How do you know EEPROM chips are good

Discussion in 'General Electronics Chat' started by SamEricson, Apr 26, 2015.

  1. SamEricson

    Thread Starter Member

    Apr 25, 2015
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    When troubleshooting circuit boards that have multiple EEPROM chips that have programs or codes on them but you don't have the schematics to the circuit boards or the EEPROM chip code files.

    How do I test the EEPROM chips to make sure they are good?

    I can use a Universal programmer to do what kinds of EEPROM checks?

    Make sure the EEPROM chip reads and write and test the check sum?

    Since I don't have the program code files for the circuit boards I'm troubleshooting, what can a electronic technician do with boards that have multiple EEPROM chips to test them?
     
  2. Papabravo

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    Feb 24, 2006
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    I don't think there is much you can do. Not without removing the chips from the board. Even if you can get them off the board, they probably have secutity fuses blown to prevent you from reading the contents. People still troubleshoot boards? I thought the economic thing to do was to toss them in the bin.
     
  3. SamEricson

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    Apr 25, 2015
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    Yes they are the EEPROM chips have sockets, I am able to remove the EEPROM chips.
    What can I use to test the EEPROM chips? a universal programmer?
     
  4. Papabravo

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    Feb 24, 2006
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    Do you have a universal programmer?
    Why do you suspect the EEPROM chips are bad?
    Do you know what is supposed to be in them?
    I've heard of people who really need to see inside disassembling the package and dumping the contents with an electron microscope. Sounds like fun.
     
  5. SamEricson

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    Apr 25, 2015
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    I just want to verify if the EEPROM chips are good or bad? how do you verify if they are good or bad?
     
  6. Alec_t

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    Sep 17, 2013
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    How do you define good (or bad)?
     
  7. Papabravo

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    Feb 24, 2006
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    You compare the contents to the original file that was used to program them. That is the only way I know of. Does anybody have a better method?
     
  8. SamEricson

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    Apr 25, 2015
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    Yes but i don't have the original files to these EEPROM chips.

    The only things I can do it put the EEPROM chip in a universal programmer and test the read,write and check sum?

    If the EEPROM can't read or write then the EEPROM chip is bad
    If the EEPROM check sum is flagged then the EEPROM chip is bad

    Do you know any other EEPROM tests i can do?
     
  9. ian field

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    Oct 27, 2012
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    Years ago I encountered a Thorn Consumer CTV with a corrupted EEPROM, the price of a replacement was more than the set was worth.

    Just for kicks, I pulled a same part number chip from a random set laying about the workshop and plugged it in. The front panel micro decided that it had a blank EEPROM and formatted it - I had to do every single service adjustment and save the settings, but it was good as new.

    For run of the mill stuff, apparently some EPROM programmers can retry a flaky bit until it gets a 1 or a 0, past that; you have to roll your sleeves up and study the micro's instruction set - 1000's of lines of code searching for that instruction that doesn't quite fit.
     
  10. Alec_t

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    But if you write to the chip won't you destroy the stored software?
     
  11. SamEricson

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    Apr 25, 2015
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    Ian Fields how would you test circuit boards that had a bunch of EEPROM chips and was asked to verify each EEPROM chip on that circuit board was good or bad?

    If the EEPROM chip is flaky the check sum would be flagged right?

    Can I use any universal programmer to test all kinds of EEPROM chips?
     
  12. ian field

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    Oct 27, 2012
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    If it has a security bit set - that can only be cleared by a full erase.

    A universal programmer might be able to see a flaky bit that the equipment can't.

    I thought you only got security bits on flash micro's anyway - a secured EEPROM wouldn't be much use to the machine either!
     
  13. Papabravo

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    Feb 24, 2006
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    Point number 2, the checksum, assumes you know how the checksum was calculated and where it is located inside the chip. I don't think you have even a small chance of making a good/bad decision on these EEPROMS.
     
  14. SamEricson

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    Apr 25, 2015
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    What other test equipment do I need to test,check and troubleshoot EEPROM chips?
     
  15. dl324

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    Mar 30, 2015
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    The storage element of an EEPROM is analog and is only guaranteed to hold it's charge for 10-20 years.

    You can test them by reading at low, nominal, and high VCC. If bits have lost sufficient charge, they might read correctly at low VCC, but not nominal. Checking at high VCC will allow you to check program margin.
    Writing is destructive, if you do this, make sure you save the contents. Check sums can be checked if you know the algorithm and what it's supposed to be.
    For starters. Search for the original code and compare what is in yours. Swap EEPROMs with a known good board. If you suspect that the devices are bad, you have to write and read known patterns so you can search for failures.

    Any universal programmer will allow you to read and compare contents in the chip. All should let you change VCC.
     
  16. ian field

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    Put the EEPROM in a reader and try to read it, save the file - then repeat those 2 steps and compare the files, if they differ, its a flaky EEPROM.

    If they differ - you could try several attempts to read, blow the code into new chips and see whether any of them work.

    If you only get clean results, the problem is most likely elsewhere.

    How old is it? - EEPROMS do have a finite retention time.
     
  17. MaxHeadRoom

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    Jul 18, 2013
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    Depends if you mean an existing program is OK or if they are OK after full erasure?
    A full erasure followed by a validity check is a simple procedure for most eprom programmers.
    Most decent programmers with cover all common eproms.
    Many common problems occur because the erasure window has not been covered, I have seen eproms affected where the enclosure door has been left open and exposed to sunlight.
    Max.
     
  18. SamEricson

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    Apr 25, 2015
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    Yes this is what I have been doing

    I use a universal programmer
    1.) read the file from the EEPROM chip
    2.) Then SAVE the file.
    3.) I then erase the EEPROM chip to clear it.
    4.) Then I write the file back to the EEPROM chip.
    5.) I do this multiple times to make sure there not flaky problems
    6.) If you only get clean results, the problem is most likely elsewhere., yes TRUE

    Some circuit boards are from the 80's and 90's circuit boards of various products

    How long are EEPROM finite retention time mostly?

    Also using different universal programmers to test the same EEPROM chips because they read, write, and check sum differently right? each universal programmer has different debugging and flagging errors?
     
  19. ian field

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    Oct 27, 2012
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    And what happens if the first read that you then write back is the flaky one?.....................

    You read the original EEPROM several times to see if you get different output files - if you do; write the files to new EEPROMS and see whether any of them work.

    You keep the original EEPROM in case you have to try again - if you've erased and re-written the original, that's it; you've burned your bridges!
     
  20. #12

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    Nov 30, 2010
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    So, do I have this correct? You want a list of all equipment that might be used on any EEPROM as far back as the 1980's, how to use each one, including how they do reads, writes, checksums, debugging, and flagging of errors.

    I think somebody is writing that book right now. He will post it soon.
     
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