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POWER BOARD
Faults:
+DC at the output:
Via D6287 a positive voltage arrives at the base of TS7287, causing the collector of TS7287
to become LOW. TS7280 blocks. Via the potential divider R3279/R3281 a voltage of approx.
1V presents itself at R3281. The result is that a voltage of approx. 0.7V lies on the base of
7S7279 and the emitter of TS7282 respectively. The transistors switch through and thus
block TS7278 and 7283. The voltages +STBY and -STBY are not switched through and the
output stage is not operative.
Short-circult at the output:
The principle on which the circuit operates is explained only on the basis of the right-hand channel and is of
course also valid for the left-hand channel and the bass channel.
in normal operation, with every positive half
wave via the feedback the base of TS7308
becomes more positive than the emitter. The
transistor
remains
blocked.
D6302
prevents
switching through during the negative haif wa-
ve.
If during the short-circuit at the output the si-
gnal being fed back falls away, in the case of
the positive half wave
the emitter becomes
more positive than the base. TS7308 is con-
ducting. D6308 is for a positive pulse in the
conducting direction. Via R3274 this positive
pulse reaches the base of TS7287 and swit-
ches the latter through. The astable monoflop switches off the output stage, as described under fault +/-DC pulse,
for 4-5 seconds. Due to threshold voltages (7308, 6308, 7287), this short-circuit interruption will only operate from
around 1.4Veff at the output of IC7322.
7322
Feedback
Fig. 1
9 Gs)
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