Connect with us

Replacing 80xx series ICs?

Discussion in 'Electronic Components' started by DaveC, Feb 24, 2006.

Scroll to continue with content
  1. DaveC

    DaveC Guest

    It's in an old (mid-80's) industrial machine. The French mfr. is out of
    business. The circuit I'm trying to resurrect takes a digital measuring
    encoder as input and displays the measurement on 7-segment LED displays.
    Display went wonky for a few weeks, then went blank, entirely. DC voltages
    and ripple are all good. Tried reseating socketed components; no joy.

    Lacking any documentation, I'm going to try some "shotgun" troubleshooting by
    replacing the major components on the board (they're socketed).

    Large components include:
    All parts NEC mfr.

    When replacing with components available today, what are my limitations? (For
    example, I know "H" means HMOS, and that is a "must".) What else should I be
    careful re. the letter digits of the p/n's when selecting parts with the same
    numerical digits of the p/n's?

    I know that the 8279 is a programmable controller, so replacing that without
    having the source code to program it with, is out of the question.

    Just trying to help a client keep this otherwise good machine in service and
    avoid "binning" it.

  2. Opps my bad, looks like the 8279 is a programmable keyboard I/O chip.
    So you should be able just to pop one in. (assuming that's what's wrong
    with the device)

  3. DaveC

    DaveC Guest

    Thus spake William at MyBlueRoom:
    This is what I need help determining. If this is a "production programmed"
    device (burned at time of manufacture), it's a deal-killer for my customer --
    finding a programmed replacement is pretty much not going to happen.

    But if this is a "dynamically programmed" device (ie, counters are loaded at
    run time and reset by external devices), I presume that off-the-shelf it will
    replace the suspect one in the machine.

    Is the 8279 a one-time programmed device?

  4. DaveC

    DaveC Guest

    Thus spake William at MyBlueRoom:
    Oh, you answered my question while I was posting another message to ask you
    this very question. (Such is the down-side of asynchronous communications!)

  5. Pooh Bear

    Pooh Bear Guest

    It appears not to be.

  6. Pieter

    Pieter Guest


    All those parts are still available in the market.

  7. nospam

    nospam Guest

    No, it is just a peripheral with some registers to 'program' its function.
  8. bg

    bg Guest

    DaveC wrote in message
    I do believe that the 8279 is not a programmed device. I could go look it
    up, but that would take work!
    The 8279 was often used for keyboard input and display output. The display
    will be multiplexed. There
    should be a BCD to seven segment converter chip that drives all of the
    displays in parallel. Then each display will have a power transistor that
    switches Vcc on for that display. The power transistors on signal is sync'd
    to the BCD word so that the data appears on the correct display. Make
  9. Arfa Daily

    Arfa Daily Guest

    It seems to me that everyone is "going off on one", before the OP has
    applied at least basic proper fault finding techniques. Before going in
    shotgun and replacing parts that - trust me - seldom if ever go faulty, you
    should first check that the 5v supply is absolutely good - voltage, ripple
    AND noise, that the reset generator is working correctly, and that most
    importantly, the system clock generator is running, and producing a correct
    amplitude and frequency, signal. Also that any following clock distribution
    buffers are working.

    If none of those checks turn up the problem, and in at least 80% of cases on
    this old simple logic, they will, then the next move is to download a
    datasheet for the display controller, and figure why it's not driving the
    displays. The required inputs are not many, and not complex, and require
    only a 'scope to verify.

    From years of experience repairing electronic equipment, I can tell you that
    blanket replacement of components in the fond hope of hitting the right one,
    is about the worst approach that you can take, and likely to result in more
    problems than the probably simple one that you had in the first place.

  10. linnix

    linnix Guest

    Perhaps the local fea market. Look for old 8 bits micros. The 8085
    is an old 8 bits micro, so there must be an EPROM somewhere.
    Unfortunately, EPROM data are not designed to last for 20 years. It's
    amazing to have lasted so long already. My first bet is the EPROM
    losing contents. Unless you have a copy of the data somewhere, forget

    Sound like this is a frequency counter/display or something. A single
    chip micro (AVR or PIC) can do the same.
  11. Wild Bill

    Wild Bill Guest

    It sounds as though the instrument is a Digital Readout display
    associated with machining or other production equipment.
    I don't have much advice for troubleshooting other than what's already
    been suggested by Arfa.
    It's been too many years, and too little practice since my training in
    these types of circuits. I have a completely dead Anilam DRO display,
    and I've had difficulty understanding the circuits even though I have a

    If you proceed with IC replacement, check any datasheets you can find
    to confirm that the operating voltages of replacement parts are the

    Newer used DRO systems are plentiful, depending upon your searching
    abilities. If the linear encoder scales used with the DRO display unit
    are the commly used 5 volt TTL squarewave types, you could possibly
    just replace the display unit with one that's compatible.

    Finding a suitable replacement will probably be a little tougher if the
    DRO display also has outputs for interfacing with NC or CNC machine
    controls, but numerous displays have various optional modules to
    convert inputs to outputs.

    There are numerous surplus suppliers of older ICs in the U.S, and more
    semiconductor sellers are gradually appearing on eBay.

  12. Zak

    Zak Guest

    Reducing the supply voltage a bit (was it? or increasing?) might still
    recover the data.

  13. Do you have any data which supports this claim?

    Most manufacturers claim 100 years or more at normal temperatures.

    Best regards,
    Spehro Pefhany
  14. Yes.

    Best regards,
    Spehro Pefhany
  15. All of those parts were originally from INTEL. NEC was a second
    source. What type of RAM does it use?

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  16. Erik Baigar

    Erik Baigar Guest

    ....also had good experience with carefully cooling
    the EPROMS during readout...

  17. When you say EPROM, you mean those chips with the little transparent window
    that could be erased with special UV light?If yes, could this just happen
    with long exposure (many decades) to normal sunlight (even if dim in the
    bowels of the machine).I strongly doubt though, that you could find nowadays
    labs with the UV light and programm devices to programm (again) those chips,
    now that flash chips are so common and cheap (EEPROM).
    Are there any chips with the characteristical transparent window?
  18. linnix

    linnix Guest

    People who made these claims in the 80s are mostly retired or dead.

    Can't find any typical EPROM (2716 or 2732) used in the 80s. A newer
    one like AT28C16 says data retentions of 10 years. If you want to bet
    $1 per year, we can find an independent engineer for verification.
  19. Pieter

    Pieter Guest

    There are still lots of devices in older stocks available. And for
    many devices replacement parts have been created by others.

    I just did a quick search and found hundreds of the D8085HC of NEC at
    my contacts. It is expensive to get 1 part due to the shipment costs,
    but it is possible. I havent searched the other partsm, but I am
    certain they are available too.

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day