3550 Expansion Unit
@E9FE.ADF - IBM Expansion Unit Model 001 
@E9FF.ADF - IBM Expansion Unit Model 002 
@8EF8.ADF - Expansion Unit SCSI Controller 
C8EF8.ADF - Init file for Expansion Unit SCSI Controller 
3550210a.exe Option Disk (v1.0): Docking Station 3550
192-258  IBM 3550 Expansion Unit Model 001
192-257  IBM 3550 Expansion Unit Model 002

Power Supply

   The -001 version is for the 8551 (N51) and the -002 version is for the 9552 (TP700/720).

System Board, Main
System Board, Sub
   J3 Pinout
Install Adapters
Open Card Retainer Catch
HD Trays

System Board, Main  FRU49G2667 (-002 model)
J1 Video pass-through
J2  P1 Power connector
J3  P2 Power connector
J4  External SCSI Connector
J5,6   Internal SCSI Connector
J8    120-Pin Connector
J9  Serial Connector
J10    System Board-Sub Connector
J11  Parallel Connector
J12  Pointing Device Connector
J13  Keyboard Connector
JP1  Password clear?
OSC1  40.0000 MHz osc
OSC2  24.0000 MHz osc
RA1-6 Termpacks
U2,25 Hitachi HM6264ALFP-10T
U3 49G2704
U5 AN78N05 VR
U7  Signetics P80C32GBAA
U9,11 89F7000
U12  39G8766
U16  48G8903
U22  53G8411 ODD SCSI BIOS

Odd configuration. The system board component side faces DOWN. The circuitboard on top is covered with a insulating shield.

Note:  The built-in SCSI controller (-002 only?) includes an active terminator. This terminator automatically works when an external SCSI device is attached.

3550 System Board, Sub
PL1  System Board-Main Interface
J3  LED and Power connectors
BT1  Backup Battery CR-2032
J1  16-bit AVE slot
J2  16-bit slot
   The edgecard goes upward into J10 on the System board. J3 points to the front of the case.

J3 Pinout
 1 Brown    +Modem
 2 Red      +FDD
 3 Orange   -FDD
 4 Yellow   -PCMCIA
 5 Green    +Charge
 6 Blue     -Speaker
 7 Purple   -Modem
 8 Grey     +HD
 9 White    -HD, -Charge
10 Black    To keylock switch
11 Red      To keylock switch
12 Red      To Power Switch
13 Black    To Power Switch
14  N/C
15  N/C

Not totally sure- the LED PCB has some bussed pins.

Installing Adapters
  You can install two full length 16 or 32 bit cards in the 3550 (but only permit 16-bit operation). Another gotcha- The slot cover guides are the same as on other microchannel systems. But the catch for the card guide is a sliding catch, not a flexible one like on the 76/77 models.

To open the catch
  Look at the vertical card guide restraint. About 2/3rds down, there is a horizontal tab. Push in on the end of the tab, then push the card guide restraint forward until it reaches the stop. To fasten it back, just slide it to the rear until the locking tab snaps into place.

Drive Tray for HDs
  When installing a 3.5" drive in a 3550 Expansion Unit, use the hard disk drive slide assembly (FRU 85F0035) supplied with the option. (Ed. a model 95 sled). The 3550 uses snap-in rail guides like those in the 77 series.

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