77 Case, Front (40, 57 similar) Multimedia Model shown
77 Multimedia Module (Image and info from William R. Walsh)
92F0002 Control Assembly - Without Volume Control (Power Switch, Cable, Speaker)
Multimedia Module PCB (outline and info by William R. Walsh)
I would assume that the connection to the sound card powers the onboard amplifier. With the sound card cable unplugged the volume control ceases to function and the speaker plays all beeps as a normal front panel would.
MultiMedia Module PCB, Top FRU 41G3929
MultiMedia Module PCB, Bottom FRU 41G3929
92F0113 Cable (Control Assembly to Audio Card)
Those of us (un)lucky enough to have collected an Ultimedia PS/2 know that the audio features of this machine are a mix of good and bad: great front-panel amplified speaker with volume control and headphone/mic jacks, coupled to a terminally-unsupported audio card (M-ACPA or AudioVation, choose your MWAVE DSP poison). The question is: how to connect that great front-panel speaker up to a useful sound card?
As you might expect, audio is connected through a proprietary 16-pin connector that plugs into IBM's own audio cards. A few 3rd-party boards (ChipChat among them) include this "Ultimedia Header", but Creative's own SoundBlaster Pro MCV (CT-5330) does not.
But since we have the pinout, and since you can buy 2x8 dual row headers, it should be relatively easy to solder up a R/L/Gnd cable from the line out jack on the back of the SoundBlaster Pro:
(believe it or not, those pins aren't shorted :>)
Ed. pleonard connected Pins 1 (R), 2 (Gnd), and 10 (L). But the wiring doesn't quite match the pinout! Yet it supposedly worked for him... hmm. Needs verification.
As you'd expect, best results are obtained by disabling the built-in amp on the SBPro. The result is very clean sound - contemporary (1991) reviews of the Ultimedia mention how these machines' own sound hardware obviated the need for external speakers for most users. Best of all, you can completely uninstall the original DSP sound card. (Your sympathies for the original IBM sound card will dramatically decrease when you discover how many dozens of KB of RAM it requires to produce sound of any kind in DOS...!)
77 Case, rear (57SX shown)
77 5.25" Drive Bay Guides
Post Notches on the reverse that fit into
the drive bay walls.
To remove Guides
Press in the latch on the guide (rear of the drive bay) and push the guide forward.
These are mirror images of each other, one for the left side, the other for the right side. If you make your own guide rails, you can cut the back end of the rail square, so it wouldn't matter if you used the same FRU on both sides The cutout for the gude's latches will allow you to switch the guides to the other side and they will work.
96F7371 (Black) Left Guide
Original 77 5.25" Drive Rail
This was "fun". On this rail, the screw hole marked "R" was the fixed hole, and it serves as the reference point for the important surfaces. Note that the center-to-center distance is 3.115". Measured that from a drive. One hole is usually slotted so there can be some variation between mounting screw locations on drives.
Also, with any measurement, a few thousandths here and there doesn't matter.
5.25" 77 Drive Rail Hack
Get the ubiquitous 5.25" AT Drive Rail. Cut
to fit. Note the web sticking down at the end of the
guide (.469"). This web has two functions - first,
limiting the 5.25" device to the proper depth. Second,
it prevents upside-down installation of a drive if you
use the original drive rails with the matching
extensions that fit the .469" rear.
Fixed Disk Bay 4C Drive Slide 96F7775, 71G5706, 71G5708, 79F3300
Seems this is a little long for OAL for it to fit into the Model 90's lower drive bay.
9577 Air Baffle for Fixed Disk Bay 4C FRU 92F0251
The older 8557 and 9557 used a grey colored baffle, same FRU.
This was used in older systems with hot running drives in 4C. Modern 1" high drives should run cool enough without it, but if you want to run a 7,200RPM (or higher) drive in your 77, you MIGHT want to help cool it as much as possible.
I built a baffle for a 9577 that went from the top air grill on the power supply over to the D: drive bay above the control module. Worked fine. A little duct tape, some pasteboard, and shazzam! I don't have a 77 anymore to give you dimensions.