YAMAHA YST-RSW300 ACTIVE SUB WOOFER DISASSEMBLING IDLE CURRENT ADJUSTMENT AND CIRCUIT DIAGRAM

YAMAHA YST-RSW300 ACTIVE SUB WOOFER DISASSEMBLING IDLE CURRENT ADJUSTMENT AND CIRCUIT DIAGRAM

YAMAHA YST-RSW300 

ACTIVE SUB WOOFER 

DISASSEMBLING IDLE CURRENT ADJUSTMENT AND CIRCUIT DIAGRAM 

DISASSEMBLY PROCEDURES

Disconnect the power cable from the AC outlet.
Spread a rubber sheet and cloth, then place the main unit upside down on it.

1. Removal of Front Grille Ass’y
# The front grille ass’y is fixed to the cabinet with dowels at 5 locations.
As a flatblade screwdriver is used for removal, use special care not to cause damage to the cabinet ass’y.
a. Using the flatblade screwdriver inserted in the gap between the front grille ass’y and the cabinet ass’y (bottom side first), push up the front grille ass’y. (Fig. 1)
b. Remove the front grille ass’y by lifting a metalblade up. (Fig. 1)
# When installing the front grille ass’y, apply quick-drying bond or the like to dowels and then fit them into dowel holes for secure installation. (The front grille ass’y will come off easily if its dowels are fitted into dowel holes without applying quickdrying bond or the like.)

2. Removal of Driver
a. Remove 4 screws (1)and then remove the driver. (Fig. 1)
b. Disconnect the connector connected to the terminal of the driver. (Fig. 1)

FIG-1

3. Removal of Rear Panel Ass'y
a. Remove 8 screws (2). (Fig. 2)
# Screws (2) are identified with arrow marks (<).
b. Pull out the rear panel ass'y together with the cover. (Fig. 2)
c. Remove bush. (Fig. 2)
# The bush once removed cannot be reused. Be sure to use a new bush for replacement.

d. Remove 2 screws (3). (Fig. 2)
# Screws (3) are identified with arrow marks (< ).
e. Remove the cover. (Fig. 2)
f. Disconnect the connectors (CB9 and CB10). (Fig. 2)

FIG-2

4. Removal of Front Panel Ass’y
# The front panel once removed cannot be reused. Be sure to use a new front panel for replacement.
Before installing the new front panel, be sure to remove the double sided adhesive tape remaining from the old front panel completely.
a. Remove 2 knobs (4). (Fig. 3)
b. Insert L-shaped metal parts or the like into the volume knob hole and high-cut knob hole in the front panel and pull the panel gradually away from the cabinet to remove it

c. Remove 2 screws (5). (Fig. 3)
d. Pull out the switch cover ass’y. (Fig. 3)
e. Remove bush. (Fig. 3)
# The bush once removed cannot be reused. Be sure to use a new bush for replacement.
f. Remove the switch cover ass’y together with the cable/ CB9. (Fig. 3)

FIG-3

When Checking the P.C.B.:
# Connect all the connectors removed during disassem bly back to the original positions.
# Spread cloth first and place the rear panel ass'y and switch cover ass’y on it. (Fig. 4)

FIG-4

CHECKS AND ADJUSTMENTS

Confirmation of power amplifier operation
For the power amplifier which has been repaired, it is absolutely necessary to confirm that a correct waveform is obtained at points indicated by A and B (FIG -5) in the schematic diagram according to the following procedure.

Devices required
Signal generator
8-ohm or 6-ohm load resistor
Oscilloscope (dual trace type)
Connection
1) Connect the output signal from the signal generator to the input terminal of the main unit.
2) Disconnect the connector terminal connected to the speaker unit and reconnect it to the load resistor.
3) Connect the HOT side of the oscilloscope CH1 probe to the point A or B indicated in the figure and the GND side to the GND of the main unit. (Fig. 1)
4) Connect the oscilloscope CH2 input to the red side of the connector cable, which is connected with the load resistor.
At this time, the GND terminal of CH2 must be left unconnected.

Setting
1) Set the signal generator to the sine wave, 100 Hz and minimum output level settings.
2) Set the volume of the main unit to the minimum position.
3) Turn on the power to the main unit.
4) Adjust the output level of the signal generator and the volume of the main unit so that the output level observed at oscilloscope CH2 is 26 Vp-p to 28 Vp-p.
Waveform observation
With the settings made as described above, observe the waveform obtained at CH1 for judgement.

Idling adjustment
To stabilize operation of the amplifier, turn ON the power with no input signal and wait for 2 to 3 minutes in non loaded condition before the adjustment.
Confirm that the voltage across the terminals TP1 and TP2 is 20 mV to 350 mV. If it exceeds 350 mV, open (cut off) R136.
Attention:
If the idling current exceeds 350 mV after a power amplifier repair, check for a defective component before cutting the resistor.

FIG-5

CIRCUIT DIAGRAM 

CLICK ON THE IMAGE TO ZOOM IN