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Thread: Sensation II, great physical condition, not posting

  1. #1
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    Default Sensation II, great physical condition, not posting

    I've picked up a Sensation II in excellent physical condition, basically looks brand new on the inside and very good on outside.

    Has a DX2/66 overdrive installed, what looks like 8mb of memory, and the factory hard drive/expansion cards.

    The problem is that there is no POST at all when I apply power. The CD-ROM and hard drive power up and self-test, there is no beep or floppy seek.

    I verified that the PSU is supplying 5v and 12v (and -5v). I uninstalled all expansion cards and ribbon connectors. I've tried switching back to the on-board CPU (from the Overdrive processor).

    I have packed away all my ISA VGA cards, but disabling on-board VGA didn't change behaviour at all.

    Some fairly high-quality photos of the motherboard with all cards removed is at https://imgur.com/a/XtY53jq I see nothing that looks remotely suspicious here.

    I've verified that the voltages supplied to the ISA slots and to the BIOS are correct. The BIOS is an EPROM, possibly it has been corrupted, I pulled the chip and dumped the ROM images, they are attached below.

    I just moved, so once I find my NICE multimeter I'll see if the ISA CLK signal is correct, but my guess is that something is wrong with BIOS. I should be able to use the rudimentary bios CHECKSUM algorithm to verify there's no corruption, right?
    Attached Files Attached Files

  2. #2
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    I swapped the Tandy Sensation BIOS with a generic AMI486 bios file in PCEM, and it boots to "Press F2 to enter setup utility", so I don't think the bios itself is too corrupted or unable to post.

  3. #3
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    I also overwrote the PCEM CL5429 bios with the CL5428 bios from the Tandy .bin and it also boots to setup prompt, so I no longer think it's a ROM corruption issue.

  4. #4
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    Quote Originally Posted by keenerb View Post
    I also overwrote the PCEM CL5429 bios with the CL5428 bios from the Tandy .bin and it also boots to setup prompt, so I no longer think it's a ROM corruption issue.
    I noticed the W6 and W7 jumpers are both in 2-3 position, but the screenprinted designations are confusing. Since the on-board cpu is a 486SX, I'd expect the DEFAULT position to support the 486SX.

    And what's up with W7 having a setting for DX/DX2/SX and a setting for DEFAULT? DX/DX2/SX would be the only possibly combinations for the upgrade socket.

    Also, I believe the installed CPU isn't even an overdrive chip, I think it's a standard DX2/66 as it's missing the extra pin; will that even work in this system?

  5. #5

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    Motherboard jumpers: https://stason.org/TULARC/pc/motherb...DEL-10-20.html

    and ftp://ftp.oldskool.org/pub/tvdog/tan...back/02744.pdf

    Radio Shack used to have a nice support site with all the info, but......

  6. #6
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    Quote Originally Posted by njroadfan View Post
    Motherboard jumpers: https://stason.org/TULARC/pc/motherb...DEL-10-20.html

    and ftp://ftp.oldskool.org/pub/tvdog/tan...back/02744.pdf

    Radio Shack used to have a nice support site with all the info, but......
    Interestingly enough, the faxback doc seems to contradict stason.org.

    The faxback seems to tell me that, for a ODP 66MHZ I need W6 1-2, W7 2-3, stason says W6 1-2, W7 1-2.

    The photo I just found at https://parasomia.files.wordpress.co.../img_14904.jpg shows W6 1-2, W7 2-3, with an overdrive DX4 processor installed, and he boots his machine and plays some games.

    That will be a nice surprise, as shipped the jumpers were in 1-2, 1-2 and non-functional. If switching W7 to 2-3 works I'll be pleasantly surprised.

  7. #7
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    Quote Originally Posted by keenerb View Post
    Interestingly enough, the faxback doc seems to contradict stason.org.

    The faxback seems to tell me that, for a ODP 66MHZ I need W6 1-2, W7 2-3, stason says W6 1-2, W7 1-2.

    The photo I just found at https://parasomia.files.wordpress.co.../img_14904.jpg shows W6 1-2, W7 2-3, with an overdrive DX4 processor installed, and he boots his machine and plays some games.

    That will be a nice surprise, as shipped the jumpers were in 1-2, 1-2 and non-functional. If switching W7 to 2-3 works I'll be pleasantly surprised.
    Boots with 1-2, 2-3 jumper configuration. Drops into a reboot loop immediately after posting. It seems the SIMMS must be populated back to first to have a successful boot, the slots closest to the front of the case will allow system to boot but immediately cause a loop. It was only when I finally placed the SIMM into the very back that the system would boot normally.

    It seems to be working fine now!

    IMG_20190109_174414579.jpg
    Last edited by keenerb; January 9th, 2019 at 02:59 PM.

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