Panasonic SAHT730 Technical Guide - Page 18

Subwoofer Repair Procedure

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Follow this procedure to determine if the Subwoofer causes shut down: Refer to the subwoofer protection simplified troubleshooting circuit, in figure 12. Disassembly and service positions are shown in figures 13 and 14. 3. Do not connect the Control unit to the Subwoofer. On the larger power board of the subwoofer, tack a 10k ohm test resistor across D508 to serve as a temporary "DC Det" pull-up resistor so that the subwoofer can be tested alone. 4. Jump the contacts of the AC relay RLY501. 5. While monitoring the unbanded anode end of D508 with your DC voltmeter, momentarily plug the subwoofer into AC. 6. If the voltage remains at 0Vdc, unplug the AC immediately. The problem is in the subwoofer. See subwoofer repair below. 7. If the voltage rises to 7-9Vdc, the problem is in the Control unit, not this subwoofer. Disconnect the test resistor and close the subwoofer. Subwoofer Repair Procedure 1. Refer to figure 12. To supply pull-up voltage, either leave the 10k ohm test resistor across D508 or plug in the control unit, but Do not do both. 2. On the SB-WA930 Subwoofer, remove the Front Amp board. See subwoofer disassembly diagrams figures 13 & 14. 3. If RLY501 contacts are shorted, momentarily plug the subwoofer into AC while monitoring the unbanded anode end of D508 with your DC voltmeter. If the control unit is connected, press its power-on button while measuring the D508/A voltage. • Voltage remains at 0Vdc - the problem is on the subwoofer's power amp board. Remove Q501/Q502, Q559, and Q556/Q557 one group at a time to determine which group permits D508/Anode voltage to rise to 5-9V when plugged in momentarily. If removing a group of transistors causes D508/A voltage to rise, the feed for those transistors is at fault. E.g. If Q501/2 was removed, and the voltage came up to 5-9V, suspect IC501 and the transistors removed (Q501 & Q502). • Voltage rises to 5-9Vdc (normal voltage): SB-WA930 - the problem is in the Amp board that was unplugged or the + supply voltage from T501 (H601) is unbalanced (+V not = -V). Check for open foils to connector H601 and replace IC601 on the board. SB-WA730 - The problem is not in the subwoofer. Check the control unit. 4. Remove the 10k ohm test resistor across D508 to prevent micro damage. SA-HT730 / SAHT930 18

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SA-HT730 / SAHT930
18
Follow this procedure to determine if the Subwoofer causes shut down:
Refer to the subwoofer protection simplified troubleshooting circuit, in figure 12.
Disassembly and service positions are shown in figures 13 and 14.
3. Do not connect the Control unit to the Subwoofer.
On the larger power board of
the subwoofer, tack a 10k ohm test resistor across D508 to serve as a temporary
“DC Det” pull-up resistor so that the subwoofer can be tested alone.
4. Jump the contacts of the AC relay RLY501.
5. While monitoring the unbanded anode end of D508 with your DC voltmeter,
momentarily plug the subwoofer into AC.
6. If the voltage remains at 0Vdc, unplug the AC immediately.
The problem is in the
subwoofer.
See subwoofer repair below.
7. If the voltage rises to 7-9Vdc, the problem is in the Control unit, not this
subwoofer.
Disconnect the test resistor
and close the subwoofer.
Subwoofer Repair Procedure
1. Refer to figure 12.
To supply pull-up voltage, either leave the 10k ohm test
resistor across D508 or plug in the control unit, but
Do not
do both.
2. On the SB-WA930 Subwoofer, remove the Front Amp board.
See subwoofer
disassembly diagrams figures 13 & 14.
3. If RLY501 contacts are shorted, momentarily plug the subwoofer into AC while
monitoring the unbanded anode end of D508 with your DC voltmeter.
If the
control unit is connected, press its power-on button while measuring the D508/A
voltage.
•
Voltage remains at 0Vdc - the problem is on the subwoofer’s power amp
board.
Remove Q501/Q502, Q559, and Q556/Q557 one group at a time to
determine which group permits D508/Anode voltage to rise to 5-9V when
plugged in momentarily.
If removing a group of transistors causes D508/A
voltage to rise, the feed for those transistors is at fault.
E.g. If Q501/2 was
removed, and the voltage came up to 5-9V, suspect IC501 and the transistors
removed (Q501 & Q502).
•
Voltage rises to 5-9Vdc (normal voltage): SB-WA930 - the problem is in the
Amp board that was unplugged or the +
supply voltage from T501 (H601) is
unbalanced (+V not = -V).
Check for open foils to connector H601 and
replace IC601 on the board.
SB-WA730 – The problem is not in the
subwoofer. Check the control unit.
4.
Remove the 10k ohm test resistor across D508
to prevent micro damage.