Overview of my new Tandy Sensation II 25-1651

Discussion about old PC hardware.

Overview of my new Tandy Sensation II 25-1651

Postby keenerb » 2019-1-10 @ 14:33

Image

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.

Image

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.

ImageImageImage
Image

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.

Image
Image

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.

ImageImageImage

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.

Image

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.

Image

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.

Image

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
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby chinny22 » 2019-1-10 @ 16:17

Nice looking 486 and that daughterboard is pretty special
Did you get it working in the end?
User avatar
chinny22
l33t
 
Posts: 2307
Joined: 2011-8-26 @ 12:02
Location: Australian but living in the UK for now

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

Postby keenerb » 2019-1-10 @ 16:19

Yeah played some Duke Nukem 3D on it last night. Runs like a champ! The CPU jumpers were set incorrectly.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby TheMobRules » 2019-1-10 @ 16:46

Very nice machine! It has that classic "early multimedia PC" look!

I assume the onboard Cirrus Logic VGA runs on some kind of local bus rather than ISA?
TheMobRules
Member
 
Posts: 438
Joined: 2016-1-19 @ 23:29

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

Postby keenerb » 2019-1-10 @ 17:00

That's a good question; I have no idea if it's VLB or not.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby Ozzuneoj » 2019-1-10 @ 17:20

Very cool system! The Sb16 daughtercard is interesting.

Forgive my lack of knowledge on this subject, but what is the back story behind these? I can't find much information about Tandy branded computers past the 1000. I had a 1000HX back in the early 90s so I'm curious.
Time Machine = FIC PA-2013 2.1 - K6-2 500 - 256MB PC-100 - TNT2 Pro 16MB AGP - Labway Yamaha YMF719-E - Midiman MM401
Amibay For Sale Threads
I have lots of PC stuff for sale on Mercari! Get $10 off your first purchase with my invite link!
User avatar
Ozzuneoj
Oldbie
 
Posts: 1530
Joined: 2016-3-16 @ 21:33

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

Postby DaveJustDave » 2019-1-10 @ 17:34

Good work! I had read somewhere that some sensations had sound hardware that was essentially an adlib gold clone? can someone chime in?

I had no idea these systems came with an overdrive socket! what an excellent find!
I have no clue what I'm doing! If you want to watch me fumble through all my retro projects, you can watch here: https://www.youtube.com/user/MrDavejustdave
User avatar
DaveJustDave
Member
 
Posts: 231
Joined: 2013-10-03 @ 04:00

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

Postby keenerb » 2019-1-10 @ 17:49

Ozzuneoj wrote:Very cool system! The Sb16 daughtercard is interesting.

Forgive my lack of knowledge on this subject, but what is the back story behind these? I can't find much information about Tandy branded computers past the 1000. I had a 1000HX back in the early 90s so I'm curious.


Tandy made a number of systems in the 386-486 class in the early 90's. Most were rebranded AST systems. I believe the Sensation II is the very last Tandy-branded computer to hit the market, but I'm not positive; after this machine everything was sold to AST.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby keenerb » 2019-1-10 @ 17:50

DaveJustDave wrote:Good work! I had read somewhere that some sensations had sound hardware that was essentially an adlib gold clone? can someone chime in?

I had no idea these systems came with an overdrive socket! what an excellent find!


The Sensation I (25-1650) was the machine with the adlib gold-quality audio and Tandy DAC. This is the followup, which relied on Soundblaster 16 cards for audio.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby NJRoadfan » 2019-1-10 @ 20:00

Quick note: The model number is actually 250-1651, Tandy tended to strip out the zero from their model numbers for some reason. I think that modem has some voice capability (the wiring loops thru the PC Speaker audio to the sound card). The daughtercard on the soundcard has several functions. It mixes the PC speaker/modem's outputs with the main soundcard output and also supports the volume control on the front of the machine. It also routes audio to the internal speaker and the mic/headphone jacks (looks like there is an audio amp in the mix as well).
NJRoadfan
Oldbie
 
Posts: 948
Joined: 2012-5-26 @ 03:54
Location: Northern NJ

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

Postby keenerb » 2019-1-10 @ 20:15

I have seen reference to the Sensation II having a fairly advanced voice-mail system, which may be what the audio routing from modem is used for. I can't imagine much else you'd do with SB16 - modem connections.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24

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

Postby 9646gt » 2019-1-11 @ 03:27

I want to run across one of those so bad. That is THE computer that got me into computers when I was in 5th grade and used it at school every chance I got!
9646gt
Newbie
 
Posts: 51
Joined: 2018-12-14 @ 13:55

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

Postby matze79 » 2019-1-11 @ 20:43

Does it also support 3 Voice Sound and Tandy DAC ?
the SB16 Daughterboard seems only to have a LM386 Amp and some logic..
https://dosreloaded.de - The German Retro DOS PC Community
https://www.retroianer.de
matze79
Oldbie
 
Posts: 1413
Joined: 2014-12-12 @ 14:25
Location: Germany, Frankonia

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

Postby keenerb » 2019-1-11 @ 20:47

No, it doesn't have the PSSJ/Tandy DAC. Just Soundblaster for audio. It's really a fairly generic 486 system under the hood IMO.
keenerb
Oldbie
 
Posts: 763
Joined: 2006-11-13 @ 16:24


Return to General Old Hardware

Who is online

Users browsing this forum: happycube, jheronimus, The Serpent Rider, undeon and 8 guests