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Thread: IBM PC 5150 stubborn POST 601 error

  1. #1

    Default IBM PC 5150 stubborn POST 601 error

    Hello guys,

    My name is Philippe and I am trying to get an IBM 5150 to work.
    The machine is a 2nd revision of the motherboard and has the 3rd revision of the bios.
    The machine powers on and shows the 601 POST error (floppy error) then it loads basic and basically the PC works great in basic but i'd like it to be more useful than just basic

    What I did so far:
    1. I checked the switches on the motherboard to check that the correct number of drives was selected. (switches ok)
    2. I checked the cable to the floppy drives, the correct connector connected to the correct drive and the terminator dip package on the last drive on the cable. (so cable connections ok)
    3. I swapped the controller card. (no success)
    4. I tested both disk drives in a 386 and they work perfect on the 386, I was able to read and write to the floppy drives. (so drives are ok)
    5. I used the power cables of the IBM PC but left the floppy drives data cables connected to the 386 -> they still work work fine (so power is ok)
    6. I acquired an XT clone and I replaced the controller card with the controller card and data cable of my IBM PC and the disk drives work fine in the XT clone (Meaning that the controller and cable are also ok)
    7. I tried to place the controller card in every single ISA slot the PC has. ( no success)
    8. I tested with only 1 drive and changed the switches on the motherboard to indicate I only have 1 drive and tested this with both drives putting the terminator dip package on the drive that was connected but no success.
    9. I tried with floppy drives from the XT computer but no success.

    so as a summary:
    floppy drives tested and ok
    power tested and ok
    data cable tested and ok
    controller card tested and ok
    terminator checked and ok
    motherboard switches checked and ok
    ISA slots seem to be ok (They work for my VGA and MDA card)

    -> still 601 error in my IBM 5150

    I'm completely out of ideas now.. I hope someone here has seen this before and can give me a clue where to look next.

  2. #2
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    1. On an IBM 5150, about 50 seconds or so after power-on, expected to be observed is the A: drive's disk access LED turn on momentarily, the drive's spindle turn, and the drive's heads moving out to track 34. Seeing any/all of those ?

    2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)

  3. #3

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    Quote Originally Posted by modem7 View Post
    1. On an IBM 5150, about 50 seconds or so after power-on, expected to be observed is the A: drive's disk access LED turn on momentarily, the drive's spindle turn, and the drive's heads moving out to track 34. Seeing any/all of those ?
    With the controller card in the 5150 no
    With the controller card and floppy drives an XT clone yes.

    Quote Originally Posted by modem7 View Post
    2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)
    I didn't check with a multimeter but I thought I ruled that out by powering the floppy drives from the 5150's power supply while having the data cable connected to my 386. (and that worked I could use the drives in the 386 while powered from the 5150 PSU.)
    I believe I even did the test the other way around too. powering the drives from the 386 and the data cables to the 5150. (with the same 601 error as a result but it's been some time since I tested this so it can be my imagination)
    So I was quiet sure back than it had to be the controller card. (so I bought a spare one online which was promised to be working, but I got the same error with the spare card)
    Only last weekend I found an XT clone and thought that was perfect to test the controller card. I was annoyed to found out that the controller card worked in the XT clone.... so that rules out that the controller card has an issue I believe.
    Anyway I will take your advise and measure with a multimeter just to be sure.

  4. #4
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    The floppy controller relies on two devices for successful operation--the 8259 interrupt controller (IRQ 6) and the 8237 DMA (DMA channel 2) controller. It could well be possible that there's a discontinuity or fault between the ISA bus and either of these devices. An oscilloscope or logic analyzer might pick up the problem.

    It's also possible that the address decoding for the ISA bus isn't working. That can be checked from BASIC.

  5. #5
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    Quote Originally Posted by philippe_d View Post
    Anyway I will take your advise and measure with a multimeter just to be sure.
    Yes, just to be sure.

    In addition to what Chuck wrote, you could try a Supersoft/Landmark diagnostic ROM (via adapter) in motherboard socket U33.
    It may show a motherboard problem, pointing out the problem area.

  6. #6
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    Under BASIC, try the following:

    Code:
    OUT &H3F2,&H1D
    The LED on drive A: should go on and the motor should start spinning.

    Code:
    PRINT INP(&H3F4)
    You should get 128. This will at least verify that your card is seen by the system.

  7. #7

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    Thanks guys these are very useful replies.

    I'll measure the voltage on the floppy drives for +12v and I'll try the basic commands from Chuck to verify if the controller card can be seen by the system.
    I don't have an oscilloscope so I hope I'll not need one of those..
    That diagnostics rom will also need to wait for now, I don't have one so I'll need to get me an eprom programmer or I see there are some people that can program one for me: http://www.minuszerodegrees.net/rom/...g_services.htm

  8. #8

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    The really early IBM floppy controller with tin cans also use -5V if I am not mistaken. That's also something to check.

    You might also try a general purpose Floppy-controller in the XT. Doesn't matter if it's on a multifunction card that's 16-bit, as most later FDC chipsets only use the 8-bit portion of the ISA bus.
    Current systems owned by me:
    Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
    Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

  9. #9

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    Quote Originally Posted by Chuck(G) View Post
    Under BASIC, try the following:

    Code:
    OUT &H3F2,&H1D
    The LED on drive A: should go on and the motor should start spinning.
    No success... not a single sign of life...

    Quote Originally Posted by Chuck(G) View Post
    Code:
    PRINT INP(&H3F4)
    You should get 128. This will at least verify that your card is seen by the system.
    No success... I get 0 back

    Quote Originally Posted by modem7 View Post

    2. Using a multimeter, verify that +12V is being generated. (In your 5150's configuration, the floppy drive will be only thing using +12V.)
    I measure +12.11V on the output of the PSY going into the drives. (and 5.12V on the other wire)

  10. #10

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    Quote Originally Posted by per View Post
    The really early IBM floppy controller with tin cans also use -5V if I am not mistaken. That's also something to check.

    You might also try a general purpose Floppy-controller in the XT. Doesn't matter if it's on a multifunction card that's 16-bit, as most later FDC chipsets only use the 8-bit portion of the ISA bus.
    It is this one : http://minuszerodegrees.net/5150/ear..._3996x2054.jpg

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