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Thread: PS/2 Model 76 keeps locking up

  1. #1
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    Default PS/2 Model 76 keeps locking up

    Hello,

    So I just bought an IBM PS/2 Model 76 from eBay. The hard drive in it was bad and the seller was up front and honest about it so pretty much the first thing I did when I got it was order a new hard drive (IBM 2GB SCSI). Got it formatted and got PC DOS 6.3 installed and I find it just keeps locking up on me. The computer is totally unresponsive (even to ctrl+alt+del) until I do a hard reboot.

    I first noticed it after I installed DOS so I thought the OS was the problem. I tried reformatting and installing PC-DOS again (version 6.1), I also had an MS-DOS 6.22 boot disk handy and that eventually locked up too. I then thought it could be because I didn't have my XGA drivers installed. So installed them and that didn't fix it.

    When I was waiting for the new hard drive to arrive I was messing around playing games off a Windows ME boot disk and never had a problem so it might be the drive. Old SCSI drives aren't known for their reliability.

    I'm hoping it's not a hardware issue as parts for these things are hard to come by. I'm noticing that the more I use it the faster it locks up after boot so maybe it's heat related?

    Anybody seen this before or have any tips for troubleshooting?

    Thanks in advance!

  2. #2

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    I recently had this exact issue, turned out the SCSI controller based on an NCR chip, was not supplying termination power. Setting the drive to supply the term power solved the issue. Of course your problem may be something else, but its worth a check. My system locked up when writing to the disk.
    Looking for: OMTI SMS Scientific Micro Systems 8610 or 8627 ESDI ISA drive controller, May also be branded Core HC, Please PM me if you want to part with one.

  3. #3
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    Quote Originally Posted by mR_Slug View Post
    I recently had this exact issue, turned out the SCSI controller based on an NCR chip, was not supplying termination power. Setting the drive to supply the term power solved the issue. Of course your problem may be something else, but its worth a check. My system locked up when writing to the disk.
    Thanks for the reply.

    I have the termination jumper on (Pin 6 - SCSI Term On). Does that supply termination power? I can't find another jumper that seems relevant.

    EDIT: Should probably have mentioned that the drive model is an IBM DORS-32160 http://ps-2.kev009.com/ohlandl/IBM_HD/dors_ps.pdf
    Attached Images Attached Images
    Last edited by sa230e; June 21st, 2018 at 07:22 AM. Reason: Adding drive model

  4. #4

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    Well, it seems like your drive doesn't have that functionality. Many newer drives don't. The drive mentions active-termination, so I'll assume by the time active-termination came along, the SCSI controller provides the power. But I don't know for sure.

    I think my 77 with the Bermuda Planner doesn't have much issue with SCSI, though I have only a ~200MB drive in there IIRC. Are there resistor packs installed at ST1 and ST2 on the motherboard?
    http://ps-2.kev009.com/ohlandl/76-77/7677_Bermuda.html
    Looking for: OMTI SMS Scientific Micro Systems 8610 or 8627 ESDI ISA drive controller, May also be branded Core HC, Please PM me if you want to part with one.

  5. #5
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    Quote Originally Posted by mR_Slug View Post
    Well, it seems like your drive doesn't have that functionality. Many newer drives don't. The drive mentions active-termination, so I'll assume by the time active-termination came along, the SCSI controller provides the power. But I don't know for sure.

    I think my 77 with the Bermuda Planner doesn't have much issue with SCSI, though I have only a ~200MB drive in there IIRC. Are there resistor packs installed at ST1 and ST2 on the motherboard?
    http://ps-2.kev009.com/ohlandl/76-77/7677_Bermuda.html
    Sure looks like it.

    20180623_183458.jpg

  6. #6
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    So I had a little more time to play around with it today and I took to the hard drive out completely and just booted off a boot disk and sure enough it locked up. So the hard drive's not the problem.

    So I did what I would with a modern PC and started reseating components. I reseated the XGA2 card and the RAM (a single 8MB SIMM). I ended up actually moving the RAM to slot J9 because it was the easiest to access (it was in slot J11 when I got it). I took out the token ring NIC entirely because I'm never going to use it. It's still locking up.

    If this were a modern PC, I would swap out the PSU next but I doubt I'll find another PSU for a model 76 any time soon. I do have a PSU tester but it has an ATX connector. It also has a molex connector though so I can at least test 12v and 5v and they seem fine.

    I suspect heat is a problem with these PCs. There's not very much for airflow in there at all. Both the onboard CPU and the XGA2 card get fairly toasty - and that's with the cover off.

  7. #7
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    Anybody have any advice?

  8. #8

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    Could be one of many things. Unless you are skilled and have the time + tools to troubleshoot in detail (to MOBO & PSU component level) waiting for a parts machine to pop up and restoring one of them that way is the only option.

    Also ask the IBM PS/2 newsgroup: there are diehards there.

  9. #9

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    Quote Originally Posted by sa230e View Post
    I suspect heat is a problem with these PCs.
    I seriously doubt heat is the cause here.

    Heat takes some time to build up and cause problems. If you're turning the machine on and it's locking up immediately you need to look elsewhere for the cause.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  10. #10
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    So when I first got the computer before I got the replacement hard drive I was just booting of a DOS boot disk I made with my old Windows XP machine (if you run ver it identifies as Windows Millenium) so I tried that again and it was stable for a good 2.5 hours but it did end up locking up too. Compare that to PC-DOS 6.3 which would lock after maybe 10 minutes or an MS-DOS 6.22 boot disk which got me maybe 15 minutes. The version of DOS seems to matter.

    On the hardware side, according to this (http://john.ccac.rwth-aachen.de:8000/alf/ps2_76/) the CPU can be upgraded to a 486 DX2 66 which I was planning to do anyway so I ordered one. If it's the CPU that's bad, this should fix it. I also am looking at ordering some RAM to test with as well.

    If neither of those work I plan to recap the PSU.

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