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Thread: EPROM failure question

  1. #11

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    Quote Originally Posted by falter View Post
    Can an EPROM fail in such a way that you can read it in a reader, but it doesn't actually work in circuit?

    Just dragged out my Hyperion again for one last go over. As I mentioned before it produces a cursor and can do graphics but no text. Whether the character generator EPROM is installed or not the behavior is the same.

    I still think it's likely this video attributes controller, but am trying to eliminate other, easier to obtain parts that it light be.
    I would first of all check the enable signal(s) to the eprom and any possible data bus transceiver that might be in its data path. However yes, I've seen poorly programmed EPROMs (by the modern cheap USB programmers) be marginal enough to have wrong bits when powered at 5V or slightly less and read fine on the proper vintage programmers (hi-lo, data i/o, etc.) that use a 6V Vcc for reading/verifying.

    Frank

  2. #12

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    No
    The speed of the EPROM to read data in a programmer is different than in a system. A weakly programmer cell can be slower to bring the programmed level to the output. In a system that requires more speed, it may fail. As was mentioned before, if you think you have a possible speed failure, you can reprogram your part with the same data.
    Of course, it is not the likely source of your problem but it can help in a few cases.
    Dwight

  3. #13

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    A modern EEPROM reader is able to drive all pins at 5V, while older NMOS chips only output ~3.5V.
    The higher voltage also might make an EEPROM correctly readable inside a reader, while it will be flaky in the system.

  4. #14

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    Quote Originally Posted by Hugo Holden View Post
    I would be interested to know if the "40 year fade" is about what most others have found with UV eproms or did the manufacturers ever say how long it could take ?

    So I'm going to have to "refesh" the ones in the SOL soon it would appear. It makes the idea of the mask or fused ROMs very attractive.
    My '40 years' figure is purely based on the fact that I have already seen some cases of EPROM data fade in equipment getting on for that age, not on any figure quoted in manufacturer's data books. Your mileage will vary: For every device which starts to have problems after just a few decades there will be many others which may retain their data for more than a lifetime. But if you have the means to do so, it is good policy to at least read and make backup file copies of the data in any programmable devices you may have in your retro equipment while it still works, and better still to refresh them by over-programming them with the same data if you have the confidence to do that. The good news is that even windowless one-shot EPROMs can be refreshed in this way, as the device does not need to be erased first.

    I don't know about MASKed ROMs but apparently fusible-link PROMs have their own potential problems, namely 'tin whisker' disease. This problem, in which superfine metallic hairs 'grow' inside the device and eventually cause internal shorts, is more commonly known to affect germanium transistors in metal cans, but apparently fusible link PROMs are also prone to a version of this problem as well.

  5. #15

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    Quote Originally Posted by SiriusHardware View Post

    I don't know about MASKed ROMs but apparently fusible-link PROMs have their own potential problems, namely 'tin whisker' disease. This problem, in which superfine metallic hairs 'grow' inside the device and eventually cause internal shorts, is more commonly known to affect germanium transistors in metal cans, but apparently fusible link PROMs are also prone to a version of this problem as well.
    That is diabolical.

    I am very familiar with tin whisker disease in transistors, it started to affect the germanium AF11X series of transistors in some of my communications radios back in the 1990's. Subsequently the problem got worse and most of the specimens of these transistors have inter-electrode shorts now. I replaced them with the AF178. Recently also Tin whiskers affected one of my prized Tek 2465B oscilloscopes (it took me 1 week to locate it) and also an LG computer monitor in my workshop that has as "Pb free" board with a large fine pin pitch surface mount IC.

    Recently I also wondered whether the same problem could affect silver looking metal topped ceramic IC's, with the cover soldered over the IC die. Recently I had a batch of NOS IC's and one had inexplicable internal shorts and it had never been in circuit. The whole tin whisker problem is very problematic.

    In the case of the LG monitor, I guessed it was the fault before I went looking, because it started off intermittently, became more frequent, the on screen menu coming up randomly, but at the same time, split down the vertical mid-line of the image, the screen contrast changed. In theory at least the fault was happening in two different parts of the circuit simultaneously. A tin whisker was linking them together. That is often a good clue, if its a whisker related problem. But often the whisker might not affect one sub-circuit it links to, or grounds or connects to the supply some other connection, only one intermittent fault is evident, as was the case for my 2465B scope.

  6. #16
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    The dumped data from the EPROM to me looks good and consistent - however I'd need another dump from a working Hyperion to compare and be sure. Haven't found one yet.

    I've found two more sources for the CRT8021-003 chip, but they all have a minimum order of 100 units. Ugh!

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