Quad Electroacoustics QUAD 405, Сервисные данные, Страница: 6 / 24

FAULT FINDING
6
The following information may assist in locating faults occuring on the amplifier boards of a 405.
In each case only the faulty channel of the 405 is driven, as in the test procedure. The input should be
a sine wave of 0.5V RMS and the output should be applied to an 8„ load unless otherwise stated.
The numbers refer to the relavent test check.
*Board type M12368 only **Board type M12565 only.
Effect Cause
1.
R33 Burnt Collector-Base Tr10 o/c
R37 Burnt L1 o/c (solder joints)
R41 Burnt L3 o/c (solder joints)
R39 Burnt R20 or R21 o/c
R38 Burnt D5 or D6 o/c
2.
High Current Tr2 o/c, Tr3 o/c, Tr7 o/c Tr9 s/c
Tr10 s/c, R7 o/c C8 s/c
* C3 s/c
** D2 o/c R8 o/c
Draws high current which drops to 0.1A
after approx 2 seconds R14 o/c
3.
No increase in a.c. supply current
for increase in signal R3 o/c, C1 o/c, R31 o/c
Signal is unstable and clips R6 o/c
100W output for 0.3V input R20 or R21 o/c
Waveform trace as in Fig. 3 Tr8 o/c, Tr6 s/c, R36 o/c, R30 o/c, C10 s/c
Waveform trace as in Fig. 4 L2 o/c (solder joints)
Approximately 4W output R16 o/c
4.
Second Harmonic Distortion IC1, Tr1, Tr2, Tr3, Tr4, R5, R6, R17, R18, R22, C1
Second Harmonic Distortion especially at 100Ó C2, C7, C8
and on o/c load
Third Harmonic Distortion especially at 100Ó R5
Third Harmonic Distortion L2, R3, R6, R16, R20, R21, C3
Hum and Noise C5 o/c
Hum* R37 o/c
Waveform trace as in Fig. 5* Tr3 s/c
Waveform trace as in Fig. 6* R23 o/c, R5 o/c
Waveform trace as in Fig. 7 R33 s/c
Waveform trace as in Fig. 8* R8 o/c
Waveform trace as in Fig. 9 C5 s/c, R15 o/c, Tr1 o/c
6.
Distortion at 20Ï D5 or D6 s/c,
8.
Liimiting resistor R11 has no effect R10 s/c
9.
Square Wave trace as in Fig. 10 C6 o/c
10.
Noise especially at 100Ó R5
Noise with large spikes Tr1
Noise R12, R3, R4, Tr2, IC1 (change to topology!)
11.
Current limiting check with 1„ load
Waveform trace as in Fig. 12 R29 o/c, R28 s/c, R25 o/c
Waveform trace as in Fig. 13 D3 s/c, R27 o/c, R24 o/c, R26 s/c
Waveform trace as in Fig. 14 Tr6 o/c
Waveform trace as in Fig. 8 C11 s/c Tr5 o/c
13.
Draws high current with 6V d.c. supply T2 s/c