BOSE 300 PM Schematic
MODEL 300PM LOUDSPEAKER
®
®
©
1997 Bose Corporation
Service Manual
Part Number 193626 Rev. 00
CONTENTS
Note: This service manual has been updated with information from supplement
193626-S2, affecting part numbers for PTC1 and PTC2.
Specifications......................................................................................................................3
SmartProtect Crossover PCB operation and troubleshooting ....................................... 4
Disassembly/Assembly procedures...............................................................................5-6
Test procedures .................................................................................................................. 7
Figure 1. Model 300PM Loudspeaker test setup diagram .............................................................. 7
Figure 2. Model 300PM Loudspeaker driver wiring diagram........................................................... 8
Figure 3. Model 300PM Loudspeaker schematic diagram.............................................................. 9
Figure 4. Model 300PM Loudspeaker Crossover Assembly top side etch layout diagram ........... 10
Figure 5. Model 300PM Loudspeaker Crossover Assembly bottom side etch layout ................... 11
Model 300PM Loudspeaker crossover assembly part list (per figures 4&5)............... 12
Model 300PM Loudspeaker part list (per figure 6) ......................................................... 13
Figure 6. Model 300PM Loudspeaker exploded view ................................................................... 13
Model 300PM Loudspeaker packing part list (per figure 7) ..........................................14
Figure 7. Model 300PM Loudspeaker packing diagram................................................................ 14
Model 300PM Loudspeaker Accessories........................................................................ 15
Figure 8. CB-22 bracket ................................................................................................................ 15
Figure 9. GBB-1 bracket ............................................................................................................... 15
Figure 10. GWS-200 bracket ........................................................................................................ 15
CAUTION: THE MODEL 300PM LOUDSPEAKER CONTAINS
NO USER-SERVICEABLE PARTS. TO PREVENT WARRANTY
INFRACTIONS, REFER SERVICING TO WARRANTY
SERVICE STATIONS OR FACTORY SERVICE.
PROPRIETARY INFORMATION
THIS DOCUMENT CONTAINS PROPRIETARY INFORMATION OF
BOSE® CORPORATION WHICH IS BEING FURNISHED ONLY FOR
THE PURPOSE OF SERVICING THE IDENTIFIED BOSE PRODUCT
BY AN AUTHORIZED BOSE SERVICE CENTER OR OWNER OF THE
BOSE PRODUCT, AND SHALL NOT BE REPRODUCED OR USED
FOR ANY OTHER PURPOSE.
SPECIFICATIONS
External Dimensions: 12.83"L x 8.43"D x 7.25"H
(32.6cm x 21.4cm x 18.42cm)
Internal Cabinet Volume: 5.7 Liters (347 cu.in.) net
Sensitivity (1W, 1m): 83.8dB SPL (calculated), free
field, per IEC-268-5 (for octaveband centered at 400Hz).
SmartProtect Circuit characteristics:
Turn-on voltage of the transistors of the electronic switch: 1.5-1.8 Vrms
Turn-on level rise: 2-6 dB
On resistance: <0.33Ω
Maximum audio voltage applied to speaker: 60 Vrms
Maximum continuous sinusoidal current: 3.4 Arms ±15%
Reset Time: 250-300 ms
Port (each side): Flared slot port tuned to 60Hz.
Impedance: 6Ω Nominal, 4.8Ω minimum from
20Hz to 20kHz.
Power Handling: 100W (24.5 Vrms) continuous
600W peak power handling
w/SmartProtect circuit
Weight: 12.5 lb (5.7 kg) each
Shipping Weight: 28 lb (12.7 kg) per packed pair
3
SmartProtect Crossover PCB operation and troubleshooting
Note: Refer to Figure 3. Model 300PM Loudspeaker schematic diagram, for
the following information.
The SmartProtect PCB is an electronic switch, in series with the drivers, used
to protect the drivers from high current levels. It has a fast turn-on time of 100
milliseconds. At turn-on, current will flow through R16, R15, C2, D1, D2, C1,
and R18. C2 and C3 form a virtual power supply which is used to provide
operating voltage for the circuit as well as the bias for Q7 and Q8. This bias is
limited by the zener diode D3 to 6.8 V. D1 and D2 form a voltage doubler.
Once C2 is charged, Q9 will conduct and provide a charge path for C3. Once
C3 is charged and the input audio voltage becomes lower than 1.5 Volts, Q9
will turn off. With Q9 shut off, the charge on C3 provides a voltage used to
operate the circuit for up to 5 hours.
R15 is a current sensing resistor. If current levels through it are too high, it will
turn on either Q3 or Q4. This will pull the base of Q1 to the virtual ground,
tripping the monostable multivibrator formed by Q1 and Q2. This will provide a
250 to 300 millisecond positive pulse to the base of Q5, turning it on for that
amount of time. While Q5 is conducting, it will apply 0 Volts to the gates of Q7
and Q8, shutting them off and disabling the loudspeaker for that amount of time.
Once the charging of C5 through R2 is completed, Q5 will shut off again, turning
Q7 and Q8 back on, and allowing the speaker to operate again. If the overload
condition persists, it will trip the circuit again after about 10 ms, shutting off the
drivers again.
Troubleshooting
1. If PTC1 is open, the unit will not play at low volume levels (Vin < 1.5 Volts)
when the system is first turned on, but as the volume is increased, the
SmartProtect circuit will turn on, and the speaker will operate. It will then
operate for 5 hours, until the charge on C3 is too low to keep the circuit running,
and then the speaker will shut off again.
2. If either R18 or R16 is open, there will be no charge path for the virtual power
supply formed by C2 and C3, and the circuit will never turn on. The symptom
will be that the speaker will play at low volume levels (Vin < 1.5 Volts), but as
the volume is turned up, the speaker will stop operating. This may also happen
if for any reason Q7, Q8 or any other component in the circuit fails, and the
internal safety “watchdog” C7 turns the Q5 on preventing the Q7 and Q8 from
being overheated.
4
DISASSEMBLY/ASSEMBLY PROCEDURES
Note: Refer to Figure 6 for the following
procedures.
1. Grille removal
1.1 Using your fingers, grasp the grille (1)
edge nearest the port slot and gently pull
the grille away from the cabinet until it
comes free.
1.2 Grasp the opposite edge of the grille
and gently pull it away from the cabinet
until it comes free as well.
2. Grille replacement
2.1 Orient the grille (1) so that the Bose
logo is aligned with the print on the rear of
the cabinet.
2.2 Align the two grille posts on the curved
grille edge with the cabinet grille socket
grommets (4) and press the grille edge in
place.
2.3 Align the two grille posts at the
opposite grille edge with the cabinet grille
socket grommets and press the grille in
place. The grille should be neat and flush
with the cabinet.
3. Driver removal
3.1 Remove the grille (1) using
procedure 1.
3.2 Using a phillips-head screwdriver,
remove the three screws (2) that secure the
driver (3) to the cabinet.
3.3 Using your fingers, grasp the plastic
basket of the driver and pull gently. The
driver should come free.
3.4 Note the driver wiring color code, and
cut the wires as close to the terminals as
possible.
4. Driver replacement
4.1 Observing polarity, solder the wires
from the crossover assembly (9) to the
driver (3) terminals.
4.2 Orient the driver correctly into the
cabinet and secure it using the screws (2)
removed in procedure 3.2.
4.3 Replace the grille (1) using
procedure 2.
5. Crossover Assembly removal
®
5.1 Remove the driver (3) located behind
the curved portion of the grille (1) using
procedure 3. Do not cut the wires to the
driver.
5.2 Remove the batting behind the driver
and retain it to reinstall later.
5.3 Using a long shaft phillips-head
screwdriver, remove the four screws (8)
that secure the crossover assembly (9) to
the binding post connector (10).
5.4 Gently pull the crossover assembly
straight off of the metal tabs on the binding
post connector until it comes free. You can
now slide the crossover assembly out
through the driver opening.
5.5 Unsolder the wires from the crossover
assembly.
6. Crossover Assembly replacement
6.1 Solder the driver (3) wires to the
appropriate locations on the crossover
assembly (9).
6.2 Insert the crossover assembly through
the driver opening.
6.3 Orient the crossover assembly so that
the tabs on the binding post connector (10)
and the receptacles on the crossover
assembly are aligned.
5
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