Onkyo TX-7900 User manual

Ref. No. 3420
ONKYO
SERVICE
MANUAL
QUARTZ SYNTHESIZED
TUNER AMPLIFIER
MODEL TX-7900
MODEL TX-7920
Black and Silver models
SAFETY-RELATED COMPONENT WARNING! !
COMPONENTS IDENTIFIED BY MARK A ON
THE SCHEMATIC DIAGRAM AND IN THE PARTS
LIST ARE CRITICAL FOR RISK OF FIRE AND
ELECTRIC SHOCK. REPLACE THESE COMPO-
NENTS WITH ONKYO PARTS WHOSE PART
NUMBERS APPEAR AS SHOWN IN THIS
MANUAL.
MAKE LEAKAGE-CURRENT OR RESISTANCE
MEASUREMENTS TO DETERMINE THAT EXPOSED
PARTS ARE ACCEPTABLY INSULATED FROM
THE SUPPLY CIRCUIT BEFORE RETURNING
THE APPLIANCE TO THE CUSTOMER.
ONKYO
AUDIO COMPONENTS
TABLE OF CONTENTS
Specifications eee errr ee eee eee eee ee eee Tee eee eee eee ere Terre ree eee ere 2
Service procedures::+++i+sssssssstssesesesseeesseeseseeseserseeageeens 3
Exploded view Model TX-7920++:+++:+++s+sssesseseseeeeseeessseeneens 4
Parts Ist Model TX-7920 tse: wvesncwses ceracmmamninsaeennenee 5
Exploded view Model TX-7900++++++++++:ssess+sessesesseeereeesaeeens 6
Parts list Model ‘TX-7900 issssster<eomnns sane venwavanes senna canon cones 7
Block diagram Model TX-7920-++++1:+++ssessseerseeesseersese seeeees 8
Block diagram Model TX-7900-+++++:++1s+sessseerseseseeteseeeeeeeens 9
IC block diagram and descriptions::::::1++++sseeeseseeseeseerees 10
Packing view svrcessscessceeeseeessseeseessenseneeseesesescnesensereanneens 17
Adjustment procedures ree eee eee eee er errr) 18
Printed circuit board view from bottom side-+r+++++rrr + est+* 21
Schematic diagram
Model "P7920: sere: ose cwaes uedewvensaes eonnenamenaee eemaseeeninenl 23
Model TX: 7900» «sss sentecnnsaxonenen nonce dvtineanennasaerawargicaeenines 25
Printed circuit board-parts list
Model “TX. 7620 se2nesenses ary deanwians sccswansapanvagis narangianane gies sen 29
Model 1X. 20 0Gxrtceswens corweswaieaee dennwonatennigipien vpeiciirnay 9 tate wea 39
TX-7900/TX-7920

TX-7900/TX-7920
SPECIFICATIONS
AMPLIFIER SECTION
Power Output:
Dynamic Power Output:
Continuous Power Output:
Total Harmonic Distortion:
1M Distortion:
Damping Factor:
Frequency Response:
RIAA Deviation:
Sensitivity and Impedance:
Phono Overload:
Signal-to-Noise Ratio:
Tone Controls:
Muting:
LOUDNESS (—30dB):
TUNER SECTION
FM:
Tuning Range:
TX-7920
60 watts per channel, min. RMS, at 8 ohms, both
channels driven, from 40Hz to 20kHz, with no more
than 0.2% THD.
2 X 100 watts at 4 ohms
2 X 75 watts at 8 ohms
2 X 80 watts at 4 ohms, 1kHz (DIN)
2 X 65 watts at 8 ohms, 1kHz (DIN)
0.2% at rated power
0.1% at 30 watt output
0.2% at rated power
0.1% at 30 watt output
50 at 8 ohms
20 — 30,000 Hz + 1dB
20 — 20,000 Hz + 0.8dB
Phono: 2.5mV 750 kohms
CD/Tape Play: 150mV_//50 kohms
Tape Rec: 150mV//3.5 kohms
120mV RMS at 1kHz, 0.2% TDH
Phono: 80dB (at 5mV input, IHF-A)
CD /Tape: 100dB (1HF-A)
Bass: + 10dB at 100Hz
Treble: + 10dB at 10kHz
— ©
+7dB at 70Hz, +5dB at 10kHz
87.50—108.00MHz (50kHz steps)
TX-7900
45 watts per channel, min. RMS, at 8 ohms, both’
channels driven, from 40kHz to 20kHz, with no more
than 0.3% THD.
2 X 80 watts at 4 ohms
2 X 60 watts at 8 ohms
2 X 60 watts at 4 ohmsm, 1kHz (DIN)
2 X 50 watts at 8 ohms, 1kHz (DIN)
0.3% at rated power
0.1% at 30 watt output
0.3% at rated power
0.1% at 30 watt output
50 at 8 ohms
20 — 30,000 Hz + 1dB
20 — 20,000 Hz +0.8dB
Phono: 2.5mV 7/50 kohms
CD/Tape Play: 150mV/50 kohms
Tape Rec: 150mV//3.5 kohms
120mV RMS at 1kHz, 0.3% THD
Phono: 80dB (at 5mV input, |HF-A)
CD/Tape: 100dB (IHF-A)
Bass: + 10dB at 100Hz
Treble: + 10dB at 10kHz
+7dB at 70Hz, +5dB at 10kHz
Mono: 12.4dBf, 1.2“V, 750hmd.
1.2”V (S/N26dB, 40kHz Devi.)
750hms DIN
Stereo: 19.2dBf, 25"V, 750hms
25“ (S/N 46dB, Devi.)
750hms DIN
Mono: 18.2dBf, 2.2“V, 750hms
Stereo: 38.2dBf, 22“V, 75ohms
Usabls Sensitivity:
50dB Quieting Sensitivity:
Caputure Ratio: 1.5dB
Image Rejection Ratio: 85dB
IF Rejection Ratio: 90dB
Signal-to-Noise Ratio: Mono: 70dB
Sterep: 65dB Stereo: 65dB
Selectivity: 50dB DIN (+300kHz, 40kHz dev.)
AM suppression Ratio: 50dB
Harmonic Distortion: Mono: 0.15%
Stereo: 0.30%
30—15,000H2+1.5dB
40dB at 1kHz
30dB at 100—10,000Hz
17.2dBf, 44¢V
Frequency Response:
Stereo Separation:
Muting Level:
AM:
Tuning Range: 522—1610kHz (9kHz steps)
522—1610kHz (9kHz steps) or
530—1710kHz (10kHz steps) (World wide model)
Usable Sensitivity: 30nV
image Rejection Ratio: 40dB
{IF Rejection Ratio: 40dB
Signal-to-Noise Ratio: 40dB
Harmonic Distortion: 0.8%
GENERAL TX-7920 TX-7900
Dimensions (WXHXD): 455 120X316mm 455X120X316mm
17-15/16" X4-6/8" 12-716" 17-15/16" X4-6,8" X12-7//16"
Weight: 8.0kg, 17.6 Ibs. 7.2kg, 15.9 lbs.

1p Cracleeyap racy Ae)
Remote control transmitter RC-223S (Only Model TX-7920)
Transmitter: Infrared
Signal range: Approx. 5 meters (16ft. X 4” )
Power supply: Two “AA” batteries(1.5V X 2)
Specifications and features are subject to change without notice.
SERVICE PROCEDURES
1.Replacing the fuses 4.Memroy preservation
For continued protection against fire hazard,replace This unit does not require memory preservation batteries.
only with same type and same rating fuse. A built-in memory power back-up system preserves contents
Circuit No. Part No. Description Model of the memory during power failures and even when the
: 7 unit is unplugged. The unit must be plugged in and the
Foz pa ese Eee SCE power switch turned on and off once im order to charge the
F902 252075 2.5A-SE-EAK, Primary TX-7920 back-up system. Note that since this is not a permanent
F951 252074 2A-SE-EAK,AC outlet TX-7920 memory,the power switch must be turned on and off a few
times each month to keep the back-up system operative.
2.Safety-check out The period of time during which memory contents are
After correcting the original service problem,perform preserved after power has last been turned off varies
the following safety check before releasing the set to depending on climate and placement of the unit.
the customer. On the average, memory contents are protected over a
Connect the insulating-resistance tester between the period of 3 to 4 weeks (a minimum of 2 weeks) after
plug of power suuply cord and nickel screw on the back the last time power has been turned off. This period is
panel. shorter when the unit is exposed to very high humidity or
Specifications: More than 10M 0 used in an area with an extremely humid climate.
3.Changing the band step
A BAND STEP selector switch is not provided.
R707 85

TX-7920
EXPLODED VIEW
MODEL TX-7920

PARTS LIST
REF.NO. PARTNO. DESCRIPTION REFNO. PART NO. DESCRIPTION
1 27110680Y Front bracket <B> 87 2832A1T1Y Knob SP B <B>
27110681Y Front bracket <S> 28324173Y Knob SP B <S>
4 28133254Y¥ Back plate 91 27300833 WS-2NS,Clamp
5 27100228Y Chassis F902 252075 A\ 2.5A-SE-EAK Fuse
6 27160293Y Radiator F951 252074 A 2A-SE-EAK,Fuse
7 27141441Y Bracket LH P901 253164Y or A AS-CEE,
8 27141442Y Bracket RH 253175Y Power supply cord
9 27141443Y Bracket PC Q503,Q504 2202282, 2SA1265N-R,
12 27130643AY Bracket,shield 2202283, 2SA1265N-0,
13 27121535-2Y Back panel 2201693, 2SA1491-0,
14 27300750 A Bushing 2201694 or 2SA1491-Y or
16 27190524 KGLS-14R,Holder 2201696 2SA1491-P,Power amplifier transistor
17 27190266 KGLS-12R,Holder Q505,Q506 2202292, 2SC3182N-R,
21 834430088 3TTS+8B(BC),Self-tapping screw 2202293, 2SC3182N-0,
22 831130088 3TTW+8B,Self-tapping screw 2201703, 2S8C3855-O,
23 830440089 4TTC+8C(BC),Self-tapping screw 2201704 or 2SC3855-Y or
24 833430080 3TTP+8P(BC),Self-tapping screw 2201706 2SC3855-P,Power amplifier transistor
25 82143006 3P+6FN(BC),Pan head screw T901 2300754Y A NPT-1129P,Power transformer
26 801433 3SMS10W.SW+14B(BC),Sems Ul 1A331525-1A NARF-4325-1A,Tuner circuit pe board
| self-tapping screw ass'y
oa 31 28184471AY Top cover U2 1A331526-1A NADIS-4326-1A,Display circuit pe
| 32 834430088 3TTS+8B(BC),Self-tapping screw board ass'y
33 28140680 0.5 X 180 X8,Cushion U3 1A331527-1A NAAF-4327-1A,Power amplifier circuit
34 27270212 Spacer <P/W/Q> pe board ass’y
51 1A333701K Front panel ass'y <B> U4 1A331528-1A NASW-4328-1A,Headphone terminal
1A334701K Front panel ass'y <S> pe board ass'y
52 28125226BY End cap L US 1A331529-1 NASW-4329-1,Power switch pc board
53 28125227BY End cap R ass'y
58 28191617Y Clear plate U6 1A331530-1 NAETC-4330-1,Terminal pe board ass'y
59 833430080 3TTP+8P(BC),Self-tapping screw U7 1A331531-1A NAPS-4331-1A,Power supply circuit
60 28135199 Badge pe board ass'y
61 27175254 Leg U9 1A331533-1 NAETC-4333-1,AC outlet pe board
62 834430088 3TTS+8B(BC),Self-tapping screw ass'y
71 25060044 Terminal GND U10 1A331534-1A NAAF-4334-1A,Tone control circuit
81 28324162Y Knob LOUD <B> pe board ass'y
28324177Y Knob LOUD <S> Uli 1A331535-1 NAETC-4335-1, Volume control pe NOTE: <B>:Black model only
82 28324150-1Y Knob LEV <B> board ass'y <S>:Silver model only
28324151 Knob LEV <S> U12 1A331537-1 NAETC-4337-1,Terminal pe board ass'y
83 28324163 Knob VOL <B>
aadcke Ener SS : THE COMPONENTS IDENTIFIED BY MARK A
& saeco Sega ARE CRITICAL FOR RISK OF FIRE AND
28324184 Knob POW <S> ELECTRIC SHOCK. REPLACE ONLY WITH
86 28324170Y Knob SP A <B> PART NUMBER SPECIFIED.
28324172Y Knob SP A <S>
4
ios
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TX-7900
EXPLODED VIEW
MODEL TX-7900

PARTS LIST
REF.NO.
1
12
13
14
16
17
21
22
23
25
26
31
32
33
34
31
52
33
38
59
61
62
71
81
82
83
85
PART NO.
27110680Y
27110681Y
28133255Y
27100228Y
27160290Y or
27160272AY
27141441Y
27141442Y
27130643AY
27121536-2Y
27300750
27190524
27190266
834430088
831130088
830440089
833430080
82143006
801433
28184471AY
834430088
28140680
27270212
1A337701K
1A338701K
28125226BY
28125227BY
28191617Y
833430080
28135199
27175254
834430088
25060044
28324162Y
28324177Y
28324150-1Y
28324151
28324181
28324182
28324140
28324184
DESCRIPTION
Front bracket <B>
Front bracket <S>
Back plate
Chassis
Radiator
Bracket LH
Bracket RH
Bracket,shield
Back panel
A Bushing
KGLS-14R,Holder
KGLS-12R,Holder
3TTS+8B(BC),Self-tapping screw
3TTW+8B,Self-tapping screw
4TTC+8C(BC),Self-tapping screw
3TTP+8P(BC),Self-tapping screw
3P+6FN(BC),Pan head screw
3SMS10W.SW+14B(BC),Sems
self-tapping screw
Top cover
3TTS+8B(BC),Self-tapping screw
0.5 X 180 X8,Cushion
Spacer
Front panel ass'y <B>
Front panel ass'y <S>
End cap L
End capR
Clear plate
3TTP+8P(BC),Self-tapping screw
Badge
Leg
3TTS+8B(BC),Self-tapping screw
Terminal GND
Knob LOUD <B>
Knob LOUD <S>
Knob LEV <B>
Knob LEV <S>
Knob VOL <B>
Knob VOL <S>
Knob POW <B>
Knob POW <S>
REF.NO.
86
87
91
F902
P901
Q503,Q504
Q505,Q506
T901
Ul
U2
U3
U4
U6
UT
U10
U12
PART NO.
28324170Y
28324172Y
28324171
28324173Y
27300833
252074
253164Y or
253175Y
2202492,
2202493,
2202243,
2202244 or
2202246
2202502,
2202503,
2202253,
2202254 or
2202256
2300758Y
1A335525-2A
1A335526-2A
1A335527-2A
1A335528-2A
1A335530-2
1A335531-2A
1A335536-1A
1A335537-2
DESCRIPTION
Knob SP A <B>
Knob SP A <S>
Knob SP B <B>
Knob SP B <S>
WS-2NS,Clamp
ZA 2A-SE-EAK, Fuse
A AS-CEE,
Power supply cord
2SA1264N-R,
2SA1264N-O,
2SA1694-O,
2SA1694-Y or
2SA1694-P,Power amplifier transistor
2SC3181N-R,
2SC3181N-O,
2SC4467-0,
2S8C4467-Y or
2SC4467-P,Power amplifier transistor
A NPT-1130P,Power transformer
NARF-4325-2A, Tuner circuit pc board
ass'y
NADIS-4326-2A,Display circuit pe
board ass'y
NAAF-4327-2A,Power amplifier circuit
pe board ass'y
NASW-4328-2A,Headphone terminal
pe board ass'y
NAETC-4330-2,Terminal pc board ass'y
NAPS-4331-2A,Power supply circuit
pe board ass'y
NAAF-4336-1A,Tone control circuit
pe board ass'y
NAETC-4337-2,Terminal pc board ass'y
NOTE: <B>:Black model only
<S>:Silver model only
NOTE: THE COMPONENTS IDENTIFIED BY MARK A.
ARE CRITICAL FOR RISK OF FIRE AND
ELECTRIC SHOCK. REPLACE ONLY WITH
PART NUMBER SPECIFIED.
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TX-7900/TX-7920
IC BLOCK DIAGRAM AND DESCRIPTION
LM7001(PLL synthesizer and controller)
Phase Detector
Charge Pump
. Divider =]
- | Shift Register Latch aoe Latch
31
CE te athe
~10—
Pin No. | Terminal Description
1 XOUT
Connect to the 7.2 MHz crystal oscillator.
3 CE Chip enable terminal. Connect to the PLL terminal of micro processor.
4 CL Serial clock input terminal. Connect to the CLOCK terminal of micro processor.
5 DATA | Serial data input terminal. Connect to the DATA terminal of micro processor.
6 SYN Not used.
é [ 7 AUTO/MONO| Auto/Mono control output terminal. “H” when Auto.
8
BO2
FM
control
signal
output
terminal.
““L”
when
FM.
1
L 9 | BO3 | AM control signal output terminal. ““L” when AM.
10 AMIN AM local oscillator input terminal.
11
FMIN
|
FM
local
oscillator
terminal.
7
L 12 Vop 1 | Power supply terminal for back-up.
13 Vopp2 Power supply terminal.
14
PD1
Charge
pump
output
of
the
phase
detector
which
constitutes
the
PLL.
High
level
is
output
when
sl
divided
local
oscillator
frequency
is
high
than the
reference
frequency.
15
PD2
In
the
opposite
case,
low
level
is
output.
Floating
occurs
when
the
frequencies
matched.
The
output
is
applied
to
the
variable
capacitor
diode
in
the
local
oscillator
through
the
low
pass
| filters.
16 Vss Ground terminal.

TX-7920
4 PD17103CX-528(Remote control decoder)
MODEL TX-7920
| Transminer| AM
Bus
line
Q703
Remote control
decoder
Infrared
XIN GND
X OUT POB2 — STAND-BY
RESET POB1 — RECEIVE
REMIN — PODO POBO — VOL IND
PH SENS — POD1 POC3 — VOL UP
POWER — POD2 POC2 — VOL DOWN
SYSIN — POD3 110] POC1 — PHONO
VDD | 9 | POCO — SYS OUT
Terminal Description
; 1 [xn | OSC Connect to the 8.00MHz ceramic oscillator
System reset terminal. Active low.
Signal input terminal from preamp. for remote control. Active low.
IN Phono detection input terminal. Active low.
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Stand-by detection input terminal. During low input, only the POWER code is decoded
7 POD3 YS IN System code input terminal
Power supply terminal.
Output at this terminal are the custom code (16bits) remote control code input to REMOTE
IN, data code (8bits), and the serial code (12bits) that has been converted corresponding to
the decoded data code (8bits)
When the player PLAY/REEJECT is input, a high pulse of 200ms is output.
SYS OUT
PHONO
VOL DOWN When the volume DOWN code is input, a high pulse of 120ms is output.
VOL UP
VOLIND
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When the volume UP code is input, a high pulse of 120ms is output.
POBO | VOL IND During the output of VOLUME UP/DOWN, a pulse ([T LT JT LTJ= 250ms) is output.
(Not used.)
POB1 | RECEI This is the display output for remote control reception. Output is low when decoded code is
being recieved.
POB2 “BY STAND-BY indication terminal.
[16 [Va [GND
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Q133
PLL SYNTHESIZER
ANO CONTROLLER
RESET
preset LRESET
AMIOK
BANDI
BANDO
xT2
xT I
Region [Range space
| Europe _ |87.50-108.00MHz |SOkEiz
SOkHz
100kHz
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TERMINAL DESCRIPTION
sa
ppage of electric current.
SYS OUT/ {System code output terminal."L"when active.
SYS EN Initializing input terminal when the power turns on.
a
"L" when stereo broadcast.
| 9 |sysIN | System code input terminal."H" when active.
Broadcast detection input terminal."L" when active.
Control the stop of auto tuning and output TU MUT(#19).
NOISE _ [Noise detection input terminal.Not used.
| 12 [PROTECT
PHONO
| Notused, tt C(‘“‘“‘CSOC*C*C‘*zC
| 17. {MODE | Initializing input terminal for operation mode setting.
Speaker relay control output terminal.
Key scan input terminals.
"H" when active.
Connect to the terminal CE of PLL IC (LM7001 0133).
Connect to the terminal CL of PLL IC and analogue switch.
Connect to the terminals DATA of PLL IC and analogue switch.
SEL Analog switch control output terminal.
Connect to the terminal SEL of analogue switch
7823 Q324
31 Connect to the 4.19MHz ceramic oscillator.
Ceramic oscillator connection terminal for sub system clock.
| 34 s[xT2 Not used.
Initializing input terminal for region setting of FM band.
| 48
p49 | |Notused
| 50 {sn
[51 Isms Segment output terminals."H" when active.
| 52 isi
53
S.TONE _|SELECTIVE TONE control output terminal.Not used.
| 59 isi
| 60 {sh | Segment and key scan output terminals.
| 61 |ss | "H" when active.
| 2 ise
| 63 ise
| 64__|vDD __[Powersupplyterminal(+5V)
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TX-7900/TX-7920
LA1266(FM IF and AM radio system)
Fa 1F IF AMP IF 10. 7MHz
am us ae be iF IN STOP ouT IN Yee
——— 1 2
——— —_—_—. a a —_— ——
1 |
i
I F IF NATE: aie OsT
FM IF AMP aaa —o—12 FM
BUEEES BUFFER|_ DETECTOR AMP OUT
T zi
H H
1 i
Ss
At IF 18——~ 98
IN { CURVE
AM IF | 20 —
our | al
RF im
NARROW | LED
AM OSC BUFFER REG Ss A. G. C 8
METER METER DRIVER
| q |
|
$e | Gene | Jee |
7
'
| — 15 aN
cine OUT
Osc GND
* f ouT
AN7470(Stereo decoder)
115 |
————
PHASE PILOT STEREO SW a
76 k PRESENCE
DETECTOR
Hz
DAIVe
*
eh
J
a
er
ey
To
i
bivicen
ed
piviDeR
yA it ne
oIviDeR
STEREO
LB1630(Motor driver)
(MODEL TX-7920)
Voutl Vout2
TRUTH TABLE
~14—

TX-7900/TX-7920
FIPSBTM8(Fluorescent tube)
FM Stereo Indicator Tape-2 Monitor Indicator
Tuned Indicators Memory Indicator
FM Muting On/Off indicator
Y emony
1 aupio mute
‘ae HT Ra enim
PL ae ‘CT es
D2; D1
Preset Station Display
Audio Muting Indicator
(TX-902 only)
APR
RF STEREO
MODE MODE
os
APR system indicators
Classified Memory Display
coe

TX-7900/TX-7920
LC7823/LC7823N(Analog switch)
Lto j = oo | oR!
vel gg [Fg bon
Lcomt 0 ; © RCOMI Serial Data Composition
uot —g Same le
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LC7823-N
Polat
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Res > SHFT REGSTER F <i | oes
[5,26 [TAPE-1 PB
LCOM2,RCOM2
Off when the input selector is TAPE-2.
TAPE-2 PB On when the input selector is TAPE-2.
LCOM3,RCOM3 {Common terminal.
LCOM4,RCOM4
Negative power supply terminal.(-15V)
Chip enable terminal.Connect to the terminal FUNC of the microprocessor.
| wu |p | Serial data input terminal.Connect to the terminal DATA of the microprocessor.
Serial clock terminal.Connect to the terminal CL of the microprocessor.
[16 [Vss_ | Ground terminal.
Select terminal.
| 18 |RES {Reset terminal.
[19 [VDD __| Power supply terminal.(45V
4 PC1225H(Power amplifier driver) NJM4558D-X(Operation amplifier)
—~16—

PACKING VIEW
TX-7920
REF.NO. PART NO.
1 29052331 Y
29052332Y
29091440AY
29091441AY
29100034A
282301
29110071
261504
Accessary bag ass'y
29341685Y
29100097
292112Y
232140
29365020E
29100094A.
3010165Y
24140223Y
2010200
oI nn & WwW WV
DESCIRPION
Master carton box <B>
Master carton box <S>
Pad L
Pad R
850 X650,Styrene bag
Sealing hook
Damplon tape
Adhesive tape
Instruction manual
350 X 250,Styrene bag
FM antenna
NMA-3057,AM loop antenna
Warranty card
Styrene bag for warranty card
UM-3,Two batteries
RC-223S,Remote control unit
Cord RI
-~17—-
TX-7900
REF.NO.
2
3
4
5
6
7
8
NOTE:
TX-7900/TX-7920
PART NO. DESCIRPION
29052334Y Master carton box <B>
29052335Y Master carton box <S>
29091440AY Pad L
29091441AY Pad R
29100034A 850 X650,Styrene bag
282301 Sealing hook
29110071 Damplon tape
261504 Adhesive tape
Accessary bag ass'y
29341685Y Instruction manual
29100097 350 X250,Styrene bag
292112Y FM antenna
232140 NMA-3057,AM loop antenna
29365020E Warranty card
291000944 Styrene bag for warranty card
<B>:Black model only
<S>:Silver model only

TX-7900/TX-7920
ADJUSTMENT PROCEDURES
Preparation
1.Input
FM mono:1kHz,75kHz devi.,60dB/ » V
FM stereo: 1kHz,75kHz devi.,60dB/ nu V
Pilot signal 19kHz 7.5kHz devi.
AM:400Hz 30% mod.
2.Outputs
Connect the non-inductive type resistors of 8 ohms
to the speaker terminals A unless otherwise noted.
3.Standard Knob Position
VOLUME ii vtisdessscssescdsescsseessenveas Maximum
BASS/TREBLE/BALANCE............ Center
MUTING/LOUDNES.G.................. Off
INPUT SELECTOR...................06 CD
SPEAKERS... ccc cecceeseceeseceneees A
Confirming Operation
1.Protection circuit
a. Speaker relay
The speaker relay turns on after the power switch turned on for 5 minutes.
The speaker relay turns off immediately after the power switch turns off.
b. Over-voltage confirmation
The speaker relay is off immeditely after DC voltage + 6V is applied to the terminal CD.
Amplifier section
Idling Current Adjustment
Connect the DC voltmeter to the terminals LID(RID) and CT on the power amplifier pc board.
Adjust the semi-fixed resistor R511(R512) so that the indication of voltmeter is 5+0.5mV.
Note:(_ ):Right channel
R512 =) 9S R511
o LID
0 VCT
RID o
VCT o
—~18—
POWER AMPLIFIER PC BOARD
SOLDERING SID!

FM section
Item Step | Connection of FM SG output Stereo modu- Tuned Output indicator Adjustment Adjust for Remarks
instrument lator output frequency point
DC voltmeter L101 0+20mV Set the FM mode
99.1MHz switch to MONO. Repeat
Fig. 1 1kHz,75kHz devi. 99.1MHz the steps 1 and 2 util
65dBf(60dB) Distortion L102 no further adjustment
analyzer in necessary.
a SS ew : 2 =
1kHz,75kHz devi. 99.1MHz R201 19kHz+10Hz
Distortion IF on
99.1MHz
analyzer front end
65d Bf(60dB)
Lech. 1kHz Rch. AC voltmeter
99.1MHz R202
Rch. 1kHz Lch. AC voltmeter
99.1IMHz
switch to AUTO.
99.1MHz
Ext. modulation
65d Bf(60dB)
99.1MHz
Ext. modulation
65d Bf(60dB)
99.1MHz
1kHz, 75kHz devi.
17. 2dBéf (12dB)
Maximum and same
separation
Tuned
TUNED
indicator R101
99. 1MHz
1kHz, 75kHz devi.
16. 2dBf£ (11dB)
indicator
level
AM section
Step AM SG
output
1
522kHz
|Digital
DC
|
OSC
coil
—‘|1.5V+0.1V
Reference
specifications
.
voltmeter
on
RF
block
Tuned
voltage
AM_
522kHz
1.5
+0.4V
(L151)
(Connet
Digital
1611kHz
7.5
+0.5V
DC
voltmeter
to
FM
87.50MHz
2.0
+0.5V
603kHz,60dB/m
|
603kHz
AC
RF
coil
test
point
TP-6)
108.0MHz
7.5
+0.5V
on
RF
block
400Hz
30%
mod.
voltmeter
(L151)
Muting
width
35 +
10kHz
990kHz, 60dB/m 990kHz ae
400Hz 30% mod. Sal nebeE
AM
signal
generator
Output
terminal
antenna
terminal AM
AM
AM LOOP TpP-6
E
LOOP antenna
Digital
oc
voltmeter
—~19—
Muting level FM 12 + 3dB
Auto stop level AM Less than 68dB/m
FM Less than 20dBu
Stereo indicator level 14 + 4dBu
TX-7900/TX-7920
OUTPUT
terminal
FM signal Distortion
generator analyzer
Antenna Terminals
terminal Tp TP-2
oc
voltmeter
(Fig. 1)
Antenna
terminal
TP-4
FM signal = Frequency
generator counter
E
Use the high impedance probe. (10:1)
(Fig. 2)
Terminal
Antenna OUTPUT
EXTumode terminal terminal
Stereo FM signal AC
modulator generator Unit voltmeter
Terminal
TP.4
Frequency Distortion
counter analyzer
<Fig.3>
Adjustment point.
—20—

TX-7900/TX-7920 TX-7900/TX-7920
PRINTED
CIRCUIT
BOARD
VIEW
FROM
BOTTOM
SIDE
POWER AMPLIFIER
CIRCUIT PC BOARD
cs
|
-
DISPLAY
CIRCUIT
PC
BOARD
a