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Yup, another IBM 5160 failed motherboard

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    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 22, 2020, 01:01 PM.

    #2
    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 ?

    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]) ?

    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 ?

    Comment


      #3
      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].

      Comment


        #4
        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.

        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 22, 2020, 03:12 PM.

        Comment


          #5
          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.

          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.

          Comment


            #6
            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.

            Comment


              #7
              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.

              Comment


                #8
                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.)

                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 ?

                Comment


                  #9
                  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 23, 2020, 01:28 AM.

                  Comment


                    #10
                    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 23, 2020, 01:28 AM.

                    Comment


                      #11
                      Originally posted by tonata View Post
                      Pin 13 gives red 5 V, instead of pulses. So definitely a problem?
                      It is informing you that either:
                      * The POST is not starting, or
                      * The POST is starting, but not getting as far as step 13.

                      Originally posted by tonata View Post
                      Can I check if the CPU is halted?
                      Yes, but that will not inform you of what caused the halt, or when the halt occurred.

                      Originally posted by tonata View Post
                      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?
                      The "extra cables" on your 'upgraded' 256-640KB board will be IBM's rewiring to accommodate 27256 type ROM's. Some photos in links at the bottom of [here].

                      The 05/09/86 BIOS on a 64-256KB motherboard should, at the least, start and display something. I will put the 05/09/86 BIOS into my 64-256KB motherboard, and report back.

                      Originally posted by tonata View Post
                      PB7 on 8255 shows no state. The logic probe diodes are all dark.
                      It is supposed to be high?
                      At power-on time, PB7 will be an input. Per step 5 of [here], the POST configures the pin as an output. So your measurement indicates that if (and if) the POST is running, it is not getting as far as step 5.

                      Originally posted by tonata View Post
                      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.
                      The manual for your logic probe will tell you what it displays for different things.

                      Comment


                        #12
                        Originally posted by tonata View Post
                        Can I check if the CPU is halted?
                        See post #22 at [here].

                        Comment


                          #13
                          Thanks!

                          The 3 pins 26,27,28 S0,S1,S2 are all high. So this is a HOLD state. Here it is called "passive" and it means "No Bus Cycle".
                          Ready pin is HIGH.

                          In the past there was some suspicious behavior of 8255A, but it still worked OK. Could this be explained by a defective IO chip 8255A?

                          Maybe I can measure the clocks with oscilloscope of the other chips and rule them out?

                          Comment


                            #14
                            Originally posted by modem7 View Post
                            The 05/09/86 BIOS on a 64-256KB motherboard should, at the least, start and display something. I will put the 05/09/86 BIOS into my 64-256KB motherboard, and report back.
                            I did that, and as expected, I saw a RAM count-up on the screen. So you can rule out a faulty BIOS ROM chip as the problem cause.

                            Originally posted by tonata View Post
                            In the past there was some suspicious behavior of 8255A, but it still worked OK. Could this be explained by a defective IO chip 8255A?
                            The 8255A would have to be faulty in a way that interferes with operation of the address or data buses. Quite a few chips can do that.

                            (The "suspicious behavior of 8255A" that you refer to will be what you observed during the time that we were fixing your 'keyboard port does not work' symptom. From memory, the 'suspicious behavior' was later explained by a detailed look at what the POST does with PB6 and PB7 under certain failure modes of the keyboard interface circuitry.)

                            Comment


                              #15
                              For the IBM 5160, the sequence of events that occurs before the POST starts is shown at [here]. To verify that ALL of that is happening, you would need a range of different test equipment (and the knowledge of how to use them).

                              Comment

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