CHC-TB10, CHC-TB20, HCD-TB20 - Sony Audio Service Manual (repair manual). Page 25

25

INTRODUCTION
When set to the test mode performed in 

,

when the tape is rewound after recording, the “REC memory mode”
which rewinds only the recorded portion and playback is set.
This “REC memory mode” is convenient for performing this
adjustment. During recording, the input signal FUNCTION will
automatically switch to MD.
(After recording, turn the  m/M  knob without stopping will
return to the position where recording was started.)

1.

Press  FUNCTION  button to select MD. (This step is not
necessary if the above test mode has already been set.)

2.

Insert a tape into deck, press the  REC PAUSE/START  button,
and then press the  Y  button to start recording.

3.

Mode: Record

4.

Mode: Playback

5.

Confirm playback the signal recorded in step 2 become
adjustment level as follows.
If these levels do not satisfy adjustment level, adjust the RV652
(L-CH) and RV602 (R-CH) on the TC board to repeat steps 3
and 4.

Adjustment level:
CN322 playback level: 47.2 to 53.0 mV (–24.3 to –23.3 dB)

AF OSC

MD IN
315Hz 50 mV (–23.8 dB)

blank tape
CS-123

set

attenuator

600 

Ω

recorded
position

level meter

set

MAIN board
CN322
Pin 

5

 or TP42 (L-CH)

Pin 

9

 or TP46 (R-ch)

Note :

1. CD Block is basically designed to operate without adjustment.

Therefore, check each item in order given.

2. Use YEDS-18 (3-702-101-01) unless otherwise indicated.
3. Use an oscilloscope with more than 10M

Ω

 impedance.

4. Clean the object lens by an applicator with neutral detergent

when the signal level is low than specified value with the
following checks.

Procedure :
1. Connect an oscilloscope to TP (FE1).
2. Connect between IC103 Pin qj TP (FEI) and TP (DVC) (1.65 V)

by lead wire.

3. Turn the power on.
4. Load a disc (YEDS-18) and actuate the focus search. (In

consequence of open and close the disc tray, actuate the focus
search)

5. Confirm that the oscilloscope waveform (S-curve) is

symmetrical between A and B. And confirm peak to peak level
within 2 ± 0.5 Vp-p.

6. After check, remove the lead wire connected in step 2.

Note :

• Try to measure several times to make sure than the ratio

of A : B or B : A is more than 10 : 7.

• Take sweep time as long as possible and light up the

brightness to obtain best waveform.

Procedure :
1. Connect an oscilloscope CH1 to TP (RFDC) and CH2 to TP

(RFAC).

2. Turn Power switch on.
3. Load a disc (YEDS-18) and playback the number five track.
4. Confirm that oscilloscope waveform is clear and check if RF

signal level is correct or not.

BD board

oscilloscope

TP(FE1)
TP(DVC)

symmetry

S-curve waveform

within 2 

±

0.5Vp-p

A

B

TP(RFDC)

BD board

oscilloscope

TP(DVC)

TP(RFAC)
TP(DVC)

CH1 CH2