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This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

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A few 5150 questions:

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    A few 5150 questions:

    Hi everyone,

    I fairly recently picked up two IBM 5150s in rather dirty and sad shape and I've been restoring them this month. Both systems are cleaned up and power on (256 rev mobo with the last bios), but one of them has a few issues I'd like some advice on so I don't damage the system and can get it in fully working order.

    Firstly, it had a parity ram issue that after much research (thank you minus zero degrees) I narrowed down to the parity bit on bank 0. I have a few spare 4164 ram chips and placing one on top of the chip resolved my error. Unfortunately, bank 0 is the only non-socketed bank. I don't have much experience desoldering on these old boards and the last thing I want to do is lift any traces or similiar trying to remove this bad chip. Would simply soldering a spare on top of the existing chip be a bad idea? Any general tips for not damaging these boards would also be appreciated.

    Secondly, one of the floppy drives is just broken. I can't even test if the stepper works because the head of the drive has physically broken off and fallen down into the mechanism and it doesn't seem fixable. How hard is it to source a working full height replacement for these floppy drives? Is it possible to just get the head assembly? I'll attach a photo of how it's broken.

    Apart from those issues, it's a great computer and cleaned up very well, so I'm hoping that my "parts" machine can return to being a second fully working 5150 with minimal effort. I'll also include some general photos of the IBMs as well just so you can get a good look at the systems. I do know to park the MFM hard drive on the model with one equipped, but I haven't worked much with these early IBMs so any tips and tricks are much appreciated.Thanks!

    broken_fdd.jpg
    IBM1.jpg


    ibm2.jpg
    Attached Files

    #2
    Originally posted by username1 View Post
    I have a few spare 4164 ram chips and placing one on top of the chip resolved my error. Unfortunately, bank 0 is the only non-socketed bank. I don't have much experience desoldering on these old boards and the last thing I want to do is lift any traces or similar trying to remove this bad chip. Would simply soldering a spare on top of the existing chip be a bad idea?
    The only situation that I can think of where it might be bad, is where the piggybacked chip is intermittent.

    Originally posted by username1 View Post
    Any general tips for not damaging these boards would also be appreciated.
    For removing faulty chips, I wrote up my technique at [here].

    Originally posted by username1 View Post
    Is it possible to just get the head assembly?
    The assembly that slides on the rails. It is possible, but after replacement, a 'radial head alignment' will be required. See the 'Incorrect head alignment' section of [here].

    Comment


      #3
      Originally posted by username1 View Post
      I don't have much experience desoldering on these old boards and the last thing I want to do is lift any traces or similiar trying to remove this bad chip. Would simply soldering a spare on top of the existing chip be a bad idea? Any general tips for not damaging these boards would also be appreciated.
      I've found modem7's technique to work well, even though I only have a copper desoldering braid. Getting the GND and VCC pins out takes a tremendous amount of heat on the 5150 board but all the other pins come right out. I haven't even needed to add solder first. I don't obsess over getting every last bit of solder out, since I'll just be putting in an IC socket.

      You can actually combine that idea with 'piggybacking': remove the bad IC leaving just the legs, and then piggyback the new IC onto the old legs. I do this sometimes when testing.

      Comment


        #4
        You can actually combine that idea with 'piggybacking': remove the bad IC leaving just the legs, and then piggyback the new IC onto the old legs. I do this sometimes when testing.
        This sounds like it's probably the best option unless username1 is already experienced with soldering. As someone with only minimal soldering skills I found my first desoldering experience to be a fairly intimidating challenge, especially since I was worried about applying too much heat and frying something.

        Comment


          #5
          Originally posted by modem7 View Post
          The only situation that I can think of where it might be bad, is where the piggybacked chip is intermittent.
          Note that readers should not take my statement out of context of the OP's particular situation. There are cases of chip failures where simply soldering a good chip over a bad chip will not work. Example at [here].


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