Jvc TX 55 Service Manual

Page 1

"'FSE'EE

COMPUTER CONTROLLED TUNER

No. 2602
MAR. 1982

Page 2

Contents

PPN.

0,01

\l

1

Page
Specifications ........................ 1
Service Precautions ..................... 1
Names of Controls and Their Functions ....... 2
Explanation of New Technology ............
4-(1) Introduction to T-X55 ............... 4
4-(2) Operation Principle of Dual-Slope
A/D Converter .................... 4
4-(3) Operation Principle of A/ D Converter ..... 5
4(4) Functions of Microcomputer
(uPD1404C-527) .................. 6
. Block Diagram ........................ 7
. Main Parts Locations .................... 8
6-(1) Top View ....................... 8
6-(2) Front View ...................... 8
6-(3) Rear View ....................... 8
. Exploded View and Part Numbers ........... 9
. Tuner Alignment Procedures ............... 10
8-(1) Frontend Section .................. 10
8-(2) IF Detection Section ................ 10
8-(3) Alignment of FM dB Indicator ......... 11
8-(4) MPX Section ..................... 11

. Specifications

FM TUNER SECTION

Tuning Range
Usable Sensitivity

: See back cover
: 10.3 dBf (0.9 V175 ohms)

50 dB Ouieting Sensitivity

MONO (75 ohms)
STEREO (75 ohms)

; 16.4 dBf(1.&41VI
: 31.0 dBf (9.8 pvl

Signal-toNoise Ratio

MONO/STEREO

: 84 dB/80 dB

Total Harmonic Distortion

MONO (1 kHz) : 0.07 %

STEREO (1 kHz) 10.07 %
Capture Ratio : 1.0 dB
Alternate Channel

Selectivity : 80 dB
Image Response Ratio : 80 dB
IF Response Ratio 1 105 dB
Spurious Response Ratio: 100 dB
AM Suppression : 67 d8
Stereo Separation

(1 kHz) : 50 dB

Frequency Response

2

2 30 Hz - 15 kHz (+0.3, -1.0 dB)

. Service Precautions

Note that the following symptoms are not troubles.

(1)

T-X55

Pressing the dB indicator button interrupts sound
momentarily.

This unit incorporates a facility to measure the input
field strength up to 100 dB. When the field strength
exceeds 55 dB and 65 dB, the attenuator is automati~
cally set. Therefore, when the attenuator is automati-
cally set or cleared, the RF signal is irregularly modu-
lated (FM) which comes out as noise. To cancel the
noise, the muting facility is momentarily operated to
mute the sound.

No.2602

8-(5) AM Section ...................... 11
8-(6) Alignment of AM dB Indicator ......... 11
9. Printed Circuit Board Assy and Parts List ...... 12
9-(1) TXX-384 Tuner P.C. Board Ass'y ..... 12
9-(2) TXX-385 Logic & Display P.C.
Board Assy ............. 16
9-(3) TPS-ZGSC Voltage Selector P.C.
Board Ass'y ............. 21
9-(4) TPS-3ZOB/C Fuse P.C. Board Ass'y ...... 21
10. T-X55 Schematic Diagrams ................ 18
11. Packing Materials and Part Numbers .......... 21
12. Accessories List .................. back cover
13. Parts List with Specified Numbers for
Designated Areas ................. back cover
14. Power Specifications and Tuning Range . . back cover

Warning:
When replacing the parts marked with A , be sure to
use the designated parts to ensure safety.

Subcarrier Suppression

Antenna Input
Impedance

Output Signal Level

REC CAL Output Level

: 73 dB

: 75 ohms unbalanced
300 ohms balanced

: 600 mV (2.2 kohms)

: Equivalent to 50 %
FM modulation

AM TUNE R SECTION

Tuning Range
Usable Sensitivity

: See back cover
2 20 11V (External antenna)

Total Harmonic

Distortion : 0.3 %
Signal-to-Noise Ratio : 50 dB
Selectivity : 32 dB
Image Response Ratio : 40 dB
I'F Response Ratio : 65 dB

Output Signal Level ; 200 mV (2.4 kohms at 30 %
MOD)

GENERAL

Dimensions (W x H x D) :

Weight

435 x 77 x 315 mm
17-1/8 x 3 x 12-7/16 inches
: 3.2 kg (7.1 lbs.)

Design and specifications subject to change without notice.

(2) The reception sensitivity of the memorized station is

low.

As the attenuator is automatically set according to the
field strength, when a station is memorized with strong
field strength input, the attenuation level is main-
tained irrespective of subsequent variation of field
strength.,Therefore, when the field strength is reduced
(due, for example, to shift of antenna direction) after
the station is memorized, the attenuator is kept in
operation, resulting in seemingly poor sensitivity. At
this point, rememorize the station. By so doing, the
attenuator is automatically cleared.