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EPROM over erasing

Discussion in 'Electronic Repair' started by Slater, Aug 17, 2012.

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  1. Slater

    Slater Guest

    Is it possible to damage an EPROM by exposing it to UV light for too
    long? What if a portion of the EPROM stays unprogrammed ('FF') and the
    chip goes through some program-erase cycles? The unprogrammed area
    should fail sooner or later, shouldn't it?
  2. Oh no, that`s an ultra secret: burn before reading!


    Saludos (an alle Vernünftigen, Rest sh. sig)
  3. Lee Gleason

    Lee Gleason Guest

    I left some 25C64's In my manually controlled (that is, no timer) UV
    eraser for a couple of weeks, when I forgot to turn it off. They all still
    programmed and worked fine.
  4. mike

    mike Guest

    What if a portion of the EPROM stays unprogrammed ('FF') and the
  5. c4urs11

    c4urs11 Guest

    Somewhere in the 80s I salvaged a proprietary controller in a steel sheet
    cutting machine using this. We were rushing a repair late at night in the
    middle of nowhere in France. About three sticks managed to wipe 8 devices.
    It needed some convincing the customer though, he believed I was joking.
    The nicest part was the French cuisine afterwards ;-)
  6. Slater

    Slater Guest

    I meant another thing: what will happen if a chip undergoes several
    write/erase cycles where an area is intentionally left unprogrammed
    every time? It's like erasing it over and over.
    Probably nothing, I think. It must have happened quite often that some
    byte (or bit, why not?) would always be unprogrammed at every cycle in
    the prototyping process, so it shouln't be a problem.
  7. Joining this late, I want to mention that the 27C series EPROMS can still
    be bought. You can buy them from China for about $2 each including postage
    for erased and tested "pulls" and new ones can be had for around $45.

    They even come in the small flat packages that are common these days.
    (sorry, it's late at night, and I don't remember their name)

    I specifically needed 27C256's and 27C512's, last summer, so I bought an
    eraser for around $15, a USB programmer for under $50 (including the adaptor
    for flat packaged chips) and a bunch of $2 chips.

    The eraser was an odd combination of a 230 volt unit with a US 120 volt plug,
    and a mechanincal timer with a separate on off switch. I replaced the plug
    with one more appropriate for my needs and just leave the timer in the
    always on position, using an electronic kitchen timer and the on/off switch.

  8. how long can those old ceramic+window things keep their memory? Some spec
    sheets indicate some random number of decades, but is any of this true?
  9. Sjouke Burry

    Sjouke Burry Guest

    Two BBC2 computers and an ARC310 with numerous chips loaded with
    software have survived 20+ years, and still going strong.
  10. Leif Neland

    Leif Neland Guest

    har bragt dette til verden:
    It never worked for me in Denmark, 56N
  11. mike

    mike Guest

    It's an old thread, but I have a story and some time on my hands.

    The erase is not the only problem. Charge can leak in or out
    electrically too.
    I had a TEK 308 logic analyzer that wouldn't run. I fixed it
    by reading the EPROM in my reader, erasing it and putting the
    same bits back in. The data was marginal and wouldn't run
    at speed, but the programmer was slow enough that it worked.
    I replaced the chip anyway.

    The Compaq Aero laptops had a recurrent "motherboard failure".
    I discovered that you could pull the EEPROM, read it
    and reprogram it with the same data. That fixed it for
    a random length of time. In that case, I think the cause
    was that the program line was left floating. Some combination
    of turnon/off transients let random "puffs" of charge into
    whatever address happened to be on the pins and the thresholds
    shifted over time until it failed to boot. I fixed several of them
    by reprogramming. Replacing the chip didn't help.

    I like the roadway analogy.
    Spread gravel on a road. By the end of rush hour, there won't
    be any gravel in the path of the tires. When a tire hits a bit of gravel,
    it causes it to move in some random direction. If that direction
    takes it out of the tire path, it quits moving. Statistically,
    all the gravel eventually gets displaced out of the tire path.
    The gravel got erased.
    But the tires also damage the road. Bits of gravel get embedded
    in the roadway and can't move out. Eventually, the roadway turns
    to gravel and can't support the traffic. Getting just the right
    amount of energy is critical for maximum life. That's why they
    don't want you to drive a tank down a residential street.
  12. Leif Neland

    Leif Neland Guest

    Michael A. Terrell kom med denne ide:
    I know.

    I still have 1500 out of 9000 messages to read, but I'm catching up :)

  13. Leif Neland

    Leif Neland Guest

    Michael A. Terrell forklarede den 25-11-2012:
    I only wanted to go back one year, when I discovered this group.
  14. josephkk

    josephkk Guest

    With the training and experience listed you still call him arrogant? I
    don't think so. More like intolerant of a 'wanna be' blowing smoke.

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