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Thread: IBM 5160 - Troubleshooting power issues

  1. #11

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    Quote Originally Posted by BakaOsaka View Post
    ......I tested the voltages according to this page, and I got the following:

    P9
    P6: +4.74v
    P5: +4.74v
    P4: +4.74v
    P3: 0.00v

    P8
    P4: -11.58v
    P3: +13.70v
    P2: +4.45v
    P1: +4.45v
    Your +12v line looks too high at +13.70v, I'd double check that measurement, Did you measure for shorts on the board as per Modem7's site. Edit: I should read the thread properly, I see you did.

    I suppose it is possible that the BIOS chips are still defective. I assume this could cause these symptoms?
    Yes it's possible that the BIOS chip in U18 is faulty as well, Can you burn your own Eproms ?, As the board has the 11/08/82 BIOS you can remove the Eprom from U19 and the board will still post without it but will throw an error, You can't do that with the later BIOS's though.
    Last edited by Malc; May 14th, 2020 at 11:06 PM.

  2. #12
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    Obviously, the lack of -5V is due to the fact that your ATX PSU does not generate -5V. However, as I wrote earlier, the IBM 5160 motherboard itself, only requires +5V.

    So, you have an 'appears to be dead' motherboard. Many many possibilities. The failure of any of about 80% (arguably) of the motherboard's chips can cause that symptom.

    Maybe the POST is starting, maybe not. If it is starting, then because you hear no beeps when you do the 'minimum diagnostic configuration' of [here], then the POST is not getting as far as step 21 in the POST sequence shown at [here].

    The basics:

    * Thorough visual inspection.
    * Socketed chips: Look for chips that have been inserted in the wrong orientation.
    * Socketed chips: Remove all socketed chips and inspect the pins, looking for pins that have been bent up under the chip. This action also effectively re-seats the chips.
    * Swap out RAM bank 0 chips for a set of known good chips.
    * Swap out all other socketed chips for known-good chips.
    * Use a Landmark/Supersoft diagnostic ROM in place of BIOS chip U18. See [here]. Note the special video card requirements, although, speaker beeps can be informative.
    * Socketed chips: Look for 'incorrect' chips inserted by a previous owner. E.g. A VCF member found that on his 5150 motherboard, the wrong type of RAM chip had been put into one of the sockets.


    Beyond that, 'diving deep' is required. E.g. Using an oscilloscope to verify that clocks are being generated. Looking for the presence/absence of other activity.

  3. #13
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    Quote Originally Posted by modem7 View Post
    However, as I wrote earlier, the IBM 5160 motherboard itself, only requires +5V.
    Oops. And the POWER GOOD signal.

  4. #14
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    Hi all, thanks for your replies. I'm still troubleshooting this board, currently without much luck.
    I've bought a set of new RAM chips - MN4164P-15A's - And fitted these to bank 0. The machine still failed to POST, showing no signs of life.
    I also tried replacing the CPU with an NEC V20, and again had no luck. I also removed the ROM from U19 with the same result.

    My next planned steps are to use the suggested diagnostic ROM to pinpoint the cause, however I will have to purchase pre-flashed ROMs which will take some time. In the mean-time, I have hooked my logic probe up to the motherboard. Is there a list of signals I can check that may help limit the cause of this issue?

  5. #15
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    Quote Originally Posted by BakaOsaka View Post
    My next planned steps are to use the suggested diagnostic ROM to pinpoint the cause, however I will have to purchase pre-flashed ROMs which will take some time. In the mean-time, I have hooked my logic probe up to the motherboard. Is there a list of signals I can check that may help limit the cause of this issue?
    At [here], see the linked image in step 13. If your probe indicates pulses on pin 13 of the 8253 chip, it means that the CPU has started executing the POST and is getting at least as far as step 13.

    If no pulses on pin 13 of the 8253 chip, then per step 3 at [here], verify that your probe indicates pulses (the 4.7727 MHz clock signal) at the clock pins of the 8088 and 8288 chips.

  6. #16
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    Thanks for the link - Very informative.

    Pin 13 (OUT 1) on the 8253 is high - No pulse. Pins 9, 15 and 18 (CLK 0/1/2) are all pulsing.
    Pin 8 (CLK) on the 8284A is pulsing. Pin 10 (RESET) is low.
    Pin 19 (CLK) on the 8088 is pulsing. Pin 21 (RESET) is low.
    Pin 2 (CLK) on the 8288 is pulsing.

    So it looks like it's at least reaching step 8 at this page - Is that correct?

    1980s_john was kind enough to flash a Landmark Diagnostics ROM (This image) to an L27C256D - I fitted this to U18 and still saw no response - ie. no speaker beep at all. I'm assuming this means it's failing before it can even execute the diagnostics ROM?

  7. #17
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    Quote Originally Posted by BakaOsaka View Post
    Thanks for the link - Very informative.
    Lots of other informative 5160 information in the IBM 5160 section of minuszerodegrees.net

    Quote Originally Posted by BakaOsaka View Post
    Pin 13 (OUT 1) on the 8253 is high - No pulse. Pins 9, 15 and 18 (CLK 0/1/2) are all pulsing.
    Pin 8 (CLK) on the 8284A is pulsing. Pin 10 (RESET) is low.
    Pin 19 (CLK) on the 8088 is pulsing. Pin 21 (RESET) is low.
    Pin 2 (CLK) on the 8288 is pulsing.

    So it looks like it's at least reaching step 8 at this page - Is that correct?
    Yes.

    Although, there is a possibility that something earlier may not be happening properly. Regarding "When the 8088 CPU leaves the reset state, it starts execution at address FFFF0." The data sheet for the 8088 includes in its description of its reset pin, "The signal must be active HIGH for at least four clock cycles." In the IBM 5160, four clock cycles equates to 840 ns. The oscilloscope measurement at [here], for one of my PSU's, shows that the reset-high-minimum-time requirement of 840 ns is exceeded by a looooooong shot (300 ms).

    It would be good for you to verify that the reset pin of the 8088 is initially high, then goes low. If I hook my logic probe up to the reset pin of the 8088, then power on the PSU, I see the probe indicate HIGH (for less than a second) then indicate LOW.

    Quote Originally Posted by BakaOsaka View Post
    1980s_john was kind enough to flash a Landmark Diagnostics ROM (This image) to an L27C256D ...
    I confirm that that is the right image.

    You have an early 5160 motherboard. L27C256 does not appear in the table at [here], and so there is a remote possibility that the L27C256 is unsuitable for the early 5160 motherboard. Maybe someone has proven it fit for the early 5160 motherboard.

    Quote Originally Posted by BakaOsaka View Post
    ... I fitted this to U18 and still saw no response - ie. no speaker beep at all. I'm assuming this means it's failing before it can even execute the diagnostics ROM?
    So many possibilities. Per the image at [here], does your logic probe indicate pulses on the /CE pin of U18 ?

  8. #18

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    Quote Originally Posted by modem7 View Post
    .... and so there is a remote possibility that the L27C256 is unsuitable for the early 5160 motherboard. Maybe someone has proven it fit for the early 5160 motherboard......
    I have a bunch of TMS27C256 Eproms which have L27C256D / E printed underneath the chip, I can confirm the TMS27C256 is not compatible with all the IBM boards.

    To the OP, Where on the Eprom is L27C256D printed, Top or bottom, If it's the bottom what does it say on the top ?

  9. #19
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    Quote Originally Posted by modem7 View Post
    It would be good for you to verify that the reset pin of the 8088 is initially high, then goes low. If I hook my logic probe up to the reset pin of the 8088, then power on the PSU, I see the probe indicate HIGH (for less than a second) then indicate LOW.
    I can confirm that Pin 21 (RESET) is initially high, and goes low shortly after (ie under a second).

    Quote Originally Posted by modem7 View Post
    So many possibilities. Per the image at [here], does your logic probe indicate pulses on the /CE pin of U18 ?
    With the either the original BIOS ROM or the Landmark ROM fitted to U18 the state of Pin 20 seems inconsistent. Sometimes it will pulse a few times at power-on before staying high, and sometimes it will pulse consistently until I remove power. The pulsing also seems inconsistent - For example, on the cases where it pulses a few times it may pulse at a much faster rate than it does when it's pulsing consistently.

    Quote Originally Posted by Malc View Post
    To the OP, Where on the Eprom is L27C256D printed, Top or bottom, If it's the bottom what does it say on the top ?
    On the bottom - The full text is:
    L27C256D/8163027
    KOREA 26

    And on the front it says:
    TMS
    27C256-25JL
    LDE 8826

  10. #20

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    Quote Originally Posted by BakaOsaka View Post
    On the bottom - The full text is:
    L27C256D/8163027
    KOREA 26

    And on the front it says:
    TMS
    27C256-25JL
    LDE 8826
    Do you know if your Eprom was tested and confirmed working before being sent to you.
    Sometime today i will pull out an early 5160 board and refresh my memory, IIRC the TMS27C256 Eproms i have did not work in the Early 5160 board, The board appeared Dead. I also seem to remember having the same problem if i tried them in a 5170 or 5162.

    Many years ago i bought several tubes of Eproms NOS and cheap, These TMS Eproms were included and the only ones i had problems with on IBM 5160 / 5162 / 5170 Boards.
    Last edited by Malc; June 7th, 2020 at 01:01 AM.

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