60 Circuit Descriptions TB7100 Service Manual
© Tait Electronics Limited October 2005
ESD Protection
On exposed inputs of the auxiliary and control-head connectors ESD
(electrostatic discharge) protection is provided by a 470pF capacitor and by
clamping diodes to ground and to 13.8V. For example, on
AUX GPIO4 this
would consist of D713 and C725. The lines
IOP GPIO1 to IOP GPIO7 are
intended for connection to internal digital devices and so these have
relatively light protection.
Hookswitch
Detection
Hookswitch detection is performed by Q700, R709, R706 and R712.
When the resistance to ground on the PTT line is less than 13.2kΩ, Q700
will turn on and drive the
ITF CH HOOK line high; this indicates either that the
microphone is on hook or that the PTT (press-to-talk) switch is pressed.
4.8 Digital Board
Introduction For a block diagram of the digital board, refer to Figure 4.8.
The digital board is not serviceable at level-2 and is not described in this
manual.
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