Jvc CD 1635 Mk2 Service Manual Supp

Page 2

CD-1636/C

CD-1635Mark II J

Main Adjustments

[I] Equipment and measuring instruments used for adjustment.

Electrical adjustment
1) Electronic voltmeter

2) Audio frequency oscillator
(range; 50-20kHz and output OdB with impedance

60052)
3) Attenuator

4) Standard tapes for REC/PB
Maxell UD - for "NORM" position
TKD SA -- for Cr02" position

5) Reference tapes for playback (JVC Test Tape)
VTT-658 (for head azimuth adj.)
VTT-664 (for Reference level 1kHz)
VTT-675N (for playback frequency response)

6) Resistors

10052 (for measurement of the bias current)
60052 (for attenuator matching)

Audio F req. Osc.

} or equivalent

[II] Electrical circuit adjustment procedure

Adjustment should be performed in the order of steps 1,2,3.

Playback system

Electronic

Attenuator

CD-1 636/ C
CD-1635-2A/B/E/U

Voltmeter, .-
/ -

Step Item Adjustment 235:?" 8323; Remarks
1 Level meter 1. Set the deck in the record mode. R134 VU meter Perform the adjustment when
deflection R234 reading:0 the parts are replaced.

2. Input 1kHz signals to MIC or LINE
IN jacks (with a level of -60st
(0.78mV) approx. for MIC input or
~10st (24QmV) approx. for LINE
IN input.)
Adjust the recording volume controls
so that the voltage across LINE OUT
is ~35st (518mV).

3. Adjust two semi-fixed variable
resistors R1341Loch) R234(R-ch) so
that the level meters indicate zero VU.

2 Play back Adjust R115 and R215 to obtain zero R115 VU meter 1. Adjust reproduction level
level VU meter reading using reference tape R215 reading: 0 when heads are replaced.

VTT-664 (old ref. no. TMT-6009). 2. Make this adjustment after
Set equalizer switch in "NOR MA L" making sure level meter
position and turn off AN RS switch deflection angle is correct.
when adjusting play back level.

3 Checking the Play back the VTT-675N test tape. Standard frequency: The 1kHzoutputwith
playback fre- Check to see if the outputs at the fre~ 1kHz the equalizer switch
quency response quencies conform to the standard "NORM" position; set to NORMALrefers

levels. +2.5dBi3dB at 63Hz to Cr02 position.
OtSdB at 10kHz
"Cr02" position
+2.5dBt3dB at 63Hz
-4.5dBi3dB at 10kHz

No. 41452

Page 3

Recording system

CD-lS36/C
CD-I 635Mark ll

R/P HEAD (E. voltmeter)

INPUT

If no measuring apparatus is available,
check in the following way.

Music sound is not sonorous in the
high range on playback: bias current is
too high.

Music sound is also sonorous in the
high range on playback but distorted:
bias current is too low.

Step Item Adjustment Aflgfiltng 353:, Remarks
1 Checking Record lkHz, 50Hz and 10kHz signals Reference frequency; This checking should

record/playback at an input level of OVU ~20dB. lkHz be performed for nor

frequency res- Play back the tape. With a normal tape mal and chrome tapes

ponse Check to see that the 50Hz and 10kHz 0i3d8 at 50Hz and for both right and
signal output deviations fall within the 0t3dB at 10kHz Ieit channels. Adjust-
standard range, using the lkHz signal With a chrome tape ment is performed
output as a reference. (It is basically Ot3dB at 50H: with the semi~fixed
desirable that the lkHz, 50Hz and OtSdB at 10kI-lz resistors for bias
10kHz signal outputs are the same.) current adjustment.

2 Recording bias Record 1kHz, 50Hz and lOkHz signals For Output 1. Bias Current adjustment for
at an input level of OVU ~20dB. Play normal deviation: a cassette deck should genera-
back the tape. tape 0 My be performed referring to
Adjust R555 and R557 (for a normal R555,557 the record/playback frequen-
tape), R556 and R558 (for a chrome cy response. This is because
tape) until the indicated deviation of For the frequency response of a
the 10kHz signal output from the chrome cassette deck depends more
lkHz signal output becomes 0. tape greatly upon the bias current

R556.558 than does that of an open reel
deck. The current measuring
method described below is an
alternative one.

2. If the bias current is not pro
perly adjusted, the record and
playback characteristics be-
come as shown below.

Alternative'methode NORM: Approx. Increase w i...» "as...
1. Set the deck in the record mode. R555,557 37mV _ '"' """""°"
2. Connect a 1009 resistor in series 3 \

with ground wire of head (recording 5 122,

model E meantime?
3. Connect the Electronic voltmeter Cr02: Approx. sou. m4. mm:

across the resistor, and measure its R556,558 47mV Fruuumv ma

voltage. (BIAS ADJ)

l. in order to distinguish the
ground terminal of the head
from its live terminal, touch
the terminals with a finger
while the deck is in the play-
back mode. The VU meters
deflect when the ground
terminal during recording is
touched. (For a record/play-
back head, the polarity is
reversed aocording to whether
recording or playback.)

2. Be sure to employ a shielded
wire.

3. Be sure to connect resistor to
head terminal not PCB side.

No. 4145-2