Philips CDR779 Service Manual page 62

GB 62 8.
When the regulation circuit is interrupted due to an error in
the control loop, the regulated output voltage will increase
(overvoltage). This overvoltage is sensed on the primary
winding 7-9. When an overvoltage longer than 2.0µs is
detected, the output is disabled until Vcc is removed and then
re-applied. The power supply will come in a hiccup mode as
long as the error in the control loop is present.
8.2.8 Troubleshooting PSU CDR3-ECO
Faultfinding diagram
TROUBLE SHOOTING POWER SUPPLY
CDR779 Faultfinding Guide
Check DC voltages
+5V +12V -8V VFTD(-38V) VDC1-VDC2(3V8)
NOK
Disconnect the power supply from the MAIN Board
Connect a dummy load resistor 6,8 ohm 10W (min 5W)
on the 5V and
Check DC voltages
+5V +12V -8V VFTD(-38V) VDC1-VDC2(3V8)
NOK
Check the +5V
NOK
connect the mains inlet to a mains
isolated variac
turn input voltage up and check across
C2121 the voltage
this voltage should be +/- 1,41 x Vin ac
OK
is power supply ticking?
NO
check Vcc on pin 7 IC7110
Vcc = 12V...... 16V
OK
check oscillator on pin 4 IC7110
is the osc +- 30kHz working ?
OK
check the voltage on the source of 7125
Vsource = 1,3V ?
NO (Vsource = +- 0.8V)
Disconnect diode 6150
start variac from 0V and turn-up slowly
measure the 5V output
If the 5V becoming higher than 5V, the regulator
circuit are damaged
5V OK
After the power repaired check the 3,3V
Secondary rectifier/smoothing circuit
There are 5 rectifier/smoothing circuits on the secondary
side. Each voltage depends on the number of windings of the
transformer.
The -8V supply is regulated by voltage regulator 7249.
On/off circuit
In off mode pin 1 and pin 2 of connector 0206 are connected.
The high voltage (-8V, +12V) over opto coupler 7200 forces
this one to conduct . IC 7110 is switched off
OK
power supply OK
power supply OK
OK
check - main board
- front board
- modem board
OK
check the fault voltage path
check 6210-2210-2253-5210
OK
NOK
check the functionality of the following components:
1120-2121-2125-2126-2127-6102-7125
YES
check the load on the secundairy output
check overload circuit 6141-7141-7150
NOK
check 2121-2133-2134-3123-3134-6130-6132
replace 7110
NOK
check 2102 - 3102
replace 7110
check 3125-3126-3127-3128
YES
replace 7125
check:3201-3202-3203-3204-3205
5V NOK 3206-3207-3208-7131-7201
replace 7110
check circuit around Ic7110
Figure 8-16
CL 06532151_024.eps
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