Technics RS-M228X - Page 13

Check of control
circuit in dbx circuit
Equipment
* DC volt meter
NOTE:
RS-M228X
CHECKING METHOD
E.C.B (G.S.D) voltage check of each switching transistor for Encode/Decode
The terminal voltage of each switching transistor in Encode/Decode mode are shown in the table below
Decode (dbx tape)
C (S) B (D)
OV OV
OV OV
Encode (dbx tape)
eE@ | co | 80 [| €@ |
—01V [| ov ov —0.03V
~0.08V ov ov ov
-0.22V | 10.53V —0.19V
—051V | 10.52V -0.5V
—o.0av | —0.22v | —0.19V
0.01v. | —0.51V —0.46V
=0.22V | -0.22V | ov
—05V | —05V | ov
ov Ov
ov ov
—0.16V ov
—0.15V ov
ov —0.16V
ov —0.15V
—0.16v | —0.16V
—0.15V | —0.15V
|
|
Transistor
Ref. No.
Q201
Q202
Q203
Q204
Q205
Q206
Q207
Q208
Q209
Q2
Q2
Q2
Q2
Q2
Q2
Q2
Q2
Q2
Q2
OV —0.08V
OV 0.01V
—9.08V | —0.08V
—10.64V | —0.33V
—1.53V 10.52V
OlLOINI Dm! R]Wlrmo]e fo
© If no abnormality is found in steps J and @2 check the operation for each part as follows:
Operation check of
INPUT BAND PASS
FILTER circuit
(27 Hz— 20 kHz)
Condition
* Record mode
* Input level controls --- MAX
* Noise reduction selector
+ dbx tape
Equipment:
*VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600 2)
Operation check of
VCA circuit and
Pre-emphasis/
De-emphasis circuit
Condition:
* Stop/record mode
* Input level controls --- MAX
* Noise reduction selector
-- disc/dbx tape
Equipment:
*VTVM * AF oscillator
* ATT + Oscilloscope
* Resistor (600 2)
1. Make the connections as shown in fig. 14, and
apply 100Hz — 274dB signal from LINE IN, and
set the noise reduction selector to dbx tape
position
Set the unit to record mode
Adjust ATT so that the signal level at TP201
L-CH) and TP202 (R-CH) is 300 mV.
ake sure that the emitter signal level of Q203
L-CH) and Q204 (R-CH) is 300 mV
Set the input signal frequency to 5kHz and
make sure that the emitter signal of Q203
L-CH) and Q204 (R-CH) remains at the same
evel (300 mV).
4 Q203 (L-CH)
TP203{(L-CH)
)
dbx
circuit
boar
204
(R-CH)
— TP204{R-CH) J “VTVM Osslloscope
_— ae
> STPOOOO] F |
ae
A
AF
oscillator
AT
=
6002/
ae
esistor, ait ere
LINE IN dbx circuit toard
VTVM_ Oscilloscope
Fig. 14
GJ-1 Operation check of VCA circuit and Pre-emphasis circuit
1. Make the connections as shown in fig. 15, and
apply 1OOHz —27dB signal from LINE IN.
2. Short pin @ of IC201 (L-CH) and IC202
(R-CH) to TP207 (ground) as shown in fig.
16
3. Set the unit to record mode, and set the noise
reduction selector to dbx tape position.
4. Adjust ATT so that the signal level at TP201
(L-CH) and TP202 (R-CH) is 300 mV.
5. Make sure that the output signals at TP203
(L-CH) and TP204 (R-CH) are sinusoidal.
(The operation of VCA can then be checked.)
6. Shift the frequency of input signal to 5kHz, and make sure that
the output signal levels at TP203 (L-CH) and TP204 (R-CH)
are increased by about 12 dB.
(The operation of the Pre-emphasis circuit can then be checked.)
TP203 (L-CH)
TP204(R-CH) VIVM Oscibsco pe
TP201 (L-CH) |
1P202(R-CH)
LINE IN
ATT
Resistor
AF oscillator
VTVM Oscilloscope
Fig. 15
10201 (1 -CH)
1€202(R-CH)