VC-MH742HM (serv.man20). Electrical adjustments - Sharp VCR Service Manual (repair manual)

vc-mh742hm (serv.man20) service manual
Model
VC-MH742HM (serv.man20)
Pages
3 Few pages! See other manuals at the bottom of the first or last page.
Size
26.04 KB
Type
PDF
Document
Service Manual
Brand
Device
VCR / Electrical adjustments
File
vc-mh742hm-sm20.pdf
Date

Read Sharp VC-MH742HM (serv.man20) Service Manual online

28
VC-M332HM
VC-MH742HM
5. ELECTRICAL ADJUSTMENT
Notes:
• Before the adjustment:
Electrical adjustments discussed here are often required after replacement of electronic components and mechani-
cal parts such as video heads.
Check that the mechanism and all electric components are in good working condition prior to the adjustments,
otherwise adjustments can not be completed.
• Instruments required:
Colour TV monitor
Dual-trace oscilloscope
         Alignment tape (VROCPSV)
Blank video cassette tape
DC voltmeter
Screwdriver for adjustment
Servicing precations
When the IC705 (E
2
PROM) has been replaced, make the following reprogramming. Depending on models, the IC705
(E
2
PROM) has been factry-adjusted for it’s memory function.
It’s therefore necessary to reprogram the memory function for the model in question.
Note that the servo circuit requires readjustments for the head switching point, slow and still modes.
• Location of controls and test points
Figure 5-1.
29
VC-M332HM
VC-MH742HM
SERVO CIRCUIT ADJUSTMENT
ADJUSTMENT OF HEAD SWITCHING POINT
Measuring
instrument
Mode
Cassette
Dual-trace oscilloscope
Colour TV monitor
Playback
Alignment tape (VROCPSV)
Test point
Pin(2) of P201 (H.SW.P.) to CH-1,
VIDEO OUT jack to CH-2
(CH-1 trigger slope switch at (+),
Internal trigger at CH-1 side.)
Specification
6.5 
±
 0.5H (lines)
1. Remove the front panel and play the alignment tape.
(VROCPSV)
2. Press the PLAY button.
(Playback picture on the monitor screen.)
3. Make for a moment short-circuit P802, located at the
front side on the main PWB.
Be sure that all the fluorescent display tubes light up
into the TEST mode.(See Note below)
Be sure the "PLAY" appears in the fluorescent display
tubes flashing (about 1Hz) into the auto PG adjust-
ment operating.
Note:
When the manual PG adjustment, obseve the wave-
form with an oscilloscope and make adjustment FF or
REW button so that the specification.
4. Stop the "PLAY" appears in the flashing of fluorescent
display tubes at adjusted.
5. Press the STOP button in the return to normal mode.
6. Make this checking of waveform on the oscilloscope
screen be as shown in Figure 5-2. just after the head
switching point have been adjusted.
Note:
1
Set-up of TEST mode.
When the adjustment of HEAD SWITCHING POINT,
AUTO TRACKING function is invalid.
2
When the cassette housing control ass’y is removed,
set-up of mechanism operating mode.
1) Replug the AC power cord it a few minutes later.
2) Make a short-circuit P801 located at the front side on
the main PWB, and press both tracking control button
at the same time to set the tracking in center.
3) AC power cord is plugged in.
4) You can mechanism operatig mode, Replug the AC
power cord a few minutes later.
Measuring
instrument
Mode
Cassette
Colour TV monitor
Playback
Self-recorded tape
(SP/LP mode)(See Note below)
Control
Tracking control buttons (+) or (–)
Specification
Minimized noise on
monitor screen
ADJUSTMENT OF PAL SYSTEM SP/LP
SLOW TRACKING PRESET
1. Have the unit to receive a good TV broadcast or feed
a video signal to the VIDEO IN jack. (See note 
2
below)
2. Set the tape speed in SP mode by using the remote
control and record the signal on tape.
3. Rewind and play the tape where signal was recorded
in above step.
4. Press the SLOW button on the remote control, and
playback the recorded portion in the slow mode.
5. Make for a moment short-ciucuit  P802, located at the
front side on the main PWB.
Be sure that all the fluorescent display tubes light up
into the TEST mode.
6. Look at the monitor screen and adjust the (+) or (–)
TRACKING buttons so that the there is noise disap-
pears from the screen.
7. Press the STOP button to return to normal mode.
8. Play the tape a few seconds then press the SLOW
button again and make sure there is on noise in the
screen.(For the LP mode put adjustment at the same
adjustmet way as SP mode.)
Notes:
1
Self-recorded tape means a cassette whose pro-
gram was recorded by the unit being adjusted.
2
The TV program will not be recorded if RCA or 21pin
plugs are pluged in to the AUDIO/VIDEO input
terminals.
6.5
±
0.5H (lines)
CH-1: 1V/div 50
µ
s/div
CH-2: 2V/div 50
µ
s/div
V-sync.
CH-1
HEAD
SWITCHING
PULSE
CH-2
VIDEO OUT
Figure 5-2.
30
VC-M332HM
VC-MH742HM
Measuring
instrument
Mode
Test point
Colour TV monitor
DV voltmeter
RF signal at 40CH(by VHF
signal generator)
Pin(2)(Sig.) of P1501.
Pin(4)(GND.) of P1501.
Control
R1626 RF AGC control
Specification
3.9 
±
 0.2V
1.Receive the 40 channel signal (colour bar signal at
   87.5% modulated.) at input field strength: 56dB
µ
 of
   antenna terminal.
2.Connect a DC voltmeter to test point shown in table.
3.Look the voltmerter and adjust R1626 so that the
   voltage be specified.
Measuring
instrument
Mode
Test point
Colour TV monitor
DV voltmeter
Control
T1601 VCO control
Specification
2.5
±
0.2V
RF signal at 40CH(by VHF
signal generator)
Pin(1)(Sig.) of P1501.
Pin(4)(GND.) of P1501.
ADJUSTMENT OF RF AGC ADJUSTMENT
Note:
When power is turned on, tune in to station in the test
mode.
1.Receive the 40 channel signal(colour bar signal at
   87.5% modulated.) at input field strength: 70dB
µ
 of
   antenna terminal.
2.Connect a DC voltmeter to test point shown in table.
3.Look the voltmerter and adjust T1601 so that the
   voltage be specified.
ADJUSTMENT OF VCO CIRCUIT
Measuring
instrument
Mode
Cassette
Colour TV monitor
Playback still
Self-recorded tape (SP mode)
(See Note below 
2
)
Control
Tracking control buttons (+) or (–)
Specification
No vertical jitter of picture
ADJUSTMENT OF PAL SYSTEM FV(False
Vertical Sync) OF STILL PICTURE
1. Play a cassette which was recorded by the unit in SP
mode.
2. Press the PAUSE/STILL button to freeze the picture.
3. Look at the monitor screen and adjust (+) or (–)
TRACKING buttons so that the vertical jitter of the
picture to be minimized.
4. Play and freeze the self-recorded tape in SP mode
and make sure vertical jitter of the picture is not
noticeable.(For the LP mode put adjustment at the
same adjustment way as SP mode.)
Note:
1
2
Self-recorded tape is a cassette whose program was
recorded by the unit being adjusted.
Page of 3
Display

Download Sharp VC-MH742HM (serv.man20) Service Manual (Repair Manual)

Here you can read online and download Sharp VC-MH742HM (serv.man20) Service Manual in PDF. VC-MH742HM (serv.man20) service manual will guide through the process and help you recover, restore, fix, disassemble and repair Sharp VC-MH742HM (serv.man20) VCR. Information contained in service manuals typically includes schematics / circuit diagrams, wiring diagrams, block diagrams, printed wiring boards, exploded views, parts list, disassembly / assembly, pcb.