Teac A-450 - TROUBLE-SHOOTING

9. TROUBLE-SHOOTING
NOTE
REF. No’s indicated in the following table refer to the left
channel, for the right channel REF. No. identification, see
schematic diagram.
TAPE TRANSPORT SECTION
1.
Fuse blows when POWER is switched ON
— Defective Power Transformer
Auto End-stop will not work in Play and/or Fast Wind.
+B voltage not present between terminal A of SCR and
GND.
— Defective Resistor R307
— Defective Diode D302
Solenoid will not energize when SCR terminals A and
K are switched ON.
— Defective Switch $109
— Defective Solenoid
Solenoid will not work when SCR terminals A and G
are shorted together.
— Defective SCR
Tape winds onto Capstan Shaft.
— Defective Pinch Roller
Defective Take-up Reel Table Ass’y
Idler slipping
Tape path wrong (improper Tape Guide position
bad Head mounting)
|
Excessive Wow and Flutter
— Defective Pinch Roller, Pinch Roller pressure
incorrect
— Capstan Belt stretched or oily
Capstan does not rotate
— Capstan Belt off
— Defective Motor
Index Counter will not count
— Counter reset button not fully depressed.
— Counter Belt off
AMPLIFIER SECTION
1.
No sound in playback mode
Noise (hum or clicking noise) appear when touching
head wires.
— Poor soldering of head terminations
— Defective Head
Sound can be heard during recording
— Defective Switch S101
— Defective Transistor Q101, Q102
— Defective Parts associated with parts indicated
above
Sound cannot be heard during recording.
— Defective Transistor Q101, Q102, Q103
— Defective Dolby NR Circuit
— Defective Parts associated with parts indicated
above
Level Meter will not indicate in playback mode.
— Defective Level Meter
— Defective Transistor Q107
— Defective Semi-fixed Resistor VR107
— Defective Parts associated with parts indicated
above
Loss of high frequencies in playback mode
High frequencies too low
— Defective Transistor Q102
— Playback equalizer circuit wrong
High frequencies are several dB below specified re-
sponse limits
— Head dirty or defective
Loss of high frequencies including level variation
— Improper head-to-tape contact
— Unstable functioning of tape transport me-
chanism
Poor playback signal-to-noise ratio
Excessive hum — reduced when changing Power Trans-
former.
— Defective Power Transformer
Excessive white noise (hiss and circuit noise)
— Defective Head
— Defective Transistor Q101, Q102
— Associated circuitry of Transistor Q101, Q102
Wave form varies continuously
— Defective Transistor Q101, Q102
— Defective Capacitor C 102, C108
— Defective Parts associated with parts indicated
above
Does not record
Can record when changing Bias Switch setting
— Defective Bias Switch
— Defective Trimmer Capacitors VC101, VC102,
VC103
— Defective Parts associated with parts indicated
above
Cannot erase, also
— Bias Oscillator Ass’y faulty
Can erase — sound from record monitor mode is
normal
— Head dirty
— Defective Transistor Q105, Q106
— Defective Switch $101
— Defective Circuitry of Q105, Q106
29