Bose 300PM User manual

®
®
MODEL 300PM LOUDSPEAKER
Part Number 193626 Rev. 00
Service Manual
©1997 Bose Corporation

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
BYANAUTHORIZED BOSE SERVICE CENTER OR OWNER OF THE
BOSE PRODUCT, AND SHALLNOT BE REPRODUCED OR USED
FORANY OTHER PURPOSE.
CONTENTS
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
Note: This service manual has been updated with information from supplement
193626-S2, affecting part numbers for PTC1 and PTC2.

3
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 octave-
band 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: 6ΩNominal, 4.8Ωminimum 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

4
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.

5
DISASSEMBLY/ASSEMBLY PROCEDURES
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.
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.

6
DISASSEMBLY/ASSEMBLY PROCEDURES (CONT.)
6.4 Gently slide the crossover assembly
onto the tabs on the binding post connector
until it is seated.
6.5 Secure the crossover assembly using
the four screws (8) removed in
procedure 5.
6.6 Replace the batting removed in
procedure 5.2.
6.7 Replace the driver (3) and grille (1)
using procedure 4.
7. Binding Post Connector removal
7.1 Remove the grille (1), driver (3), and
crossover assembly (9) using procedure 5.
7.2 Remove the four screws (2) that
secure the binding post connector (10) to
the speaker cabinet.
7.3 Gently pull on the binding post
connector housing until it comes free of the
cabinet.
8. Binding Post Connector replacement
8.1 Slide the binding post connector (10)
into the rear of the cabinet. Be sure it is
oriented so that the + and - markings on
the binding post connector are nearest the
edge of the cabinet.
8.2 Secure the binding post connector to
the cabinet using the four screws (2)
removed in procedure 7.2. Be sure not to
overtighten the screws, or you will crack the
binding post connector housing.
8.3 Reinstall the crossover assembly (9),
driver (3), and grille (1) using procedure 6.

7
Figure 1. Model 300PM Loudspeaker test
setup diagram
Note: Refer to Figure 2. Model 300PM
driver wiring diagram for the following
procedure.
1. Phase Test
1.1 Remove the speaker grille using
Disassembly/Assembly procedure 1.
1.2 Observing polarity, apply a +6Vdc level
to the input terminals on the rear of the
loudspeaker. The drivers should both
move outward.
1.3 Replace the grille using procedure 2.
Note: Refer to Figure 1. Model 300PM
Loudspeaker test setup diagram, for the
following tests.
2. Rub and tick test
2.1 Remove the grille using procedure 1.
2.2 Apply a 6Vrms, 10Hz signal to the
input terminals on the rear of the speaker
cabinet.
2.3 Listen carefully for any buzzes, rattles,
or other extraneous noises from the drivers
or trim parts.
Note: There is a normal suspension noise.
To distinguish between a rub or a tick and
suspension noise, displace the driver cone
slightly with a finger. If the noise stays the
same, it is suspension noise.
2.4 Replace the grille using procedure 2.
3. Air Leak Test
3.1 Remove the grille using procedure 1.
3.2 Apply a 6Vrms, 60Hz signal to the
input terminals on the rear of the speaker
cabinet. Leave the speaker port open.
3.3 Test duration should be 5 seconds
minimum.
3.4 Listen carefully for air leaks along all
glue joints, at the binding post connector,
and at both transducer mounting locations.
Air leaks will be heard as a hissing or
sputtering sound. All repairs must be
hidden.
3.5 Replace the grille using procedure 2.
4. Power Sweep Test
4.1 Apply a 6Vrms, 10Hz signal to the
input terminals on the rear of the speaker
cabinet. Leave the speaker port open.
4.2 Sweep the input frequency from 10Hz
to 3kHz.
4.3 Reduce the input voltage level to
4Vrms and sweep the oscillator from 3kHz
to 5kHz.
Note: The whooshing noise from the port
at approximately 60Hz is acceptable.
4.4 Replace any transducer that has a
buzzing noise. There shall not be any
buzzes or rattles from the internal
connecting wires or components.
Redress any buzzing wires.
TEST PROCEDURES
Power Amplifier
Frequency
Generator
Loudspeaker
+ -
+- +-
+
-
-
+DMM

8
_+
RED
BLACK
DRIVER
DRIVER
PCB
BLUE
-+
Figure 2. Model 300PM Loudspeaker driver wiring diagram

9
Figure 3. Model 300PM Loudspeaker schematic diagram
- OUTPUT
- INPUT
(BLACK)
+ OUTPUT
(RED)
+ INPUT
TO
ANGLED
DRIVER
TO
FRONT
DRIVER
(BLUE) (BLUE)
0V
+6.8V
PTC2
(0.4A,1.3 OHM)
RXE040
PTC1 (0.25A, 3.0 OHMS)
RXEO25
Q10
2SC536K-E
Q52SC536K-E
Q2
2SC536K-E
Q3
2SC536K-E Q4 2SC536K-E
Q6
2SA608K-E
Q1
2SA608K-E
3
2
1
Q7
IRLI540G
G
S
D
L1
65uH
1
W5
1
W6
R16
2K 1W
R15
0.15
2W
R11
1.5K R13
1.5K
R12
1.5K R14
1.5K
R6
51K
R9
51K
R10
100K
R8
560
R7
51K
R4
20K
R3
20K
R2
1.0M
D3
1N4736
3
2
1
Q8
IRLI540G
GS
D
Q9
2SA608K-E
C7
10/25V
C6
10/25V
C3
100/25V
C4
100pF
C2
0.33/250V
D9
1N4148
D8
1N4148
D7
1N4148
D6
1N4148
D4
1N4148
D1
1N3070
C5
0.27
C8
10/50V
C1
0.33/100V
D2
1N3070
D5
1N4148
R19
51K
R20
100K
R21
10K
R5
51K
R18
200
R1
40K
1W
R17
20K
1W41
W2
1
W3
1W1
Notes: Unless otherwise specified 1. Resistor values are in Ohms.

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

12
Model 300PM Loudspeaker crossover assembly part list (per figures 4&5)
Reference
Designator Description Part Number Qty per Assy.
R1 Res, Metal Oxide, 1W, 5%, 39KΩ171259-3935 1
R2 Res, CF, 1/4W, 5%, 1 MEGΩ120968-1055 1
R3, R4, R17 Res, CF, 1/4W, 5%, 20kΩ120968-2035 3
R5, R6, R7, R9, R19, Res, CF, 1/4W, 5%, 51kΩ120968-5135 5
R8 Res, CF, 1/4W, 5%, 560Ω120968-5615 1
R10, R20 Res, CF, 1/4W, 5%, 100kΩ120968-1045 2
R11, R12, R13, R14 Res, CF, 1/4W, 5%, 1.5kΩ120968-1525 4
R15 Res, Metal Oxide, 2W, 5%, .15Ω177962-R155 1
R16 Res, Metal Oxide, 1W, 5%, 2kΩ171259-2025 1
R18 Res, Fusing, 1/4W, 5%, 200Ω130102-2015 1
R21 Res, CF, 1/4W, 5%, 10kΩ120968-1035 1
C1 Cap, Film, 85, 100V, 5%, .33uF 120388-334 1
C2 Cap, Box, 85, 250V, 10%, .33uF 190483-334 1
C3 Cap, El, 85, 25V, 20%, 100uF 119941-101E 1
C4 Cap, Disc, SL, 50V, 10%, 100pf 137269-101 1
C5 Cap, Box, 85, 50V, 5%, .27uF 137127-274 1
C6, C7 Cap, El, BP, 85, 25V, 20%, 10uF 149948-100E 2
C8 Cap, El, BP, 85, 50V, 20%, 10uF 138365 1
L1 Inductor, 65 uH, .11 Ohm, Ferrite 189799 1
D3 Diode, Zener, 6.8V, 1W, 5%,
1N4736 116995-4736A 1
D4, D5, D6, D7, D8,
D9 Diode, Switching, 75V, 300mA 1N4148 121501 6
Q2, Q3, Q4, Q5, Q10 Transistor, Bi-polar, N, 60V, 200mA,
TO-92, 2SC536K-E 117921 5
Q1, Q6, Q9 Transistor, Bi-polar, P, 60V, 200mA,
TO-92, 2SA608K-E 119168 3
D1, D2 Diode, Glass, 200V, .5W, 1N3070 190346 2
Q7, Q8 N-Channel, Hexfet, IRL1540G 190347 2
PTC1 Polyswitch, 60V, 4mm 190348-1 1
PTC2 Polyswitch, 60V, 4mm 191995-1 1
W5,W6 Connector, Terminal, 1 Pos, Female 147946 2
used with L1 Screw, Machine, 4-40x1, Pan, Xrec 103146-16 1
used with L1 Nut, Hex, 4-40 103234-440 1
used with L1 Washer, Flat, .141, #5 108258-05 1
PCB, Bare Board, 300PM 187255-001 1

13
Model 300PM Loudspeaker part list (per figure 6)
Figure 6. Model 300PM Loudspeaker exploded view
REF
6
LOGO NOT SHOWN
(2X)
(4X)
(4X)
(2X)
(2X)
(4X)
(3X)
(3X)
REF
REF
1
2
3
2
4
5
7
5 6 7
9
8
2
10
5 6 7
Item
Number Description Part Number Quantity per Assembly
1 Grille Assembly, 300PM 187239-001 1
2 Screw, Tapp, 8-11x.75,Pan, Xrc/Sq 172672-12 10
3 Driver Assembly, Shielded, 4.5” 187246-001 2
4 Grommet, Grille Socket 176068 4
5 Insert, Threaded, Ext/Intl 121690 4
6 Washer, Lock, .326, 5/16, Intl T 121692-31 4
7 Nut, Lock, Flange, M8 121691 4
8 Screw, Hilo, 6x.375, Pan/Xrec 175972-06 4
9 Crossover Assembly, 300PM 187241-001 1
10 Connector, Binding Post, 203, Grey 187232-003 1
- Nameplate, Logo, Black 187254-001 1

14
Model 300PM Loudspeaker packing part list (per figure 7)
Item
Number Description Part Number Quantity per Pair
1 Packing, End Cap, 203 187243-001 2
2 Bag,Poly, 13.5x33.5x13x3 mil 106595 2
3 Carton, RSC, 300PM 187242-001 1
Figure 7. Model 300PM Loudspeaker packing diagram
(2X)
1
2
1
3

15
Model 300PM Loudspeaker Accessories
There are three optional brackets that can be used to mount the Model 300PM Loudspeaker
that are available through Bose BKK. They are model numbers CB-22, GWS-200, and GBB-1.
Note: All measurements are in millimeters; all angles are in degrees.
Figure 8. CB-22 bracket
Figure 9. GBB-1 bracket
Figure 10. GWS-200 bracket

SPECIFICATIONS AND FEATURES SUBJECT TO CHANGE WITHOUT NOTICE
®
®
P/N 193626 REV. 00 08/97 FOR TECHNICALASSISTANCE OR PART ORDERS, CALL1-800-367-4008
Bose Corporation
The Mountain
Framingham, Massachusetts, USA 01701