FECO 3000 # 29

Note: full ESD precautions must be used when handling PCB's

1. Change The SCSI differential daughter board has been introduced. It attaches to a 53c710 pxa PCB to enable a differential external interface. On an NCR3430 it can plug directly into the system board.
   
   
2. Identity The mecc identity is: NCR 3 - 53c710 (pxa)(dif-daght) (tech serv ref 15/8/1)
   
   
3. Installation The kit includes the daughter PCB and two nylon stand offs. To install the daughter board on a SCSI host adaptor board, insert the two nylon stand offs (included in this kit) into the stand off holes on the daughter board. Then, align the pga header (p1) on the daughter board with the pga socket on the host adapter board so that the extra pin on the header is above the extra pin on the socket. Lower the daughter board into the socket ensuring that the nylon stand offs are aligned with the stand off holes on the host adapter board. Refer to the following illustration to ensure proper board installation.
   
   
4. Servicing

there are no preventive maintenance routines associated with the SCSI differential daughter board, and it contains no user-set switches or adjustments. Any initial errors will be noted by the computer at start-up, and the board should then be reconfigured using the reference/bios diskette. If reconfiguration is not successful, a critical failure has occurred which prohibits further use of the board and requires that the entire board be replaced. Complete the steps below to service the SCSI differential daughter board. verify that the SCSI differential daughter board is installed correctly and that there are no damaged pins. The pga socket and the pga header are keyed to ensure proper installation. If any pins are damaged, replace the board. ensure that no single-ended devices are attached either internally or externally. The SCSI differential daughter board only functions properly with SCSI devices that support a differential bus implementation. if external SCSI devices are attached, ensure that all external cables, connectors, and jacks are properly connected and in good condition. In addition, ensure that all external SCSI devices are correctly daisy-chained, are connected and terminated properly, and have the proper SCSI ID jumper or switch settings. Refer to your computer user guide for additional information on SCSI devices. if no external SCSI devices are attached, ensure that SCSI terminating resistor packs are installed in RP1, RP2, and RP3 or a SCSI terminator plug is connected to the external SCSI connector J5 on the SCSI differential daughter board. if no internal SCSI devices are attached, ensure that SCSI terminating resistor packs are installed in RP1, RP2 and RP3. check fuse f1 on the SCSI differential daughter board. If this fuse is blown, termination power (termpwr) is inadequate, and erratic operation of any or all attached SCSI devices is probable. If f1 is blown, replace the board. Refer to the "para 6" for additional information on termpwr. if steps 4.2 to 4.7 do not correct the problem, replace the boar

5. Features The SCSI differential daughter board provides an additional SCSI channel through a 53c710 SCSI i/o processor. The SCSI differential daughter board also has the following features.
   
   
6. supports a fast SCSI-2 bus (10 mb/s transfer rate).
   
   
7. supports up to seven additional SCSI devices connected internally or externally in daisy-chained configurations.
   
   
8. provides an 8-bit, differential SCSI bus implementation.
   
   
9. provides pluggable on-board, differential termination.
   
   
10. supports a maximum cumulative cable length of up to 25 metres.
    
    
11. SCSI termination and termination power circuitry The SCSI differential daughter board supports socketed SCSI bus termination that can be installed or removed based on the specific SCSI application. For applications requiring connectivity of internal-only SCSI devices or external-only SCSI devices, the terminating resistor packs (rp1-rp3) must be installed to establish SCSI bus termination at the daughter board end of the bus. For applications requiring connectivity of internal and external SCSI devices to the daughter board, the terminating resistor packs (rp1-rp3) must be removed, and termination must be provided through another means at the last internal and last external SCSI device position (ends of the bus). The SCSI differential daughter board is designed to provide termination power (termpwr) to the SCSI bus. Termpwr is supplied to both the internal and external SCSI connectors through a 1.5 a fuse (f1) and a schottky back-flow protection diode. Since the daughter boards supplies termpwr, no other SCSI device connected to the board should supply termpwr to the bus.
    
    
12. PGA Header (p1) The SCSI differential daughter board provides a pga male connector to interface the daughter board and a SCSI hose adapter, or to interface the daughter board and the computer baseboard.
    
    
13. Pin and plug assignments

the SCSI differential daughter board provides for an internal and external interface connection through two distinct connectors. Internal SCSI devices interface to a 50-pin position header (center polarized) that connects directly to the internal SCSI data cable. External SCSI devices interface to a 50-pin d-shell connector. Both connectors are signal-for-signal identical, but they are not pin-for-pin identical. internal SCSI connector (J4). A 50-pin, ejector-ear connector interfaces with a standard ribbon connector on the internal SCSI data cable to transmit signals between the SCSI differential daughter board and internal SCSI i/o devices. The cable must be rated at 100 ohms impedance (+ or - 10 ohms) or greater. external SCSI connector (J5). A 50-pin, miniature d-shell connector transmits signals between the SCSI controller and external SCSI devices.

14. Testing No special testing procedure.
    
    
15. recording action No specific recording action.

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