VC-MH85 (serv.man4). Trouble shooting guide — Sharp VCR Service Manual (repair manual)

Model
VC-MH85 (serv.man4)
Pages
15
Size
76.47 KB
Type
PDF
Document
Service Manual
Brand
Device
VCR / Trouble shooting guide
File
vc-mh85-sm4.pdf
Date

View Sharp VC-MH85 (serv.man4) Service Manual online

41
VC-MH705HM/LM
VC-MH815HM/LM,MH85HM
VC-MH715HM,MH835HM
7. ELECTRICAL TROUBLESHOOTING
FLOW CHART NO.1 POWER TROUBLESHOOTING(1)
No power.
The fuse blows out even when it is 
replaced with new one.
See FLOW CHART NO.2  
POWER TROUBLESHOOTING (2)
<In case of Fuse (F901) blown out.>
YES
YES
YES
NO
NO
NO
NO
Is the fuse good?
Is the normal state restored when 
once unplugged power cord is 
plugged again after several seconds?
Check for leak or short-circuiting 
of primary circuit part
(D901~906, Q901~903, T901, 
C906, L901, D912 etc.), replace 
defective parts.
Are AT 5V voltage line normal?
Are AT 5V and AT 12V lines normally?
Check each rectifier circuits and 
short-circuit of secondary circuit.
FLOW CHART NO.2 POWER TROUBLESHOOTING(2)
In case of Fuse (F901) blown out.
Check for leak or short-circuiting of 
primary circuit part (D901~906, Q901
~903, T901, C906, L901, D912 etc.), 
replace defective parts.
Check for short-circuit of rectifying 
diode and circuit in each rectifying 
circuit of secondary circuit.(D934, 
D933, D932, D931)
FLOW CHART NO.3 POWER TROUBLESHOOTING(3)
In case of abnormal noise (sound).
Check for short circuit of rectifying diode of each rectifying circuit of secondary circuit 
and check for shunt regulator circuit. (D934, D933, IC903, C9335~9336)
FLOW CHART NO.4 POWER TROUBLESHOOTING(4)
In case of output voltage at low level.
Check whether the secondary side 
photocoupler circuit operates normally.
(IC903,C9336,R930,R932,R933)
Check the circuit and replace 
defective parts. (IC901, IC903, etc.)
NO
YES
Check whether the primary side 
photocoupler output control function 
normally. (Q901 & Q902)
Check the circuit and replace 
defective parts. (IC901, IC903, Q902, 
T901, etc.)
NO
YES
Replace IC901.
YES
YES
YES
NO
NO
NO
FLOW CHART NO.5 SYSTEM CONTROL TROUBLESHOOTING
No power is turned on.
Does power control (H) signal at pin(96) 
of IC701 change from "L" to "H" level?
Check IC701.
Does the base voltage of Q966 
change from about 12.6V to 11.8V?
Check line between Q966, Q967 and 
IC701.
Is voltage of 12V sent out from the 
collector of Q966 transistor?
Check peripheral circuit of or Q966 
and AT 12V line.
YES
YES
YES
NO
NO
Does the base voltage of Q961 
change from about 5.5V to 6.2V?
Check line between emitter of or Q966 
and base of Q961.
Is voltage of 5V sent out from the 
emitter of Q961 transistor?
Check peripheral circuit of Q961 and 
AT 5V line.
Check peripheral circuit for poor 
soldering.
42
VC-MH705HM/LM
VC-MH815HM/LM,MH85HM
VC-MH715HM,MH835HM
FLOW CHART NO.7 KEY CONTROL TROUBLESHOOTING(2)
Does the key switch make good 
contact, when the cassette tape is 
inserted?
Check switch contact.
Is there the function control voltage 
inputted at the pins(88) and (89) of 
IC701, when the keys are activated?
Replace IC701.
Check peripheral circuit of pins(88) 
and (89) of IC701, and the function 
keys.
YES
NO
NO
YES
Key-in input is not received 
<Except for jog shuttle mode
.>
FLOW CHART NO.8 INFRARED R/C TROUBLESHOOTING
No operation is possible from the infrared remote control.
Does the infrared remote control 
function?
Replace infrared remote control as 
required.
Is the supply voltage of 5V fed to pin(2) 
of RMC801?
Check AT 5V and GND lines.
Is "L" pulse sent out from pin(1) of the 
receiver when the infrared remote control 
is activated?
Replace receiver.
Check between at pin(1) of receiver and 
all the way up through to pin (4) of IC701.
Replace IC701.
YES
NO
YES
NO
NO
NO
YES
Is the cassette housing distorted?
Fix or replace the cassette housing.
NO
YES
YES
YES
YES
NO
YES
NO
NO
YES
NO
YES
FLOW CHART NO.9 CASSETTE CONTROL TROUBLESHOOTING(1)
A cassette tape is not take in.
NO
NO
Check start sensor cover.
Check line between start sensor and 
pin (87) of IC701
Check line between pin (92) of IC701 
and pin(10) of P701.
Is the supply voltage of 12V fed to pin 
(8) of P701?
Check M 12V  lines.
Check IC on mechanism.
Check line between  IC on mechanis 
and loading motor.
Replace loading motor.
Is the specified voltage applied at the 
loading motor terminal when the cassette 
tape is inserted?
Does  IC on mechanism output to about 
10V when the cassette tape in inserted?
Does pin(87) of IC701 change from"H" 
to "L" level when the cassette tape is 
inserted?
Does the start sensor cover go to open 
when the cassette tape is inserted?
SWITC
FUNCTION
SWITC
FUNCTION
TERMINAL
Ref No.                                 Ref No.
                          VOLTAGE
S805
SET
S801
POWER
0.000V
S806
CH(+)
S802
EJECT
0.652V
S807
TAPE SPEED / PAUSE
S803
MENU
1.250V / 1.864V
S808
PAUSE / REC
S804
CH(-)
1.864V / 2.561V
S883
REC / NO USE
S881
PLAY
S884/S885
REW
S882
STOP
3.081V
S886/S887
FF
TP801
TEST
3.694V
-
-
TP802
CASSETTE
4.279V
-
-
-
-
5.000V
KEY-1 IN
KEY-0 IN
(Pin88 of IC701)
(Pin89 of IC701)
Does pin(10) of P701 go to a "H" level 
when the cassette tape is inserted?
YES
YES
YES
NO
NO
NO
FLOW CHART NO.6 POWER TROUBLESHOOTING(6)
In case of output voltage at low level.
Check peripheral circuits IC901, IC903, 
C9336, R932, R930 and R933.
The result of IC901, IC903, C9336, R932,R930 and 
R933. Replace where necessary. 
Check C901 and peripheral circuits of 
IC901.
Replace IC901.
Check short-circuit or leak of T901.
Replace T901.
Check primary circuit and peripheral 
circuit of Q901 and Q902.
43
VC-MH705HM/LM
VC-MH815HM/LM,MH85HM
VC-MH715HM,MH835HM
NO
NO
NO
FLOW CHART NO.10 CASSETTE CONTROL TROUBLESHOOTING(2)
A cassette tape is taken in, but ejected at once.
Does the start sensor pulse at pin (87) 
of IC701 change from "L" to "H" level 
when the cassette tape is loaded?
Check line between start sensor and pin 
(87) of IC701.
Does the end sensor pulse at pin (86) 
of IC701 change from "L" to "H" level 
when the cassette tape is loaded?
Check line between end sensor and pin 
(86) of IC701.
Does the master cam mode shifter 
operate normally when the cassette 
tape is loaded?
Check line between cam switch and 
IC701.
Replace IC701.
YES
YES
YES
FLOW CHART NO.11 LOADING MOTOR AND EJECT TROUBLESHOOTING
The cassette tape fails to come out.
Does the capstan motor start when the 
EJECT button is pressed?
See FLOW CHART NO.12. CAPSTAN 
MOTOR TROUBLESHOOTING
Does the take-up reel disk turn when the 
capstan motor is running?
Check line between take-up reel 
sensor and pin(2) of IC701.
Is a "H" level applied at pin(10) of P701 
when a reel pulse has been inputted?
Check line between pin(92) of IC701 
and pin(10) of P701.
Is the supply voltage of 12V fed to 
pin(8) of P701?
Is the voltage about 10V sent out from 
IC on mechanism?
Check IC on mechanism.
Is the specified voltage applied at the 
loading motor terminal?
Check line between IC on mechanism 
and loading motor.
Does the loading motor run?
Replace loading motor.
Replace cassette cam, gear, etc.
YES
YES
YES
Check M 12V lines.
NO
YES
NO
YES
YES
YES
NO
NO
NO
NO
NO
FLOW CHART NO.12 CAPSTAN MOTOR TROUBLESHOOTING
The capstan motor fails to run.
Is the voltage more than about 2.6V 
DC given out of pin(29) of IC701?
Check IC701.
NO
NO
NO
NO
NO
YES
YES
YES
YES
Is the supply voltage of 5V fed to 
pin(3) of P701?
Check PC 5V line.
Is the voltage more than 2.6V DC 
sent in pin(9) of P701?
Check line between pin(9)  of P701
 and pin(29) of IC701.
Is the voltage of pin(5) of P701 is 
1.6~2.7V? 
Check line between the pin(91) of 
IC701 and pin(5) of P701.
Is the supply voltage of 12V/20V fed 
to pin(2) of P701? 
YES
Replace capstan motor.
Check MOTOR Vcc line and motor 
voltage selector circuit.
44
VC-MH705HM/LM
VC-MH815HM/LM,MH85HM
VC-MH715HM,MH835HM
FLOW CHART NO.14 DRUM MOTOR TROUBLESHOOTING(1)
The drum motor fails to run.
Is the voltage more than about 2.6V 
DC given out of pin(30) of IC701?
Check IC701.
NO
NO
YES
Is the voltage more than about 2.6V 
DC given out of pin(12) of P701?
Check line between pin(30) of IC701 
and pin(12) of P701.
NO
YES
YES
Is the supply voltage of 12V fed to 
pin(8) of P701?
Replace drum motor.
Check M 12V line.
FLOW CHART NO.15 DRUM MOTOR TROUBLESHOOTING(2)
The drum motor runs only for a few seconds.
Replace IC on mechanism.
Check peripheral circuit of IC on 
mechanism
Is drum PG signal given out from the 
pin (11) of P701?
Is drum PG signal fed to pin(65) of 
IC701?
Check line between pin(11) of P701 
and pin(65) of IC701.
Is head switching pulse sent out from 
the pin(23) of IC701?
Check IC701.
Replace IC701.
NO
Check drum motor.
YES
YES
YES
YES
NO
NO
NO
D-FG
D-PG
YES
NO
YES
YES
NO
NO
FLOW CHART NO.16 HEAD SWITCHING PULSE TROUBLESHOOTING.
No head switching pulse.
See FLOW CHART NO.14, 15 (DRUM 
MOTOR TROUBLESHOOTING(1), (2))
Is the drum motor rotating?
Is the drum PG signal and drum FG 
signal present at pin(65) of IC701?
Replace IC701.
Check line between P701 and 
IC701.
Check peripheral circuit of IC on 
mechanism.
Are the drum PG signal and drum FG 
signal present on pin(11) of P701?
2.5V
2.5V
FLOW CHART NO.13 TIMER TROUBLESHOOTING
The LCD display fails to light up.
Is the supply voltage of 5V fed to 
pin(37) of IC8001?
Check AT 5V line.
Is the supply voltage of 3.4V, 1.7V 
feed to pin(38) and pin(39) of IC8001?
Check pin(38), (39) of IC8001 
and peripheral circuits.
Is it possible to confirm signals 
LCD RESET, LCD CS, LCD CLOCK
and LCD DATA on the pins(36),
(42), (43) and (44) of IC8001?
Are the segment signals 
supplied to the LCD display 
(LC8001) fromthe driver IC
(IC8001)?
Check peripheral circuit of pin(41) 
of IC8001.
Check that the LCD display is 
free from damages such as 
crack.
Replace IC8001.
YES
YES
YES
YES
NO
NO
NO
NO
NO
Check the signal line between
IC701 and IC8001.
YES
Is the OSC signal at pin(41) of 
IC8001 present?
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