8525B/8528 Technical Service Manual Technical Description 4-3
Publication No: 15-02036 Issue 6
Pressing the power on/off pad with relay K2 set to ‘on’ has no effect on V2
on the Motherboard. However, via the front panel I
2
C bus control, the
microprocessor grounds the Power Off line, J3 pin 5. This energises the ‘off’
coil of K2, toggling the relay back to its ‘off’ state. Contacts of K2 open to
break the energising path for relay K7 on the PA and filter PCB.
4.1.5 High Power Transceiver Protection and Power On/Off
In place of the PA and Filter PCB, transceivers fitted for external PA
operation have a PA/Exciter Interface PCB (08-03691). This does not
contain overvoltage and reverse voltage protection circuits. In these
transceivers the power supply is connected to the PA unit where reverse
voltage protection is provided. Operation of the on/off pad on the transceiver
grounds a line which is taken, via the PA Exciter Interface, to the PA unit.
This energises relays in the unit which in addition to switching power on to
the unit, also switch the supply back to the transceiver. The supply to the
transceiver is taken, via the PA/Exciter Interface, to energise relay K2 and
switch on the transceiver in the normal way.
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