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Thread: UV Erasing tms27c256

  1. #1
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    Default UV Erasing tms27c256

    So I decided to re-purpose some tms27c256 Roms that came from an old Zenith 286 sportster (battery liquefied the unit and it was ruined)
    I am a novice when it comes to this and I understand the theory but I could use some clarification. I have read 30 minutes to 1 hour usually works for High intensity (whatever that can be explained as) UV lamps. I am using my 80 watt Large LED UV lamps I use for retrobrighting. I tried 30 minutes, 1 hour, and 24 hours. The Roms still show all the data they started with when checkingwith my Mini pro. Does it require more than 24 hours under these lamps?

    This might sound silly but since these were programmed in the mid 80's is the data now permanent?

  2. #2
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    "LED UV lamps" may be the source of your problem. UV EPROMs generally require exposure of 254 nm or thereabouts. Longer wavelengths won't do it, at any amount of time.

    Do you smell ozone when you run your LEDs?

    What does the spectrum of your LEDs look like?
    Last edited by Chuck(G); July 13th, 2020 at 07:58 AM.

  3. #3

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    yeah I'm with Chuck, sounds like a wavelength issue

    you need to use the UV bulbs advertised as being for sanitizing

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    As a related note: A lot of Chinese "Corn" LED lamps are being sold as UV-C units. They're not. Big Clive had a post on YT not long ago where he tests UV LED lamps.

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    If you bought those cheap, they won't work. The price of UVLED's goes up exponentially as the Angstroms go down. AFAIK there are very few "true" UV-C LED's yet and they are costly.

    I'd like to know how they intend to package them because UV-C will just kill plastic.

  6. #6
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    Quote Originally Posted by Chuck(G) View Post
    "LED UV lamps" may be the source of your problem. UV EPROMs generally require exposure of 254 nm or thereabouts. Longer wavelengths won't do it, at any amount of time.

    Do you smell ozone when you run your LEDs?

    What does the spectrum of your LEDs look like?
    No no ozone, but I am pretty sure my fluorescent UV "C" bulbs did.
    bought these: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
    says wavelength is 400-410nm
    I still have one lamp with fluorescent bulbs left. (same ones used in bug lamps) I tend to only use it on small parts and not much as the bulbs are getting harder and harder to source.

    I take it Direct Sunlight is not advisable and will ruin the ROMS?

  7. #7
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    Quote Originally Posted by Slob View Post
    If you bought those cheap, they won't work. The price of UVLED's goes up exponentially as the Angstroms go down. AFAIK there are very few "true" UV-C LED's yet and they are costly.

    I'd like to know how they intend to package them because UV-C will just kill plastic.
    UV-C does indeed kill plastics. I still have some sylvania UV-C germicidal fluorescent bulbs I was experimenting with when setting up retrobright indoor tanks. Within 24 hours is turned the lens a brownish yellow. Anyway none of these are UV-C

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    Quote Originally Posted by maxtherabbit View Post
    yeah I'm with Chuck, sounds like a wavelength issue

    you need to use the UV bulbs advertised as being for sanitizing
    well Like I mentioned, I still have some sylvania UV-C germicidal bulbs and a Fluorescent lamp to use them in. If this is my only method how long are we talking for exposure time?

  9. Default

    Quote Originally Posted by Chuck(G) View Post
    Longer wavelengths won't do it, at any amount of time.
    I have reason to doubt this, since I was successful in erasing some with an LED nail polish dryer. It took about 4 days, but it worked. Same thing with a fluorescent bulb for lizard cages from the pet store. Or maybe even a bulb specified for 380nm may emit a small percentage of 250nm or whatever is actually needed...

    Using the correct thing is much quicker when available, but if someone is determined to use the wrong thing there is still hope I heard that sunlight also works, on similar timescales, but haven't tried it myself (this area is not known for sunny weather)

  10. #10
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    Could be that there's just enough short-wave UV-B there to do some work. Direct bright sunlight is supposed to take about a week, but I've never tried it.

    Or you could wait 200 years and the trapped charges will likely have dissipated on their own, even in complete darkness.

    With a germicidal lamp at close distance (an inch or two), 15-30 minutes should do the job.

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