Troubleshooting Power Supply Unit Vfm (B, G) - Yamaha DVD-S520 Service Manual

2. TROUBLESHOOTING POWER SUPPLY UNIT VFM (B, G)

Check DC voltages
+12V, +5Vstdby, -5V, +5V, +3V3
Disconnect the power supply from the MAIN Board
Connect dummy load resistors 10W ( min 5W ) :
10 ohm at +3V3, 15 ohm at +12V and ground
Check DC voltages
+12V, +5Vstdby, -5V, +5V, +3V3
These voltages will be somewhat higher than specified
Check the +3V3 and +12V
Check +12V path : D6241, C2240, L5240
Check +3V3 path : D6210, C2210, L5210
Connect the mains inlet to a mains isolated variac
Turn input voltage up and check across C2121
the voltage should be
+/-1.41 X Vin AC
Is power supply ticking?
Check supply voltage on pin 7 of IC7145
Vcc within 10V - 16V (typical )
Power Supply Unit
START
NOK
NOK
NOK
OK
OK
NO
OK
OK
OK
Power Supply
OK
Power Supply OK
OK
• Check : Mono Board
A/V Mux Board
Display Board
OK
• Check the path of the faulty voltages:
+5V path: D6230, L5231,T7235, C2230, C2238, C2239
-5V path: D6250, C2250, L5222,T7257 and T7255
regulator unit
+5V_stby path: R3233, D6233
Check standby control at pin 10 of conn. 0205
Standby ON: 5.0V +/- 0.5V
Standby OFF: 0V
NOK
• Check the functionality of the following components:
F1120, L5120, D6118, D6119, D6120, D6121, C2121
YES
• Check the load on the secondary output
• Check overvoltage protection:
D6141, R3139,T7141,T7150, R3150
• Check oscillator voltage on pin 4 of IC7145
• Check R3146,C2157 and replace IC7145
• Check drive circuit : gate voltage of Mosfet 7125,
components R3111, R3140, R3156,R3125,D6140
• Check working of regulation circuit :
T7131,T7201,R3201,R3202,R3204,R3205,
R3206,R3207,R3208,R3153,R3154,R3262,C2202
NOK
• Check start-up circuit and Vcc supply circuitry
Replace IC7145
DVD-S520/DV-S5450
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