Sony STR-DE845 Training Manual page 36

Power Supply is Dead
Normally when you press the front panel ON switch, the CPU (on the DVD board) is powered with 5.6Vdc. The
unit can then power ON when you press either the front panel Play or one of the five Eject buttons. The display
will then illuminate, showing the unit's model number and then the input mode - "DVD".
In the following steps, you will verify the voltages necessary to sustain the oscillator operation. You must use an
isolation transformer and be cautious when probing the components to avoid shorting parts. First, locate the
hot and cold grounds using Figure 9-5.
1. Plug the unit into AC and press the front panel Power button IN (should latch in).
2. Measure the PS Output voltage at CN904/pins 1 or 2 (normally 19Vdc in this Standby Mode). Refer to Figure
9-5 to locate the cold ground for this voltage measurement.
• NO voltage - proceed to step 3 (next). The power supply is dead.
• 19V is present - Go to step 8. The power supply is running in standby mode but may not power ON.
3. Verify 163Vdc from the bridge rectifier at either end of 9.1-ohm TH901. Use the HOT ground at R902 (Fig 9-
5).
4. This 163Vdc should pass through T901's primary winding and appear at IC901/pin 3, which is inaccessible
from the top. Check for this voltage at the lead of C916 nearest R903. Use HOT ground at R902 (Fig 9-5).
5. Verify about 60Vdc and 24Vdc at the two leads of R908. This is the lower voltage from the bridge rectifier
D902, reduced by R908. Use the HOT ground at R902 (Fig 9-5).
6. This voltage should be regulated by Q901-Q903 down to 11Vdc at IC901/pin 4 in this Standby Mode (20Vdc
when the unit is ON). Use the HOT ground at R902 (Fig 9-5).
7. If these voltages in steps 1-6 are present, IC901 should be oscillating, producing the two Standby Mode
voltages listed in Chart 9-5. Use the cold ground at D909's heat sink (Fig. 9-5). If the two standby voltages
are present, the standby section of the supply is OK, the problem is that the power supply will not turn ON (go
to step 9). If the supply voltages are missing, the power supply is in protection (next step 8) or the oscillator
(IC901) is defective.
CN904/pin 1, 2
CN905/pin 1
CN905/pin 2
CN905/pin 3
CN905/pin 4
8. If there are still no standby output voltages, the power supply may have started and gone into protection.
When the front panel power button is pressed and the oscillator at IC901/pin 3 (actually scope probed at
C916) appears (as bursts), then stops, IC901 is in protection. An incorrect voltage input to IC901/pin 1 could
cause this. An applied voltage above or below 0.8-4Vdc will stop the oscillator. This operating voltage comes
from the regulator parts PC901, D912 and IC902 – all of which must be checked.
Power Supply will not Power ON
9. If both standby voltages are present (see Chart 9-4), the power supply works in standby but will not power
ON, causing the dead power supply symptom. Check for a normal 5.6Vdc (reset) from the power supply to
the CPU at CN905/pin 9. Zero volts inhibit the CPU (held at reset) so the CPU cannot turn the power supply
ON. This reset line (not shown) comes from the power supply board.
10. P Cont 1 at CN905/pin 10 should change from 0Vdc (standby) to 4.7Vdc (ON) when the front panel PLAY or
any Eject button is pressed. Measure P Cont 1 at CN905/pin 10. If this voltage:
Chart 9-4 - Power Supply Output Voltages – Use Cold Ground
Location Standby Mode
19Vdc
0.22Vdc
0.08Vdc
0V
5.6Vdc
9. DAV-C700 Switching Type Power Supply
Power ON Mode
27Vdc
13.6Vdc
6.4Vdc
3.3Vdc
5.6Vdc
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