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Thread: Overview of my new Tandy Sensation II 25-1651

  1. #1
    Join Date
    Mar 2016
    Location
    Georgia, USA
    Posts
    501

    Default Overview of my new Tandy Sensation II 25-1651



    I picked up a non-working Sensation II for a good price and could not find a good set of internal photographs/teardown anywhere.

    It's a decently expandable 486SX-33 system, 5 16-bit ISA slots, supports up to 64mb RAM populated back-to-front, and has an Overdrive socket. Video chipset is Cirrus Logic 5428. Assuming mine has the factory config, which I believe it does, it came with a Soundblaster 16 1730 with a special Tandy daughtercard that integrates the on-chassis speaker and volume control with the SB16 audio mixer/output. It also has a modem installed with similar integration with the SB16 and on-board speaker.



    The case removal was straightforward. Two non-removable screws at the rear corners tighten to clamp the case to the frame. The power supply doesn't appear to actually fasten to the chassis at all, it's held in place by the metal case and slips under a metal tab in the bottom of the chassis itself. It feels secure when assembled, but gives the unit an odd flexibility if the case screws are not secured.




    The drive rails are the next piece to be removed before ISA cards can be examined. These drive bay rails/trays are interesting; they're modular, stackable trays, both identical. Each tray can hold one 3.5" drive, and one 5.25" drive, and could theoretically be stacked higher than the two units included here. Does anyone know if other Tandy or AST machines stacked more than two of these trays? Also, you need to be careful removing the top tray, mine snagged and rubbed the ground wire near the power switch quite a bit, if you're in and out of the case a lot you could damage it. There is an aluminum bay shield if your lower 5.25" bay is unused; it must be installed BEFORE the lower drive tray, and the lower drive tray needs to rest on top of the bottom lip of the aluminum spacer or your top CD-ROM drive and your case will not fit well, as you can see by the picture above.




    These are the installed drives. It looks like they are the factory hardware and seem to be in excellent operating condition. The CHS are hard to read from the photo, but are 989/12/35 just in case someone needs to know, and have to be manually entered into BIOS.



    Once the drive bays are removed you can access the ISA cards. The top card was the Soundblaster 16 1730/1740; the paper label is marked 1730, the board silkscreen is marked 1740. Maybe that means you just average the model numbers out to 1735? It has a special Tandy daughtercard that appears to use two of the SB16's connectors to redirect audio/volume controls to the front panel of the machine via a few cables.



    The second card is the modem. Not sure what speed; 1994 would have been right at the peak of 14.4kbps if memory serves me correctly. The modem is the least interesting part of the machine IMO, but I'll do a little more research on it.



    The center rail supports the ISA slot board and is held in place by a clip in the front, and a single screw attaching to the drive trays. Once you remove the screw and unclip from the front, the bar swings up and towards the back and can be removed easily. Then the ISA bus riser can be removed. Forgot to get a picture of the ISA support rail.

    The ISA slots are slightly offset from one side to another, as the ISA card bottom tabs actually overlap when installed. The left cards are slightly less recessed than the right.



    Once the drive bays, bracket, and ISA cards and riser are removed, you can see the entire motherboard.

    Some technical notes:

    System RAM needs to be installed from back to front. If not, the system posts but enters a reboot loop immediately after the first memory self-test completes.

    The on-board CPU is only usable when jumpers W6 and W7 are in the 1-2 position, and the ODP that was installed will only run in 2-3, 1-2 position respectively.

    There is a 2-pin connector from the modem, and a 5-pin connector from the front panel that were not connected in my unit. I BELIEVE they would be wired directly to the SB16 if the special Tandy daughtercard were not installed, but if anyone has any info on them I'd appreciate it.

    Full-resolution images and additional images can be found in this imgur gallery:

    https://imgur.com/a/aZL1S1n

  2. #2

    Default

    Nice looking machine. The case looks to be in very good condition, BUT do me a favor. See all those fingerprints on the metal in your photos? Try to have clean hands when handling systems plus clean off the oils from the metal that come from your paws. Over time that will oxidize. I can't tell you how many systems I restore that have decades old fingerprint oils and I can't really clean them up very well after that. Where I noticed this was in your Imgur photos.

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