Sharp VC-MH75HM User manual

1
VC-MH75HM
VIDEO CASSETTE RECORDER
SERVICE MANUAL
SHARP CORPORATION
In the interests of user-safety (Required by safety regulations in some
countries) the set should be restored to its original condition and only parts
identical to those specified be used.
VC-MH75HM
MODEL
CONTENTS
Page
1. SPECIFICATIONS................................................................................................................. 3
2. DISASSEMBLY AND REASSEMBLY ................................................................................... 4
3. FUNCTION OF MAJOR MECHANICAL PARTS................................................................... 6
4. ADJUSTMENT, REPLACEMENT AND ASSEMBLY OF MECHANICAL UNITS .................. 8
5. ELECTRICAL ADJUSTMENT ............................................................................................. 27
6. MECHANISM OPERATION FLOWCHART AND TROUBLESHOOTING GUIDE............... 34
7. ELECTRICAL TROUBLESHOOTING ................................................................................. 40
8. BLOCK DIAGRAM............................................................................................................... 56
9. SCHEMATIC DIAGRAM AND PWB FOIL PATTERN ......................................................... 64
10. REPLACEMENT PARTS LIST ............................................................................................ 82
11. EXPLODED VIEW OF MECHANISM PARTS..................................................................... 90
12. PACKING OF THE SET ...................................................................................................... 94
S23X7VC-MH75H

4
VC-MH75HM
8
A
D
7
7
9
1
C
242
4
5
B
E
B
D
A
C
6
D
FRONT PANEL
B
3
3
6
E
TOP CABINET
TOP CABINET
FIX ANGLE
MAIN FRAME
OPERATION PWB
ANTENNA
TERMINAL
COVER
EUR-TERM PWB
MAIN PWB
MECHANISM
CHASSIS
CASSETTE
HOUSING
CONTROL
F
F
2. DISASSEMBLY AND REASSEMBLY
2-1 DISASSEMBLY OF MAJOR BLOCKS
TOP CABINET : Remove 2 screws 1.
FRONT PANEL : Remove 2 screws 2and 7 clips 3.
MECHANISM/ : Remove 2 screw 4, 1 screw 5.
MAIN PWB Remove2screws6and2screws7
with antenna terminal cover. Remove
1 screw 9. Remove 1 screw 8 with
top cabinet fix angle.

6
VC-MH75HM
3. FUNCTION OF MAJOR MECHANICAL PARTS (TOP VIEW)
No. Function No. Function
1 Full erase head
2 Supply pole base ass’y
3 Tension arm
4 Idler wheel ass’y
5 Open guide
6 Supply reel disk
7 Supply main brake
8 Take-up main brake
9 Pinch drive cam
10 A/C head ass’y
11 Reverse guide lever ass’y
12 Reel relay gear
13 Take-up reel disk
14 Pinch roller lever ass’y
15 Drum ass'y
16 Loading motor block
17 Drum driver motor
18 Take-up pole base ass'y
17 15
11
5
9
14
12
8
16
13
4
6
2
7
3
1
18 10

7
VC-MH75HM
FUNCTION OF MAJOR MECHANICAL PARTS (BOTTOM VIEW)
No. Function No. Function
19 Syncro Gear
20 Master cam
21 Capstan D.D. motor
22 Reel belt
23 Clutch lever
24 Limiter pulley ass’y
25 Shifter
25
24
21
22
19
20
23

8
VC-MH75HM
VROCPSV CK
11. JiGHMEC-M005 CK
10. JiGDRiVER-6 BM
9. JiGDRiVERH-4 AP
4. Torque Driver JiGTD1200 CB
4. ADJUSTMENT, REPLACEMENT AND ASSEMBLY OF MECHANICAL UNITS
The explanation given below relates to the on-site general service (field service) but it does not relates to the adjustment
and replacement which need high-grade equipment, jigs and skill. For example, the drum assembling, replacement and
adjustment service must be performed by the person who have finished the technical courses.
4-1 MECHANISM CONFIRMATION ADJUSTMENT JIG
So as to perform completely the mechanism adjustment prepare the following special jigs. So as to maintain the initial
performance of the machine the maintenance and check are necessary. Utmost care must be taken so that the tape is
not damaged. If adjustment needs any jig, be sure to use the required jig.
JiGTG1200 CN
JiGMP0001 BY
1. Torque Cassette Meter JiGVHT-063 CZ
No. Jig ltem Part No. Code Configuration Remarks
JiGTG0090 CM
3. Torque Gauge Head JiGTH0006 AW
JiGRH0002 BR
JiGSG2000 BS
JiGSG0300 BF
7. JiGADP003 BK
Tension Gauge
These Jigs are used for checking
and adjusting the reel disk height.
Whenfixinganyparttothethreaded
hole using resin with screw, use the
jig. (Specified torque 5 kg)
Thiscassettetorquemeterisusedforcheck-
ing and adjusting the torque of take-up for
measuring tape back tension.
These Jigs are used for checking
and adjusting the torque of take-up
and supply reel disks.
Master Plane Jig and
Reel Disk Height
Adjusting Jig
Pinch pressing force
measuring jig
This Jig is used with the tension
gauge.Rotarytransformerclearance
adjusting jig.
There are two gauges used for the
tension measurements, 300 g and
2.0 kg.
Thesetapes are especiallyused for
electrical fine adjustment.
Video Audio HiFi Audio Track
625 Monoscope 7k — 49µm
PAL Colour Bar 1k — 49µm
This screwdriver is used for adjusting the
guide roller height.
For X value adjustment
This Jig is used for adjustment
of tension pole.
X value adjustment
gear driver
Tension Pole
Adjustment Driver
2. Torque Gauge
6.
5.
8. Alignment Tape
Guide roller height
adjustment driver

9
VC-MH75HM
4-2 MAINTENANCE CHECK ITEMS AND EXECUTION TIME
Perform the maintenance with the regular intervals as follows so as to maintain the quality of machine.
NOTE : Part replacement. : Cleaning : Apply grease
<Specified> Cleaning liquid Industrial ethyl alcohol
* This mechanism does not need electric adjustment with variable resistor. Check parts. If any deviation is found,
clean or replace parts.
Maintained
Parts Remarks
500
hrs. 1000 hrs. 1500 hrs. 2000 hrs. Possible symptom
encountered
Guide roller ass’y
Sup guide shaft
Reverse guide
Slant pole on pole base
Full erase head
A/C head
Upper and lower drum ass’y
Capstan D.D. motor
Pinch roller
Reel belt
Tension band ass’y
Loading motor
Idler ass’y
Limiter pulley
Supply/take-up main brake levers
Colour and beating
Small sound or sound
distortion
Poor S/N ratio, no colour
Poor flatness of the
envelope with alignment
tape
No tape running,
uneven colour
No tape running, tape
slack
No tape running, tape
slack, no fast forward/
rewind motion
Lateral noises Head
occasionally blocked
Abnormal rotation or significant
vibration requires replacement.
Clean tape contact part with the
specified cleaning liquid.
Clean tape contact area with the
specified cleaning liquid.
Clean rubber and rubber contact
area with the specified cleaning
liquid.
Screen swaying
Cassette not loaded or
unloaded
No tape running, tape
slack
Tape slack
Video head cleaning procedure
1. Apply one drop of cleaning liquid to the cleaning paper with the baby oiler.
2. Gentlypressthecleaningpaperagainstthevideoheadtofixyourfinger,andmovetheupperdrumsothateachhead
is passed to and fro 5 times (do not move the cleaning paper).
3. Wipe with the dry cleaning paper.
Notes :
• Use the commercially available ethanol of Class 1 as
cleaning liquid.
• Since the video head may be damaged, do not move up
and down the cleaning paper.
• Whenever the video head is cleaned, replace the clean-
ing paper.
• Do not apply this procedure for the parts other than the
video head.
Parts Code Description Code
ZPAPRA56-001E Cleaning Paper AW
ZOiLR-02-24TE Babe Oiler (Spoit) AH
Gently press the cleaning paper to
fix with your finger, and rotate the
upper drum to clean.
Move to and fro 5 times for each head.
(Do not move the cleaning paper.)
Rotate the upper drum
with one hand.

10
VC-MH75HM
Figure 4-1.
• Reassembly
1. Before installing the cassette housing control, short-
circuit between TP803 and TP802 provided at main
PWB, press the eject button. The master cam turns and
stop in eject position. Fit the drive lever to master cam
through main chassis, push down and slide the drive
lever towards to master cam.
*Ejectposition:Pinch DriveCampositioningholeparal-
lel to center of Synchro Gear (Synchro gear marking
line). Synchro Gear positioning mark parallel to center
of master cam.
Figure 4-2.
2. Install in the reverse order of removal.
Notes
1. Inthecasewhenyouusethemagnetscrewdriver,never
approach the magnet driver to the A/C head, FE head,
and drum.
2. When installing or removing, take care so that the
cassette housing control and tool do not contact the
guide pin or drum.
3. After installing the cassette housing control once per-
form cassette loading operation.
4-4 TORUNATAPEWITHOUTTHECASSETTE
HOUSING CONTROL ASSEMBLY
1. Remove the full-surface panel.
2. Short-circuit between TP803 and TP802.
3. Plug in the power cord.
4. Turn off the power switch.
(The pole bases move into U.L.position.)
5. Open the lid of a cassette tape by hand.
6. Hold the lid with two pieces of vinyl tape.
7. Set the cassette tape in the mechanism chassis.
8. Stabilize the cassette tape with a weight (500g) to
prevent floating.
4-3 REMOVING AND INSTALLING THE CAS-
SETTE HOUSING
• Removal
1. In the cassette removing mode, remove the cassette.
2. Unplug the power cord.
3. Remove in the following numerical order.
a) Remove two screws 1.
b) Pullandcircle the drivelever andpull upthecassette
housing control.
Figure 4-3.
9. Turn on the power switch.
10. Perform running test.
Note:
The weight should not be more than 500g.
To take out the cassette tape.
1. Turn off the power switch.
2. Take out the cassette tape.
1
500g
Weight to prevent
float (500g)
Mechanism chassis
From Bottom View
Pinch Drive
Cam
Synchro
Gear
Master
cam
From top view
Main chassis
Drive
Lever
Phase
matching
Master cam
Line of
synchro
gear.
Hole of Pinch
drive cam.

11
VC-MH75HM
4-5 REEL DISK REPLACEMENT AND HEIGHT
CHECK
• Removal
1. Remove the cassette housing control assembly.
2. Remove the Supply/Take-up main brake ass'y.
3. Remove tension band from the tension arm ass'y.
4. Remove the reel disk.
Note:
Take care so that the tension band ass'y and main brake
ass'y are not deformed.
Notes:
1. When installing the reel disk, take due care so that the
tension band ass'y is not deformed and grease does no
adhere.
2. Donot damage the Supplymain brake ass'y. Be careful
so that grease does not adhere to the brake surface.
• Reassembly (Take-up reel disk)
1. Clean the reel disk shaft and apply grease (SC-141) to
it.
2. Align the phase of the reel disk to that of the reel relay
gearandtoinstallanewtake-upreeldiskontotheshaft.
3. Check the reel disk height and reassemble the take-up
main brake ass'y.
Note:
1. Take care so that the Take-up main brake ass'y is not
damaged.Takecaresothatgreasedoesnotadherethe
brake surface.
2. After reassembly, check the video search rewind back
tension (see 4-10), and check the brake torque (see 4-
14).
• Height checking and adjustment
Note:
1. Set the master plane with due care so that it does not
contact the drum.
2. When putting the master plane, shift the reverse guide
alittleintheloadingdirection.Care must be taken since
excessive shift results in damage.
Figure 4-4.
Note:
• Check that the reel disk is lower than part A but higher
than part B. If the height is not correct, readjust the reel
diskheightbychangingthepoly-sliderwasherunderthe
reel disk.
• Reassembly (Supply reel disk)
1. Clean the reel disk shaft and apply grease (SC-141) to
it.
2. Matchthephasesofreeldiskandreelrelaygear,andset
the new reel disk.
3. After checking the reel disk height, wind the tension
bandass'yaroundthereeldisk,andhooktotensionarm
ass'y.
4. Assemble the Supply main brake ass'y.
Take-up reel diskSupply reel disk
Ten
Tension arm ass'ySupply main brake
Tension band
ass'y
Take-up main brake ass'y
Supply reel disk
Take-up reel disk
Cassette lock
release shaft
Master plane

12
VC-MH75HM
Note:
Wheneverreplacingthereeldisk,performtheheightcheck-
ing and adjustment.
Notes:
1. Hold the torque gauge by hand so that it is not moved.
2. Donotkeepthereeldiskinlockstate.Donotallowlong-
time measurement.
4-7 CHECKINGANDADJUSTMENTOFTAKE-
UP TORQUE IN REWIND MODE
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Setting
1. Set a torque gauge to zero on the scale. Place it on the
supply reel disk.
2. Press the rewind button.
3. To calculate the remaining capacity, slowly rotate the
take-up reel disk, and then shift it into the rewind mode.
• Checking
1. Turn the torque gauge slowly (one rotation every 2 to 3
seconds) by hand in the CCW direction.
2. Makesurethattheindicationoftorquegaugeisnotless
than 30mN·m (306gf·cm).
AB
Figure 4-5.
Master plane Reel disk height
adjusting jig
Mechanism chassis
Reel disk
10 ± 0.2mm Reel disk
4-6 CHECKINGANDADJUSTMENTOFTAKE-
UP TORQUE IN FAST FORWARD MODE
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Setting
1. Set a torque gauge to zero on the scale. Place it on the
take-up reel disk.
2. Press the FF button.
3. To calculate the remaining capacity of the play back
mode, slowly rotate the supply reel disk, and then shift
it into the forward mode.
• Checking
1. Turn the torque gauge slowly (one rotation every 2 to 3
seconds) by hand in the CW direction.
2. Makesurethattheindicationoftorquegaugeisnotless
than 30mN·m (306gf·cm).
Figure 4-7.
Torque gauge
Supply reel disk
Idler ass'y
30The gauge is held at
its maximum value.
(Red mark)
• Adjustment
1. Iftherewindwinding-uptorqueislessthanthespecified
value, clean the capstan D.D. pulley, reel belt, and
limiter pulley with cleaning liquid, rewind again, and
check the winding-up torque.
2. If the winding-up torque is still out of range, replace the
drive belt.
Figure 4-6.
Torque gauge
30mN·m (306gf·cm)
or more
The gauge is held at
its maximum value.
(Red mark)
Idler ass'y
• Adjustment
1. If the FF winding-up torque is less than the specified
value, clean the capstan D.D. pulley, reel belt, and
limiter pulley with cleaning liquid, and check again.
2. If the torque is less than the set value, replace the reel
belt.
CCW
CW
30mN·m (306gf·cm)
or more

13
VC-MH75HM
Notes:
1. Hold the torque gauge by hand so that it is not moved.
2. Donotkeepthereeldiskinlockstate.Donotallowlong-
time measurement.
4-8 CHECKINGANDADJUSTMENTOFTAKE-
UP TORQUE IN RECORD/PLAYBACK
MODE
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Turn off the power switch.
• Open the cassette torque meter lid, and fix it with
tape.
• Load the cassette torque meter into the unit.
• Put the weight (500g) on the cassette torque meter.
• Turn on the power switch.
• Press the picture record button, and set LP picture
record mode (x2).
4-9 CHECKINGANDADJUSTMENTOFTAKE-
UP TORQUE IN VIDEO SEARCH REWIND
MODE
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Setting
Press the playback button and rewind button to set the
video search rewinding mode.
• Checking
Place the torque gauge on the supply reel disk, and turn it
counterclockwise very slowly (one rotation every 1 to 2
seconds) and check that the torque is within the set value
14.1 ± 3.5mN⋅m. (144 ± 35gf⋅cm)
Set value LP 6.9 mN⋅m (70 gf⋅cm)
Figure 4-8.
• Checking
1. Make sure that value is within the setting 6.9 mN·m
(70 gf·cm).
2. The winding-up torque fluctuates due to variation of
rotation torque of limiter pulley ass'y. Read the center
value of fluctuation as setting.
3. Set the LP record mode (x2) and make sure that the
winding-up torque is within setting.
• Adjustment
If the playback winding-up torque is not within the setting,
replace the limiter pulley assembly.
Note:
When the torque cassette is set, put a weight (500g) to
prevent rise.
When the cassette torque meter is taken out.
Turn off the power switch.
Figure 4-9.
Note:
Surely put the torque gauge on the reel disk to measure. If
the torque gauge is raised, accurate measurement is
impossible.
• Adjustment
Iftherewindingplaybackwinding-uptorqueisnotwithinthe
setting, replace the limiter pulley assembly.
Note:
The winding-up torque fluctuates due to variation of rota-
tion torque of supply reel disk. Read the center value of
fluctuation as setting.
Torque gauge
Supply reel disk
CCW
+20
–25
+2.0
–2.5
+2.0
–2.5 +20 –25
500g
Cassette torque meter

14
VC-MH75HM
Figure 4-11.
4-12 CHECKING AND ADJUSTMENT OF
TENSION POLE POSITION
4-10 CHECKINGTHEVIDEOSEARCHREWIND
BACK TENSION
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Checking
1. After pressing the play button, press the rewind button,
and set the video search rewind mode.
2. Placethetorquegaugeonthetake-upreeldisk,andturn
it counterclockwise very slowly (one rotation every 2 to
3 seconds) and check that the torque is within the set
value 3.7 ± 1.5mN⋅m (38 ± 15gf⋅cm).
Pinch roller Tension gauge
900 - 1,200gf
Capstan shaft
Tension gauge adapter
Figure 4-10.
Torque gauge
Take-up reel disk
Notes:
Set the torque gauge securely on the take-up reel disk.
If it is not secure, the measurement will be incorrect.
4-11 CHECKING THE PINCH ROLLER
PRESSURE
CCW
Figure 4-12.
500g
Weight to prevent
float (500g)
(E-180)
• Remove the cassette housing control assembly.
• Aftershort-circuitingbetweenTP803andTP802pro-
vided at main PWB, plug in the power cord.
• Checking
Press the play button to set the playback mode.
1. Detach the pinch roller from the capstan shaft.
Do not separate excessively. Or the pinch lever and
pinch double action lever may disengage.
2. Engage the tension gauge adapter with the pinch roller
shaft, and pull in the arrow direction.
3. Gradually return the pinch roller, and measure the pull-
ing force when the pinch roller contacts the capstan
shaft.
4. Make sure that the measured value is within setting
change to 9.8 ± 2N (1.0 ± 0.2kgf).
∗Checking can be perform with or without
cassette housing control.
• Remove the cassette housing control assembly.
• Aftershort-circuitingbetweenTP803andTP802pro-
vided at main PWB, plug in the power cord.
• Setting (without cassette housing control)
1. Turn off the power switch.
2. Open the cassette tape (E-180), and fix with tape.
3. Set the cassette tape in loading state.
4. Put the weight (500g) on the cassette tape.
5. Turn on the power switch.
6. MaketheadjustmentwiththebeginningofaE-180tape.
∗Checking can be perform with or without
cassette housing control.
• Setting (with cassette housing control)
1. Insert cassette tape (E-180).
2. Maketheadjustment with the beginning of aE-180
tape.

15
VC-MH75HM
• Checking
1. Set a cassette tape, push the REC button to place the
unit in the SP record mode. Now check the tension pole
position.
2. Visuallychecktoseeifthe positionofthetensionpoleis
within the 0 mm from the left side line.
Insert the tension pole adjustment driver to main chassis
hole, and rotate counterclockwise.
Figure 4-15.
At left side from the reference line. (A).
Figure 4-13.
Figure 4-14.
Insert the tension pole adjustment driver to main chassis
hole, and rotate clockwise.
At right side from the reference line. (A).
Tension pole adjustment driver adjusting direction
4-13 CHECKING AND ADJUSTMENT OF
RECORD/PLAYBACK BACK TENSION
Make the adjustment with the beginning of a E-180 tape.
Figure 4-16.
Figure 4-17.
A
A
A
Tensionpole
adjustment
driver
CW
CCW
Cassette torque
meter
500g
Weight to prevent
float (500g)
Standard A = 0 mm
+ 0.5
- 0.2
• Checking
1. Push the REC button to place the unit in the SP record
mode.
2. At this time ascertain that the back tension is within the
setting 3.9 to 5.5mN⋅m (40 to 56gf·cm) by seeing the
indication of torque cassette meter.
+ 0.5
– 0.2
• Setting (with cassette housing control)
1. Insert cassette torque meter.
∗Checking can be perform with or without
cassette housing control.
• Remove the cassette housing control assembly.
• Aftershort-circuitingbetweenTP803andTP802pro-
vided at main PWB, plug in the power cord.
• Setting (without cassette housing control)
1. Turn off the power switch.
2. Open the cassette torque meter and fix with tape.
3. Set the cassette torque meter in loading state.
4. Put the weight (500g) on the cassette torque meter.
5. Turn on the power switch.

16
VC-MH75HM
• Adjustment
1. If the indication of torque cassette meter is lower than
the setting, shift the tension spring engagement to the
part A.
2. If the indication of torque cassette meter is higher than
the setting, shift the tension spring engagement to the
part B.
• Checking the brake torque at the take-up side
Figure 4-20.
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Setting
1. Switch from the FF mode to the STOP mode.
2. Disconnect the power cord.
3. Set a torque gauge to zero on the scale. Place it on the
take-up reel disk.
4. Please check Idler gear not contact with reel relay gear
(TU side)
• Checking
1. Turn the torque gauge at a rate of about one turn/2 sec
in the CCW direction/CW direction so that the reel disk
and torque gauge pointer rotates at equal speed and
make sure that the value is within the setting (CCW
direction: 4.41 ± 1mN·m (45 ± gf·cm), CW direction:
4.12 ± 1.mN·m (42 to gf·cm).
2. Adjustmentofthebraketorqueatthesupplysideandthe
take-up side
• Unless the supply side brake torque or take-up side
brake torque is within the setting, clean the felt surface
of reel disk (supply, take-up) brake lever, check again
the brake torque.
• If value cannot be set within the setting yet, replace the
main brake ass'y or main brake spring.
Figure 4-18.
4-14 CHECKING THE BRAKE TORQUE
• Checking the brake torque at the supply side
Figure 4-19.
• Remove the cassette housing control assembly.
• After short-circuiting between TP803 and TP802
provided at main PWB, plug in the power cord.
• Setting
1. Set a torque gauge to zero on the scale. Place it on the
supply reel disk.
2. Switch from the FF mode to the STOP mode.
3. Disconnect the power cord.
4. Please check Idler gear not contact with reel relay gear
(SU side)
Tension arm
Tension spring
CW
CCW CW
Supply reel disk
Torque gauge
Torque gauge
CCW
Take-up reel
disk
AB
CCW: 4.41 ±mN⋅m (45 ±gf⋅cm)
CW: 4.12 ±mN⋅m (42 ±gf⋅cm)
• Checking
Turn the torque gauge at a rate of about one turn/2 sec
in the CW direction/CCW direction with respect to the
supply reel disk so that the reel disk and torque gauge
pointer rotate at equal speed, and make sure that the
valueiswithinthe setting (CW direction: 4.12 ± mN·m
(42 gf·cm);CCWdirection:4.41 mN·m(45 15gf·cm).
+15
–12 +2.0
–1.5 +20 –15
+1.5
–1.2
CCW: 4.41 ±mN⋅m (45 ±gf⋅cm)
CW: 4.12 ±mN⋅m (42 ±gf⋅cm)
+2.0
–1.5
+1.5
–1.2
+20
–15
+15
–12
+2.0
–1.5 +20
–15
+1.5
–1.2 +15 –12
+2.0
–1.5
+1.5
–1.2
+20
–15
+15
–12

17
VC-MH75HM
Figure 4-22.
• Replacement
1. Solder the removed PWB to the new head assembly.
2. Adjusttheheightfrom the A/C headarm(lowersurface)
to the A/C head plate to 10.8mm with slide calipers. (3
placesofazimuthscrewsection,tiltscrewsectionandA/
C head front section) (See the figure below.)
3. Align the left end of gear of A/C head arm with the
punched mark of chassis, tentatively tighten the screws
1so as to ensure smooth motion of A/C head arm.
Tightening torque must be 0.45 ± 0.05N·m (4.5 ±
0.5kgf·cm).
4-15 REPLACEMENTOFA/C(AUDIO/CONTROL)
HEAD
1. In eject position unplug the power cord.
• Removal
1. Take out FFC holder from main chassis.
(Push 3 hooking point and pull-up the
holder).
2. Remove the screws 123, Tilt screw.
3. Unsolder the PWB fitted to the A/C head.
Notes:
1. When replacing, never touch the head. If you touched,
clean with the cleaning liquid.
2. When removing the screw 3, take care so that the
spring may out.
Figure 4-23.
Note:
1. If the screw 1is tighten tentatively too loose, the
azimuth and height of A/C head may change when they
are finally tightened. Therefore care must be taken.
2. After completion of A/C head be sure to adjust tape
running.(Executetherunningadjustmentbythemethod
described in 4-17.)
Figure 4-21.
Height screw
Left end of A/C head arm gear
Punched line mark on chassis
1
3
1
2
A/C head screw
Azimuth spring
Height adj. screw
A/C head PWB ass'y
(with A/E)
Tilt screw
Height Adj. spring
A/C head PWB
Azimuth adj. screw
*Derection designation.
(The bottom part is big.)
A/C head plate
10.8mm
A/C head FFC
A/C FFC holder
Solder
A/C head PWB
New A/C head ass'y
A/C head plate
*Fit the groove of FFC to
the boss of the holder.
AC Head
FFC
Holder

18
VC-MH75HM
4-17 ADJUSTMENT OF TAPE DRIVE TRAIN
1. Tape run rough adjustment
1Check and adjust the position of the tension pole.
(See 4-12.)
2Check and adjust the video search rewind back
tension. (See 4-10.)
3ConnecttheoscilloscopetothetestpointforPBATR
signal output (TP201). Set the synchronism of the
oscilloscope to EXT. The PB ATR signal is to be
triggered by the head switching pulse (TP202).
4Set the alignment tape (VROCPSV) to play.
Figure 4-26.
5Press the tracking button (+), (–) and change the
ATR signal waveform from max to min and from min
to max. At this time make sure that the ATR signal
waveform changes nearly parallel.
6Unless the ATR signal waveform changes nearly
parallel,adjusttheheightofsupplysideandtake-up
side guide roller so that the envelope waveform
changesnearlyparallel.(ForATRsignaladjustment
procedure refer to Figure 4-30.)
7Turn the tilt screw to remove the tape crease at the
fixing guide flange.
Playback the tape and check for tape crease at the
fixing guide flange.
(1)If there is no tape crease
Turn the tilt screw clockwise so that tape crease
appearsonceattheflange,andthenreturnthetilt
screw so that the crease disappears.
(2)If there is tape crease
Turn counterclockwise the tilt screw so that the
tape crease disappears.
(Reference) If the tilt screw is turned clockwise
crease appears at the lower flange.
Guide roller
Cassette Tape
Figure 4-24.
Figure 4-25.
Tape
0.3mm
A/C head
• Adjustment
Adjust the height screw visually so that the control head is
visible 0.3mm below the bottom of the tape.
1. Set the cassette tape in the unit.
2. Press the PLAY button to put the unit in the playback
mode.
3. Roughlyadjustthe height oftheA/Cheadby turning the
height screw until the tape is in the position shown
below.
4-16 A/CHEADHEIGHTROUGHADJUSTMENT
• Setting
Mechanism chassis
Cassette tape
Height screw
TiH screw
Azimuth screw
500g
Weight to prevent
float (500g)

19
VC-MH75HM
Notes:
1. Previouslysetthetrackingcontrolinthecenterposition,
andadjustthe ATR signalwaveformtomaximumwith X
value adjustment nut. Thereby the tape run rough ad-
justment is facilitated.
2. Especially the outlet side ATR signal waveform must
have higher flatness.
2. Adjustment of A/C head height and azimuth
1PerformtheinitialsettingofA/Cheadpositionbythe
method stated in "4-15 Replacement 3".
2Connect the oscilloscope to the audio output termi-
nal.
3Usingthealignment tapeinwhich1 kHzlinearaudio
signalhasbeenrecorded,adjusttheheightscrewso
as to get max audio output.
4Usingthealignment tapeinwhich7 kHzlinearaudio
signal has been recorded, adjust the azimuth screw
so as to get max audio output.
5The adjustment of 3and 4twice or three times
repeat, and finally adjust 4.
Figure 4-27.
For X value adjustment
Adjust the X value, turning the gear-
type screwdriver.
Figure 4-28.
3. Tape run adjustment
1Connect the oscilloscope to PB ATR signal output
testpoint,setoscilloscopesynctoEXT,trigger-input
the PB CHROMA signal (head switching pulse).
2Rough adjustment of X value
TentativelyfixA/Cheadarmscrews1bythemethod
described in 4-15 "Replacement 3".
Playback the alignment tape (VROCPSV) and
shortcircuit between TP801 and TP802. As a result
the auto-tracking is automatically cancelled, so that
the X value adjustment mode is set.
MovetheA/CheadwiththeXvalueadjustmentgear
driver (JiGDRiVER-6) by the method shown in Fig-
ure 4-33, and adjust the A/C head so as to get the
maximumATRsignalwaveform.(Note:WhentheA/
Cheadisadjusted,adjustsothatthemaximumATR
signal waveform is obtained nearest the position of
initial setting made in 4-15.)

20
VC-MH75HM
3Next, press the tracking button (+), (–) and change
the ATR signal waveform from max to min and from
min to max. At this time adjust the height of supply
and take-up side guide roller with the adjustment
driver(JiGDRiVERH-4)sothattheATRsignalwave-
form changes nearly parallel.
4If the tape is lifted or sunk from the helical lead
surface, the PB ATR signal waveform appears as
shown in Figure 4-30.
5Pressthetrackingbutton (+), (–)andmakesurethat
the ATR signal waveform changes nearly parallel.
6Finally, check tape crease near the reverse guide. If
tape crease is found, adjust tilt screw 45˚ counter
clockwise. Small tape crcase will appear at retain
guide after this adjustment finished.
3MovetheA/CheadwiththeXvalueadjustmentgear
driver by the method shown in Figure 4-33, and
adjust the A/C head so as to get the maximum ATR
signal waveform. (Note: At this time adjust so as to
get the maximum ATR signal waveform nearest the
A/C head position which has been set in case of X
value rough adjustment as stated in 4-17, 3- 2.)
4Adjust the playback switching point (Refer to the
electric adjustment method.)
5Playback the self-picture-recorded tape, and check
the flatness of ATR signal waveform and sound.
Notes:
When the A/C head X value adjustment is performed, be
suretoperformatfirstXvalueroughadjustment(referto4-
17, 3-2).
PB ATR
Signal
Head switching pulse
Figure 4-29.
4. A/C head X value adjustment
1FixA/Cheadarm screws1by the method described
in 4-15 "Replacement 3".
2Playback the alignment tape (VROCPSV), and
shortcircuit between TP801 and TP802. As a result
the auto-tracking is automatically cancelled, so that
the X value adjustment mode is set.
Take-up side Supply side Take-up side
Adjustment
Supply side
Supply side guide roller
rotated in clockwise
direction (lowers guide
roller) to flatten
ATR signal.
Take-up side guide roller
rotated in clockwise
direction (lowers guide
roller) to flatten
ATR signal.
Supply side guide roller
rotated in counterclock-
wise direction (raises
guide roller) to make the
tapefloatabove the helical
lead. The supply
side guide roller is then
rotated in the clockwise
direction to flatten the
ATR signal.
Take-up side guide roller
rotated in counterclock-
wise direction (raises
guide roller) to make the
tape float above the
helical lead. The take-up
side guide roller is then
rotated in the clockwise
direction to flatten the
ATR signal.
Figure 4-30.
When the tape is below the helical lead.When the tape is above the helical lead.
Figure 4-31.
1

21
VC-MH75HM
4-19 REPLACEMENT OF DRUM D.D. MOTOR
1. Set the ejection mode.
2. Withdraw the main power plug from the socket.
• Removal (Perform in numerical order.)
1. Disconnect the FFC cable 1.
2. Unscrew the D.D. stator assembly fixing screws 2.
3. Take out the D.D. stator assembly 3.
4. Unscrew the D.D. rotor assembly fixing screws 4.
5. Take out the D.D. rotor assembly 5.
Notes:
1. In removing the D.D. stator assembly, part of the drum
earth spring pops out of the pre-load collar.
Be careful not to lose it.
2. Install,sothat the D.D.rotorass'yandupper drum ass'y
mounting direction check holes align.
(Align the upper drum dent with the rotor hole.)
3. Be careful not to damage the upper drum or the video
head.
4. Protecttheholeelementsfromshockduetocontactwith
D.D. stator or D.D. rotor ass'y.
5. After installation adjust the playback switching point for
adjustment of servo circuit.
4-18 REPLACEMENT OF THE CAPSTAN D.D.
(DIRECT DRIVE) MOTOR
• Remove the mechanism from the set.
• Removal (Follow the order of indicated numbers.)
1. Unsolder loading motor wire and drum FFC .
2. Remove the reel belt 1.
3. Remove the three screws 2.
• Reassembly
1. Taking care so that the capstan shaft does not contact
the mechanism chassis, set its position on the mecha-
nism chassis, and then install with the three screws.
2. Install the reel belt.
3. Solder loading motor wire and insert drum FFC .
Notes:
1. AfterinstallingthecapstanD.D.motor,be sure to rotate
the capstan D.D. motor and check the movement.
2. Set the tape, and check for the tape crease near the
reverse guide in the playback mode. Adjust the A/C
head and azimuth as stated in 4-17 item 2.
Figure 4-33.
Figure 4-32.
2
21
4
5
4
D.D. rotor ass'y
D.D.stator ass'y
Upper drum
FFC
Capstan
D.D. motor
Main chassis
1 Reel belt
2
Solder drum FFC
Solder loading motor wire

22
VC-MH75HM
4-21 ASSEMBLING OF PHASE MATCHING
MECHANISM COMPONENTS
• Assemble the phase matching mechanism compo-
nents in the following order.
1. Assemble the reverse guide lever and pinch drive cam.
2. Mounting the shifter (on the back of the mechanism
chassis).
3. Mounting the master cam (on the back of the mecha-
nism chassis).
4. Assemble synchro gear.
5. Assemble the loading motor parts.
• PINCH DRIVE CAM AND REVERSE GUIDE
LEVER ASSEMBLING METHOD.
(Placethefollowingpartsinpositioninnumericalorder.)
(1)Pinch drive cam 1
(2)Reverse guide spring 2
(3)Reverse guide lever ass’y 3
(4)Open guide 4
4-20 REPLACING THE UPPER AND LOWER
DRUM ASSEMBLY
• Replacement (Perform in the numerical order)
1Removethemotorasstatedin4-19D.D.motorreplace-
ment.
2Remove the drum earth brush ass’y 2.
3Removetheupperandlowerdrumassemblyfrommain
chassis 1.
4Remove the drum FFC holder 3.
[Cares when replacing the drum]
1. Be careful so that the drum earth brush is not lost.
2. Do not touch directly the drum surface.
3. Fit gently the screwdriver to the screws.
4. Since the drum assembly is an extremely precise as-
sembly, it must be handled with utmost care.
5. Make sure that the drum surface is free from dust, dirt
and foreign substances.
6. After replacing the drum be sure to perform the tape
running adjustment.
After that, perform also the electrical adjustment.
• Playback switching point adjustment
• X-position adjustment and check
• Standard and x-3 slow tracking adjustment
7. After replacing the drum clean the drum.
Figure 4-34.
Figure 4-35.
2
1
3
Lower drum bottom side
4
2
3
1
Dot B
Dot A
Insert it into the
groove of the shaft
Don't run up
on the spring
1
3
2Synchro gear
From Top View

23
VC-MH75HM
Figure 4-37.
4-22 INSTALLING THE SHIFTER
Figure 4-36.
1. MakesurethattheloadingarmTandSareatthePhase-
Matching point as shown below .
2. Fix the shifter position setting part to the roading arm T
position setting part as shown in figure .
3. Make sure tension arm not run on the shifter as shown
in figure .
a
b
c
Loading arm (T)
Shifter
Insert point
Loading arm (T) Loading arm (S)
Phase matting
*Not run on the
sifter.
Sifter
Tension arm
a
c
b
Drum
Capstan D.D.
motor
(Bottom side of mechanism chassis)