERATION (applies for UV EPROM)

    The erasure characteristics of the M27C256B is such that erasure
    begins when the cells are exposed to light with wavelengths shorter
    than approximately 4000 . It should be noted that sunlight and some
    type of fluorescent lamps have wavelengths in the 3000-4000 range.
    Research shows that constant exposure to room level fluorescent
    lighting could erase a typical M27C256B in about 3 years, while it
    would take approximately 1 week to cause erasure when exposed to
    direct sunlight. If the M27C256B is to be exposed to these types of
    lighting conditions for extended periods of time, it is suggested that
    opaque labels be put over the M27C256B window to prevent unintentional
    erasure. The recommended erasure procedure for the M27C256B is
    exposure to short wave ultraviolet light which has wavelength 2537.
    The integrated dose (i.e. UV intensity x exposure time) for erasure
    should be a minimum of 15 W-sec/cm2. The erasure time with this dosage
    is approximately 15 to 20 minutes using an ultraviolet lamp with 12000
    W/cm2 power rating. The M27C256B should be placed within 2.5 cm (1
    inch) of the lamp tubes during the erasure. Some lamps have a filter
    on their tubes which should be removed before erasure.

  4. #4
    Join Date
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    Default

    I think the "erase" function on your programmer is intended for EEPROMs, not UVEPROMs. The latter are erased with UVC wavelengths (approximately 280-100 nm). The atmosphere filters out most of the shorter wavelength sunlight, so you're probably talking days, not hours. That window on the EPROM is made of quartz (fused silica) because it can pass shorter UV wavelengths.

    Most EPROM erasers typically use "germicidal" lamps of fairly low power (e.g. 6-9 watts), which should be inexpensive to obtain, unless the Covid-19 folks have snatched them up. My first EPROM eraser was made of a coffee can and a clothes dryer UV lamp. It worked fine.

    I note from the above post that the range is given as 400-300 nm, same ballpark.

  5. #5

    Default

    Mine is a toothbrush sanitizer I got from ebay for $10

  6. #6
    Join Date
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    Default

    If you've got one of those CPAP sanitizers, that should work as well.

  7. #7

    Default

    Yeah - one week is not realistic. Time to go digging in the boxes in the garage to get the UV eraser out. Thanks for all the info guys especially the datasheet info.
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  8. #8

    Default

    Quote Originally Posted by maxtherabbit View Post
    Mine is a toothbrush sanitizer I got from ebay for $10
    Hmm.. I have one of those too I wonder if that will do... How long do you typically leave it in there?
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  9. #9
    Join Date
    Apr 2018
    Location
    Los Angeles, CA
    Posts
    949

    Default

    I think I'll test this myself out of curiosity, since there's not much else to do while many of my china packages for projects appear to have been sitting in customs (or whereever) for a month. That said, I do have an eprom eraser already so I wouldn't ever do this in real life.

    BTW, this post (convert to english) is interesting on the topic.

    https://www.elektroda.pl/rtvforum/topic3236341.html
    -- Brian

    Systems: Amstad PCW 8256, Apple IIe/II+/GS/Mac+/Mac 512k, Atari 800/520STFM, Commodore 64/128/Amiga 3000/PET 4032/SX-64, IBM PS/1 2121-B82, Kaypro II, Osborne 1, Tandy 1000 SX, TI-99/4A, Timex Sinclair 1000, TRS-80 Color Computer 3/Model 4 GA

  10. #10

    Default

    Quote Originally Posted by Shadow Lord View Post
    Hmm.. I have one of those too I wonder if that will do... How long do you typically leave it in there?
    About 15 minutes seems to reliably blank most things

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