Sony DXA-H2750 User manual

SERVICE
MANUAL
This set is the Amplifier,
cassette deck section
in FH-E705C, MHC-2750.
SONY-06187
DXA-H2790
US Model
Canadian Model
AEP Model
UK Model
E Model
Australian Model
Tourist Model
Model
Name
Using
Similar
Mechanism]
TC-H2700/H3700
Tape
Transport
Mechanism
DECK
A|
TCM-190RA13A
Type
:
DECK B| TCM-19ORB22A
SPECIFICATIONS
Amplifier Section
Continuous RMS power output
US, CND model:
45 + 45 watts (6 ohms at
1 kHz, 5% THD)
E, EA, AUS, TR model:
40. + 40 watts (6 ohms at
1 kHz, 5% THD)
AEP, UK, G, IT model:
35. +35 watts (6 ohms at
1 kHz, DIN)
Music power output
AEP, UK, G, IT model:
60 + 60 watts (6 ohms at
1 kHz, 10% THD)
Peak music power output
£, EA, AUS, TR model:
400 watts
inputs DAT IN (phono jacks):
sensitivity 450 mV,
impedance 47 kilohms
AEP, UK, G, IT model:
PHONO IN (phono jacks):
sensitivity 5 mV,
impedance 47 kilohms
Except AEP, UK, G, IT model:
VIDEO IN (phono jacks):
sensitivity 450 mV,
impedance 47 kilohms
Outputs HEADPHONES
(stereo minijack):
accepts headphones of
8 ohms or more
SPEAKERS:
accepts speakers of 6 to
16 ohms
Cassette Deck Section
Recording system 4-track 2-channel stereo
Frequency response (DOLBY NR OFF)
40 — 13,000 Hz (+3 dB),
using TYPE | cassette
(Sony HF-S)
40 — 14,000 Hz (+3 dB),
using TYPE ii cassette
40 — 15,000 Hz (+3 dB),
using TYPE IV cassette
Wow and flutter 0.1% WRMS +0.3% (DIN)
Design and specifications subject to change
without notice.
STEREO
CASSETTE
DECK
AMPLIFIER
ONY.

DXA-H2750 |
SAFETY CHECK-OUT
After correcting the original service problem,
perform the following safety check before releasing
the set to the customer:
Check theantenna terminals, metal trim, “metallized”
knobs, screws, and all other exposed metal parts for
AC leakage. Check leakage as described below.
LEAKAGE TEST
The AC leakage from any exposed metal part to
earth ground and from ail exposed metal parts to any
exposed metal part having a return to chassis, must
not exceed 0.5mA (500 microampers). Leakage
current can be measured by any one of three
methods.
1. A commercial leakage tester, such as the
Simpson 229 or RCA WT-540A. Follow the
manufacturers’ instructions to use these instru-
ments.
Ne
A battery-operated AC milliammeter. The Data
Precision 245 digital multimeter is suitable for
this job.
3. Measuring the voltage drop across a resistor by
means of a VOM or battery-operated AC volt-
meter. The “limit” indication is 0.75V, so
analog meters must have an accurate low-
voltage scale. The Simpson 250 and Sanwa
SH-63Trd are examples of a passive VOM that
is suitable. Nearly all battery operated digital
multimeters that have a 2V AC range are
suitable. (See Fig. A)
To Exposed Metal
Parts on Set
AC
0.15 nF voltmeter
jo 3) (0.75 V)
= Earth Ground
Fig. A. Using an AC voltmeter to check AC leakage.
MODEL IDENTIFICATION
— Model Number Label —
SONY movetno. pxa-H2750
STEREO CASSETTE DECK AMPLIFIER
WML
US model: AC: 120V 60Hz 105W
CND model: AC: 120V 60Hz 115W
AEP model: AC: 220-—230V~50/60Hz
UK model: AC: 240V~50Hz
E, EA, TR model: AC: 120/220/230~-240V~50/60Hz 110W
G, 1T model: AC: 220—230V~50Hz
AUS model: AC: 240V~50Hz 110W
@CND: Canadian model
e@ AUS: Australian model
eG: Germany model
elT: italian model
@EA: Saudi Arabia model
e@TR: Tourist model
SAFETY-RELATED COMPONENT WARNING!!
COMPONENTS IDENTIFIED BY MARK A OR DOTTED
LINE WITH MARK A ON THE SCHEMATIC DIAGRAMS
AND IN THE PARTS LIST ARE CRITICAL TO SAFE
OPERATION. REPLACE THESE COMPONENTS WITH
SONY PARTS WHOSE PART NUMBERS APPEAR AS
SHOWN IN THIS MANUAL OR IN SUPPLEMENTS PUB-
LISHED BY SONY.
ATTENTION AU COMPOSANT AYANT RAPPORT
A LA SECURITE!
LES COMPOSANTS IDENTIFIES PAR UNE MARQUE /(\
SUR LES DIAGRAMMES SCHEMATIQUES ET LA LISTE
DES PIECES SONT CRITIQUES POUR LA SECURITE
DE FONCTIONNEMENT. NE REMPLACER CES CCM-
POSANTS QUE PAR DES PIECES SONY DONT LES
NUMEROS SONT DONNES DANS CE MANUEL 9U
DANS LES SUPPLEMENTS PUBLIES PAR SONY.

| DXA-H2750
TABLE OF CONTENTS
Section Title Page Section ’ Title Page
1. GENERAL 5. DIAGRAMS
j-l. Part Identification .............-.. 02. e eee ee ee eee ee 3 5-1. Semiconductor Lead Layouts ................660. 13
5-2. Ciaucuit Boards Location ....................006- 14
2. DISASSEMBLY 5-3. Printed Wiring Boards —Deck Section—.......... 16
2-1. Front Panel ............... cece cece e eee eee eaee 4 5-4. Schematic Diagram —Deck Section— ............ 19
2-2. Control Board, HP Board .....................05. 4 5-5. Schematic Diagram —Main Section— ............ 24
2-3. Cassette Lid Assy ............ cece eee e centre eee 5 5-6. Printed Wiring Boards —Main Section— ........ 29
2:4, MD Bl0ck® occ cen secvanivdeae ern eaienldse ai aciiens 5 5-7. Printed Wiring Boards —-Panel Section— ........ 34
2:5.. “Back Panel: tee .cneia ce cexiwints alee evse Uieeet e 6 5-8. Schematic Diagram —Panel Section— ............ 37
2-6. Power Transformer .............. cece e scence eeees 6
2-7. TC Main Board ............0cc ccc ce cece ne ee ences 7 6. EXPLODED VIEWS
2-8. Joint (Upper) ........... 0. cee cece e eee eens 7 6-1. Cabinet Section ............. sche NE dep Wa ae Bh ch ane 42
2-9. Capstan/Reel Motor .............-.. sees eee eee eee 8 6-2. Chassis Section............0ccc cece ee eee n cea eeeee 43
2-10. Head Base ASSY........... sce e eee e ee eee eee eens 8 6-3. Cassette Holder Section................. cee eee 44
6-4. Mechanism Deck Section 1] .................00005 45
3. MECHAINICAL ADJUSTMENTS .................. 9 6-5. Mechanism Deck Section 2 ..............0:e sees 46
4. ELECTRICAL ADJUSTMENTS .................... 9 7. ELECTRICAL PARTS LIST ...................... 47
LD CD ALD DAL AED AP AD EP AED MEE AED AED E> D> AER ECD» AED AD ALD AEP ED ARES» RE E> NEED D> AED» AEE: A> AED» E> AEG AE D> ERED: AEG» ID AED AED AEE AGS Ds AED AE AR AE AED ALES AED ARORA AS
SECTION 1
GENERAL
1-1. -_PARTS IDENTIFICATIONS This section is extracted from
instruction manual.
(1) HEADPHONES jack (stereo minijack)
[2] SYSTEM POWER switch and STANDBY
indicator
The indicator remains lit as long as the
AC power cord is connected to a wall
outlet.
[3] DISPLAY button @
[4] DIRECT button and indicator @
(5) FUNCTION button and function
indicators @ @
[6] PRESET button @
VOLUME control @
TOTAL EFFECT CONTROL
—/+ buttons @
[8] Cassette holder (Deck B)
EJECT & button (Deck 8B)
[13] Tape operation buttons (for Deck 8)
Q: Stop button
(>: Forward play button and indicator
<]: Reverse play button and indicator
<4 p>: Fast winding buttons
PAUSE [f: button and indicator
REC @: button and indicator
[12] DOLBY NR (Dolby Noise Reduction)
switch @
[3] CD SYNCHRO button @ @
TAPE DUBBING buttons @
NORMAL SPEED button
HIGH SPEED button
[is] DIRECTION mode selector @ @
Tape operation buttons (for Deck A)
©: Stop button
>: Forward play button and indicator
<j: Reverse play button and indicator
<4 p>: Fast winding buttons
EJECT & button (Deck A)
Cassette holder (Deck A)

DXA-H2750 |
Note
:
Follow
the
disassembly
procedure
in
the
numerical
order
given.
SECTION 2
DISASSEMBLY
2-1. FRONT PANEL
@ Connector CN956
N80
te } © Connectors
CN953
@ Connectors }CN109
CN104
O Claws
@ BVTP 2.6x8
2-2. CONTROL BOARD, HP BOARD
@ CN505
BVTT 3X6
Control board
@ Knob (VOL) assy

2-3. CASSETTE LID ASSY
2-4. MD BLOCK
BVTP 2.6X8
| DXA-H2750

DXA-H2750 |
2-5. BACK PANEL
BD CN952
(US, Canadian)
> BVTP 3X10
BVTP 3x10
@ Back panel
D BVTP 3x10
2-6. POWER TRANSFORMER
@ Bracket (heat sink)
B Heat sink
@ BVTT 3x6
Power tranfomer

2-7. TC MAIN BOARD
@TC main board
@CN601
@ CN603
2-8. JOINT (UPPER)
@ BVTP 2.6x8
@ Joint (upper) @ BVTP 2.6x8
| DXA-H2750

DXA-H2750 |
2-9. CAPSTAN/REEL MOTOR @ PTPWH 2x23
@ fitting base
@ Claws @ When installing, pull
the FR belt and put
arround claws.
© When installing, pull the capstan
belt and put arround claws.
@ connectors
@ capstan motor ground plate’
connector
@B2.6x3
@ Claws @ MD-A board
MD-B board
@ reet motor
belt (FR)
@ P2.6X2.8
2-10. HEAD BASE ASSY
@ Claw
@ head basd assy
os @ torsion spring
hy: 9:
@ lever (pinch lever REV) assy lever (pinch lever FWD) assy
—8—

SECTION 3
MECHANICAL ADJUSTMENTS
PRECAUTION
1. Clean the following parts with a denatured alcoholmois-
tened swad:
record/playback head
erase head
pinch roller
rubber belts
capstan idlers
2. Demagnetize the record/playback head with a head
demagnetizer.
(Head demagnetizer do not approach for the erase head.)
3. Do not use a magnetized screwdriver for the adjustment.
4.
After
the
adjustments,
apply
suitable
locking
compound
to the parts adjusted. .
5. The adjustments should be perfomed with the rated
power supply voltage unless otherwise noted.
Torque Measurement
Meter reading
30 to 65g * cm
CQ-1020 (0.42 to 0.90 02 « inch)
Forward 1 to 6g*cm
CR 1ee (0.014 to 0.0802 + inch)
30 to 65g * cm
©0-102RC (0.42 to 0.9002 « inch)
Reverse 1 to 6g * cm
back tension €Q-102RC (0.014 to 0.0802 * inch)
Forward,
70
to
120g
>
cm
Reverse
€Q-201B
(0.98
to
1.67
oz
«
inch)
| DXA-H2750
SECTION 4
ELECTRICAL ADJUSTMENTS
PRECAUTION
1. The adjustment should be performed in the publication.
(Be sure to make playback adjustment at first.)
2. The adjustment and measurement should be performed
for both L-CH and R-CH.
@ Switch position
DOLBY NR switch: OFF
3. Perior to electrical adjustments, short the connector
TP401 (test mode).
Test Tape
[Tape | __—Contents [| Use
P-4-A100 10kHz, —10dB Azimuth Adjustment
P-4-L300 315Hz, 0dB Level Adjustment
WS-48B 3kHz, 0dB Tape Speed Adjustment
Record/Playback Head Azimuth Adjustment
Procedure :
1. Forward Playback Mode
test tape
P-4-A100
(10kHz, —10dB)
TP201 (LINE OUT)
2. Turn the adjustment screw for the maximum output
levels. If these levels do notmatch, turn the adjustment
screw until both of output levels match together within
1dB.
L-CH
peak
within 1dB
R-CH
screw Peak
position
L-CH RCH ~ —
peak peak er

DXA-H2750 |
3. Playback Mode
test tape
P-4-A100
(10kHz, —10dB)
L-CH 47kQ
in phase 45°
good
4. Change the reverse playback mode and repeat the steps
1 to 3.
5. After the adjustment, lock the adjustment screw with
suitable locking compound.
Adjustment Location : —record/playback head—
azimuth
cover
+
Removing
the
azimuth
cover.
§
Unlock
the
stoppers
of
the
azimuth
cover
using
a
L-shaped
wrench
in
order
to
adjust.
Tape Speed Adjustment
Procedure :
—Forward Playback Mode—
test tape
WS-48B
(3kHz, 0dB) frequency counter
TP201 (LINE OUT)
Perform high speed adjustment before normal speed adjust-
ment.
(High speed adjustment)
1. Turn on the power and put the deck A into the FWD
mode.
2. Press the HIGH SPEED switch.
3. Adjust RV72A (H) of the deck A so that a reading on the
frequency counter meets the adjustment value.
4, Adjust the RV72B (H) of deck B performing steps 1 to 3
as deck A.
(Norma! speed adjustment)
1. Put the set into the FWD playback mode.
2. Press the NORMAL SPEED switch.
3. At this time, adjust RV71A (L) of the deck A and RV71B
(L) of the deck B so that a reading on the frequency
counter meets the adjustment value.
Adjustment Limits :
Frequency Counter Reading
6,000 + 20Hz
3,000 + 10Hz
Frequency difference between the beginning and the ead of
the tape should be within 3%.
Frequency difference between deck A and deck B the begin-
ning of the tape should be within 1.5%.
Adjustment Location: MD-A Board, MD-B Board