Service manual

Protection Circuit for Bridge-Coil and Frame Output Stage
The secondary voltage of bridge coil L5422 is guarded at the diode modulator
(D6421/22) via a detection circuit consisting of an 8.2 V zener diode (6499 on diagram
A3). When the bridge-coil is working properly, the average voltage on D6422 is such
that this zener diode will conduct and will drive TS7652 into saturation via the
BRIDGE_PROT signal (see diagram A4). When, for any reason, the secondary side of
the bridge-coil is shorted, the average voltage on D6422 will drop below the zener-
voltage and TS7652 will block. Now capacitor C2642 will be charged. Transistor
TS7407 will start conducting and the DEFL-PROT (= STANDBY, see diagram A3)
signal will be grounded via R3403. This will switch off the main supply (see diagram
A1).
Via the circuit built around TS7641 the frame output stage is guarded. If the frame
output stage is working properly, TS7641 and TS7652 will both conduct and thereby
discharging C2642. TS7407 is blocked now, causing the DEFL-PROT signal to have a
high resistance.
If there are frame pulses missing, TS7641 will block and capacitor C2642 can be
charged. Transistor TS7407 will now start conducting and the STANDBY (=DEFL-
PROT) signal will be grounded via R3403. This will switch off the main supply (see
diagram A1).
Audio (Diagram B6, A5 and A6)
Introduction
All N8 sets contain one of ITT's Multistandard Sound Processing ICs for sound
decoding. The USA-version uses the MSP3451G (Global decoding and Virtual Dolby).
This IC takes care of the main FM sound decoding.