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GfQnaL AUDIO
When this diode is held above the objective unit, the
infrared light falls on the 4 photodiodes.
When the 4 photodiodes are functioning, the following
voltage form will be visible on test point 4, 6, 7 and 8 on
the panel.
(The amplitude depends on the distance between the IR
diode and the objective).
~ n o
LJ7._J
L
38 31l, A12
Position of the oscilloscope:
100
ms/div.
•
HF-in {pin 3, test point 3)
- The HF-signal('"' High Frequency in) is the information
signal from the 4 photodiodes.
•
HF-out (pin 27; test point 17)
- The HF-out signal (= High Frequency) is the amplified
information signal for the decoder circuit.
During playback of test disc no. 5
(4822 897
30096), a
so-called "eye pattern" should be present on test point
17 (see figure below).
- The HF signal should be present and stable in:
- The PLAY mode and in
- Servicing position 3 after the lead-in track has been
read.
- In servicing position 2 and during the reading of the
lead-in track, the HF signal is present but is not stable.
HF OUT
Position of the oscilloscope: 0,5 µs/div.
Amplitude about 1,5
V
PP
e DET (pin 26)
42 517 A12
HFD (pin 19; test point 23)
TL (pin 18; test point 16)
- The
DET
signal (= Detector) gives information on the
level of the HF signal to the high-frequency.
Level-Drop-out detector IC6525.
- When the level of the HF signal is too low, the HFD
signfil.J:: High Frequency Detector) will go "low".
- The TL signal (= Track Lost) will then go "low" in order
to tell the servo µP that the tracking signals are
unreliable.
Method:
(Can only be used in a playing set).
-
Put test disc SA 84822 397 30096) on the turntable.
- Switch on the power-supply switch and press the
PLAY key.
-
Play track number
10
or
15
and check the HFD signal
at test point 23.
When drop-out pulses are present on the DET signal
(pin 26), the HFD pulses should also be present at
test point
23.
(Position of oscilloscope: 2 ms/div.).
When the disc is slowly braked by hand, TL pulses will
be visible at test point
16.
•
RE1 (pin 11; test point 18)
RE2 (pin 12; test point 22)
- Signals RE1 and RE2 (Radial Error) are the control
signals for the arm during tracking.
4-5
- In servicing position 2, the following signals should be
visible at test point
18
and
22.
rnn
fl nonn (\
n
OOr
ovv
\Juovcr
0
\JVU
Position of the oscilloscope: 2 ms/div.
The frequency strongly depends on the eccentricity
of the disc.
IV. RADIAL ERROR PROCESSOR IC6529
•
Check the signals between the µP and the Radial
Error Processor
•
DAC (pin 10; test point 38)
With the DAG signal
(=
Digital to Analogue Converter)
the track jumping speed is controlled.
This signal is derived from the signals BO + 83
coming from the µP.
• RE-lag (pin 8; test point 41)
Capacitor 2559 in the RE-lag circuit has a memory
function.
It memorizes the degree of inclination of the disc.
When
a
jump is made to a certain track on the disc,
the memory should be cleared.
This is done by the µP (RPU signal) via transistors
6533, 6534.
During track jumping (SEARCH), slow pulses should
be visible at test point 43 (position of the oscilloscope
0, 1 ms/div.)
In that case pulses should also be visible on the
collector of transistor
6533,
6534.
cs
9 987
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