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the permission of Dolbyized FM broadcasting, set the switch to 25uS position. This automatically
change the time constant to 75uS
while the DOLBY
switch is placed in other than DOLBY
FM positions (namely normal FM broadcast position), thus, the de-emphasis time constant for
each normal and Dolbyized FM reception will be correctly set.
13.
POWER
AMPLIFIER
Differential amplifier consists of the transistors H701 and H703 to provide satisfactory D.C.
stability.
The transistor H705 drives the inverter transistors H711 and H713 which, in turn, drive the
power stage consisting of HOO1 and HOO2. Transistors H707. H709 and H720 are current limiter
operating as a power transistor protection circuit.
Excessive current flow in the power output stage is detected by the resistors R742 and R744
and the resultant variation is applied to the transistors H707 and H709 and make them turned on.
This decreases the base biasing current for H711 and H713. In this way the current flow in the
power output stage (HOO1 and HOOZ2) is restricted within a safe predetermined value.
14.
BTL (Balanced Transformer-Less) CONNECTION
This power amplifier is designed to operate in either 2-channel or 4-channel modes, depending
on the setting of the AMPLIFIER
MODE
switch that incorporates phase-conversion and power
switch for BTL connection.
With this switch placed in the 25Wx4 position, this unit operates as a 25W 4channel amplifier.
With the switch placed in the 70Wx2 position, the unit operate as a 7OW 2 channel amplifier,
in which case, the power output is obtained only from FRONT SPK terminals.
15.
POWER
SUPPLY
UNIT
The power supply unit consisting of transistors H801, H802 and H803, which operates as an
automatic
voltage regulator provides +35V
DC to all of the audio amplifiers except power
amplifiers, and H804 which operates as the voltage regulator provides +14V DC to the tuner
section, and H805, H806 and H807 which operates as the speaker protector to relay circuit.
16.
AUDIO TROUBLE
ANALYSIS
1. Excessive line consumption
a.
Check for shorted rectifiers H812 through
H815.
b.
Check for shorted transistors HOO1 through
HOoOo8.
c.
Check L007 for short.
2. No line consumption or zero bias
a.
Check line cord, fuse, shorted HOO9 through
HO10.
b. Check for open rectifiers H812 through H815,
or open L007.
a.
Check filter capacitors C006, C007 & C705.
b.
Check for shorted transistor H801.
4, Parastic oscillation
a.
Check for defective capacitors, C707, C708,
C719, C720, C721 & C722.
5. Improper clipping
a.
Check for defective resistor, R762 & R763.
3. Excessive hum and noise level
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