Service manual

39
VC-A410U
VC-H810U
7. TROUBLESHOOTING
FLOW CHART NO.1
No power
The fuse blows out even when it is replaced with new one. See FLOW CHART NO.2 <Fuse blown out.>.
YES
YES
YES YES
NO
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. (L901, D901~904, T901, C906, R904, Q901~902, etc.)
Are AT 5V voltage line normal?
Are AT 44V, AT 23V, PC 12V, AT –24V and filament voltage lines normal?
Check each rectifier circuits and short-circuit of secondary circuit.
Is "H" level applied at pin(1) of IC701?
Check the power failure circuit. (Q705)
FLOW CHART NO.3
When the output voltage fluctuates.
Check whether the secondary side photocoupler circuit operates normally.
Check the circuit and replace parts. (IC901, IC903, etc.)
NO
YES
Check whether the primary side photocoupler output control functions normally.
Check the circuit and replace parts. (IC901, IC903, Q902, T901, etc.)
NO
YES
Replace IC901.
FLOW CHART NO.2
Fuse blown out.
Case (1) Case (2)
Check for leak or short-circuiting of primary circuit part. (L901, D901~904, T901, C906, R904, Q901~902, etc.)
Check for short-circuiting of rectifying diode and circuit in each rectifying circuit of secondary circuit. (D921~928)
FLOW CHART NO.4
When buzz is heard from the vicinity of power circuit.
Check for short-circuiting of circuit and rectifying diode of each rectifying circuit of secondary circuit and check for failure of shunt regulator circuit. (D921~928, IC903, C932, C933)
FLOW CHART NO.5
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(87) and (88) of IC701?
Check or place the peripheral circuit of IC701.
YES
YES
NO
Key-in input is not received.