9914V TAPE UNIT

2.PCB DescriptionsThis section contains functional descriptions of the major pcbs. Fault-finding techniquesare described in Section 3.The circuit deSCriptions are related to signal activity when in operation, and enable faulttracing to the signal source I destination on the board (having first used the diagnosticprograms to identify the suspect area). Having established that the board is interfacingcorrectly, the next stage will normally consist of board substitution. On-site diagnosis downto chip level is not anticipated, partty because extensive use is made of surface-mountcomponents, and partly because down-time is reduced by sub-assembly substitution.2.1 Care of Printed Circuit BoardsRepair or modification of the surface-mount components shouid not be attempted withoutsuitable surface-mount rework facilities.CautionAll the boards described here include CMOS integrated circuitsand I or CMOS components, for this reason the usual static precautionsshould be observed when handling them.2.2 Servo Control Board Description2.2.1 OverviewThe Servo Control board, part number 125370, contains the following functions:a) Interface circuits:i) to register signals from the operator panel, for interpretation by the microprocessor,ii) to transfer indications to the operator's 8-charader alpha-numeric front panel display;iii) to communicate with the Data Control board, controlling tape motion which corresponds tothe last accepted command (from the host or operator);iv) to drive the hub lock mechanism;v) to drive the loading fan.b) Analogue circuits:i) to process the tape speed data (ie the processed tacho output pulses) and complete thecontrol loop by deriving the take-up motor drive current;ii) to process the tape position data and derive the offset value which is applied to the supplymotor current, thereby compensating for the varying radius of the tape stack.95 125456 (Draft Issue D) PCB Descriptions 2 - 1