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Hv Regulation Circuit Check And Adjustment; Hv Hold Down Circuit Operation Check And Adjustment - Sony RA-3B Service Manual

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G BOARD
3-1. HV REGULATION CIRCUIT CHECK AND
ADJUSTMENT
When replacing the following components marked with a Y on the
schematic diagram always check the HV regulation, and if necessary
re-adjust.
X :
C517
Y :
C517, C521, C522, IC654, L504, T502, T504 (FBT),
DY, A board, G board
OPERATION CHECK of 31.0KV +1.0 KV DC/ -2.5 KV DC
1. Connect an HV static voltmeter to the unused socket of the high-
voltage block. (Fig. 3-1)
2. Power on the set.
3. Display a dot pattern through the VHF/UHF input (PICTURE and
BRIGHTNESS set to minimum)
4. Check that the HV static voltmeter is reading
31.00 KV +1.0 KV DC / -2.5 KV DC.
HV Regulation adjustment
1. Connect a HV static voltmeter to the unused socket of the high-
voltage block.
2. Power on the set.
3. Display a dot pattern through the VHF/UHF input (PICTURE and
BRIGHTNESS to minimum).
4. If anode voltage is 31.95kV or higher, change the value of C517 from
470pF/2kV to 1,000pF/2kV, and confi rm that the high voltage is within
the range specifi ed above.
5. If anode voltage is 29.45kV or lower, change the value of C517 from
470pF/2kV to 100pF/2kV, and confi rm that the high voltage is within
the range specifi ed above.
Remove the cap from
the unused terminal and
connect a static voltmeter
here.
SECTION 3: SAFETY-RELATED ADJUSTMENTS
3-2. HV HOLD DOWN CIRCUIT OPERATION
CHECK AND ADJUSTMENT
When replacing the following components marked with a Y on the
schematic diagram always check the hold-down voltage and re-adjust
when necessary.
X :
R536, R545
Y : C516, C536, D506, D507, D522, IC206, IC502, IC654,
L504, R511, R522, R536, R538, R545, R548, R584, T502,
T504 (FBT), DY, A board, G board
OPERATION CHECK
1. Unplug connector CN652.
2. Connect an HV static voltmeter to the unused socket of the high-
voltage block.
3. Connect a 220Ω/200W resistor, across pin 2 and pin 1 of CN652,
and connect an external DC power supply (200V, class 2A) to pin
3 of CN652.
4. First, turn on the external power supply (+B=135V), then turn on the
power to the set.
5. Display a dot pattern through the VHF/UHF input (PICTURE and
BRIGHTNESS to minimum).
6. Gradually increase the value of the external DC power supply and
check that the hold-down circuit operates at a static HV voltmeter
reading of 33.5±1.0kVdc when the set shuts down.
7. Remove AC power from the set, then remove the 220Ω/200W resistor
and reconnnect CN652.
HV HOLD-DOWN ADJUSTMENT
1. Repeat steps 1-8 above.
2. If hold-down voltage is 34.5kV or higher, remove R536, mount a
resistor (150kΩ, 1/4W : RN) onto R545 instead, and check again if the
hold-down voltage is within the standard range.
3. If hold-down voltage is 32.5kV or lower, mount a resistor (220kΩ,
1/4W : RN) onto R536 and check again if the hold-down voltage is
within the standard range.
NOTE: Finish the adjustment as soon as possible.
— 25 —
KP- 43T90 / 48V90 / 53V90 / 61V90

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