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Thread: Yup, another IBM 5160 failed motherboard

  1. #1

    Default Yup, another IBM 5160 failed motherboard

    I have a 5160 XT 64-256 motherboard.

    Last time I tried to swap the CPU with NEC 12 Mhz one and it did not work. So I tried the original one and it still did not work. Motherboard appear "dead".

    Procedures done so far:
    - minimum diagnostics setup does not work.
    - the CPU is OK, I tried it on another motherboard.
    - I checked the 40 pins of the CPU socket for connection with the other side of the motherboard - all connected. A bad socket or a damaged one could explain everything.
    - POWER is OK. I powered another motherboard with the same power supply. Voltages are OK.
    - I changed capacitors: C58, C59, C56, C54, C68. Middle pin is +, outside is -. Longer leg of the capacitor is + (there is a + also on it)
    - I re-socketed the entire 9 x 4 = 36 memory chips
    - I exchanged the memory chips from BANK0 and BANK1

    What else can be done ?

    I have a hard time identifying the memory chips.
    IMG_20201122_212018.png
    Last edited by tonata; November 22nd, 2020 at 01:01 PM.

  2. #2
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    Quote Originally Posted by tonata View Post
    Last time I tried to swap the CPU with NEC 12 Mhz one and it did not work. So I tried the original one and it still did not work. Motherboard appear "dead".
    So, the motherboard was working before you put in the NEC V20 CPU ?

    Quote Originally Posted by tonata View Post
    - POWER is OK. I powered another motherboard with the same power supply. Voltages are OK.
    So, on the faulty motherboard, the voltages and POWER GOOD signal are good (per [here]) ?

    Quote Originally Posted by tonata View Post
    What else can be done ?
    Do you have a Supersoft/Landmark Diagnostic ROM ?
    If so, does it show anything ?

    If not, do you have another BIOS ROM chip to try ?

    Per [here], do you have the means to see if the CPU and 8288 chip are getting a 4.77 MHz clock signal ?

  3. #3
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    Quote Originally Posted by tonata View Post
    I have a hard time identifying the memory chips.
    Based on the symbol, the chip maker is Siemens (see [here]).
    A search for "Siemens 8493286" shows some hits, some including "DIP16", and so I suspect that 8493286 is the part number.

    Siemens' normal chip for ths application is the HYB4164. Maybe IBM had Siemens label their HYB4164 as the IBM part number of 8493286 ?
    And IBM may have had other makers do the same thing, e.g. "intel 8493286" appears at [here].
    "8493286" also appears on these forums at [here].

  4. #4

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    Yes. It was working. But then I did not test immediately before changing the CPU. So 10 days before changing the CPU was working.

    Yes I checked the voltages per here

    I do not have EPROM writer or Diagnostics ROM. I have ROMs from another IBM 5160, but still they are not diagnostic.

    I have a logic probe and multimeter. Maybe I can access another equipment if I know exactly what I need to see the clock signal.

    Quote Originally Posted by modem7 View Post
    So, the motherboard was working before you put in the NEC V20 CPU ?


    So, on the faulty motherboard, the voltages and POWER GOOD signal are good (per [here]) ?


    Do you have a Supersoft/Landmark Diagnostic ROM ?
    If so, does it show anything ?

    If not, do you have another BIOS ROM chip to try ?

    Per [here], do you have the means to see if the CPU and 8288 chip are getting a 4.77 MHz clock signal ?
    Last edited by tonata; November 22nd, 2020 at 03:12 PM.

  5. #5
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    Quote Originally Posted by tonata View Post
    I have ROMs from another IBM 5160, but still they are not diagnostic.
    A faulty BIOS ROM is a possibility, so try a BIOS ROM from another 5160.

    Quote Originally Posted by tonata View Post
    I have a logic probe and multimeter. Maybe I can access another equipment if I know exactly what I need to see the clock signal.
    Your logic probe should show alternating signals, such as clocks.
    Use it to see how it behaves when measuring the 4.77 MHz clock on your good 5160 motherboard.
    It will not tell you the frequency, but it will give you confidence that the clock is present.

  6. #6

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    So the 8288 is next to the power supply and the FPU. It is U8.
    In your link link it is 8284A. It is not 8288, bit I suppose it is OK.
    So pin 2 of the 8288 gives clock on the probe.
    Pin 19 on the CPU gives clock also.

  7. #7
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    Quote Originally Posted by tonata View Post
    I do not have EPROM writer or Diagnostics ROM.
    The people/companies at [here] can create the ROM for you.

  8. #8
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    Quote Originally Posted by tonata View Post
    So the 8288 is next to the power supply and the FPU. It is U8.
    In your link link it is 8284A. It is not 8288, bit I suppose it is OK.
    The link shows the 8284A generating the 4.77 MHz clock, with the "CPU, 8288, NPU" receiving that clock.

    (The NPU {8087} socket does not need to be checked. The NPU, if present, is not involved in the starting of the 5160.)

    Quote Originally Posted by tonata View Post
    So pin 2 of the 8288 gives clock on the probe.
    Pin 19 on the CPU gives clock also.
    Giving you good confidence about the 4.77 MHz clock.

    Refer to [here]. Does your logic probe show pulses on pin 13 of the 8253 chip. If it does, it means that the POST has started (reaching at least step 13 at [here]).

    Tried another set of IBM BIOS ROM's ?

  9. #9

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    I checked with the other ROM chips. It did not work. But then these other ROM chips are from upgraded MB from 16-256 to 256-640 by IBM. So it is another version of the ROMs 1986 compared to 1983 (the failed one) and this upgraded MB has some extra cables around the ROM chips. So I am not sure it was compatible?

    Pin 13 gives red 5 V, instead of pulses. So definitely a problem?

    Can I check if the CPU is halted?
    Last edited by tonata; November 23rd, 2020 at 01:28 AM.

  10. #10

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    PB7 on 8255 shows no state. The logic probe diodes are all dark.
    It is supposed to be high?

    And when I say that there is "clock" actually 3 diodes are on: red, orange (pulse) and green. It is not just blinking the orange one (pulse). Maybe when the frequency is too high is like that. It is the 3 instead of a pulsing orange diode.
    Last edited by tonata; November 23rd, 2020 at 01:28 AM.

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