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Is my 8085 micro actually running?

Discussion in 'Computers, Hardware, and Operating Systems' started by AA7EJ, Mar 30, 2012.

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  1. AA7EJ

    AA7EJ Ham Member QRZ Page

    I have 8085 CPU controlled Cushman CE6000 analyzer.
    I am pretty sure the main controlling CPU board is not working properly.
    For example the _W/R signal appears to be low all the time.

    The problem is that I do not have easy access to the CPU board when installed so I am going to pull it out and test it with just power applied – no interface to the rest of the equipment.

    The question:
    Assuming that I have the processor clock running – what other signals can I use to check if the micro is actually working?

    I only know what it suppose to do on power up – specific display on LCD after 10 seconds and I am not getting it. But the display works - sort off.

    I should be able to trigger on CPU RESET.

    Any help from 8085 guru would be greatly appreciated.

    73 Vaclav
  2. W9GB

    W9GB Ham Member QRZ Page

    Original QRZ Q&A Thread about this Cushman CE6000 analyzer

    Welcome to 1977 !! .....

    The problem MAY not be with the 8085, but with associated 8088/8086 era support ICs.
    Pin No. 40 is used for the power supply (+5v) and pin No. 20 for Ground.
    Pin No. 39 is used as the Hold pin.
    Pins No. 15 to No. 8 are generally used for Address Buses.

    Schematic is almost required for shorten the amount of troubleshooting required

    You will need:

    Datasheet for the Intel 8085 uProcessor

    N8VEM leads a group of computer hobbyists, some are also radio amateurs,
    that build and program (firmware, OS, and applications) for 8-bit processors.

    Last edited: Mar 31, 2012
  3. AA7EJ

    AA7EJ Ham Member QRZ Page

    No problem here - I have TWO logic probes - working Tek 464 dual storage scope.
    I have obtained REAL schematic of the box and happy to report that I already found and fixed with jumper wire one flaky data signal. (Corroded feed thru on PCB)
    This afternoon I have "discovered " a minor discrepancy in the schematic - the CPU circuit board layout has what appears to be a CPU crystal, however, the schematic itself has no crystal and the 5 MHz CLK signal comes from yet not identified source / board.
    After few refresher attempts to relearn the 8085 I am confident that I can use ALE signal to partially verify 8085 operation.
    And that is what I am after right now, working CPU.
    Verifying the data and the address bus signals in proper places will be a cake walk than.
    73 Vaclav
  4. AB9LZ

    AB9LZ Ham Member QRZ Page

    Is there a uv erasable prom in that thing? If so, it may have lost it's mind.

    Btw, if thats the case, you'll "see" lots of seemingly valid logic signals, but the thing will just flat out fail to initialize correctly.

    73 m/4
  5. AA7EJ

    AA7EJ Ham Member QRZ Page

    Yes, it does have an UV eprom and when I was initially working on it I had my work light pretty close to it before I realized the light has UV filter on it hence it must generate some UV under normal operation..
    I have been advised it takes a real UV light , close distance and few minutes to actually erase it.
    So basically I am not sure if it is healthy or gone.
    It suppose to go thru specific display on power up and it does that about 5% of the time.
    But it also should take 10 seconds to stay in that state and it does not do that – even when I use manual RESET.
    But that was when the CPU clock was working at 4.7 MHz.
    I did find some strange levels on one of the true data buses and bypassed some questionable traces.
    Right now I have a manual RESET switch and the LCD goes thru this reset but than the display is not right , but it is always the same. So I figured some other data trace is messed up.
    On top of that – I cannot get any input keys to show up at all.
    But if the eprom is gone – the analyzer goes to the dump because I am sure I will not find another one because it is major pain to open up the box and nobody will do that if their box is OK HI HI HI.
  6. AB9LZ

    AB9LZ Ham Member QRZ Page

    I've seen more than a few instances where the eproms have failed in equipment that old, since i wrote the original code, it was a simple matter of blitzing the chip ( it takes a pretty powerful uv source to erase them so don't be concerned about a desk lamp) and reprogramming, and all was fine.

    The symptom you describe are similar to the problems I had, no display, clocks are running, power is ok, everything seems fine otherwise.

    Not sure what internal physics are at work, but they do go bad.

    73 m/4
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