3550 Expansion Unit
3550210a.exe Option Disk (v1.0): Docking Station 3550
  There are two versions of this. The -001 version is for the 8551 (N51) and the -002 version is for the 9552 (TP700/720)

System Board, Main
1  External SCSI Connector
2  Serial Connector
3  Parallel Connector
4  Pointing Device Connector
5  Keyboard Connector		 6    120-Pin Connector
7    System Board-Sub Connector
8    Power Supply Connectors
9    Internal SCSI Cable Connector
10  System Board-Main Interface

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

10  System Board-Main Interface
11  Wire Assembly Connector
12  Backup Battery
13  16-Bit Expansion Slots
 
 

Backup battery looks suspiciously like a CR-2032. Backup Battery, Lithium 49G2661

Note:  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)

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