BOSE 251 ENVIRONMENTAL SPEAKER – DISASSEMBLING AND REASSEMBLING - TEST PROCEDURE – WIRING DETAILS – SCHEMATIC DIAGRAM – AUDIO SYSTEM REPAIR AND SERVICE

BOSE 251 Environmental Speaker – Disassembling and reassembling - Test Procedure – Wiring details – Schematic diagram – Audio system repair and service

Category: Audio System Repair and Service 

Contents of this article 

• Disassembling and Reassembling
• Test procedure
• Schematic diagram  

BOSE 251 Environmental Speaker

DISASSEMBLY/ASSEMBLY PROCEDURES

1. Grille and Baffle Removal
1.1 Grasp the edge of the grill (5) and pull it off.
1.2 Remove the six screws (13) that secure the baffle to the cabinet and then pull off the baffle.
2. Grille and Baffle Replacement
2.1 To prevent air leaks, apply a new baffle woofer mount gasket (10). To prevent wire buzzes, insert the wires into the cabinet’s wire channel. Line up the baffle so that the baffle’s woofer mount fits into the groove in the cabinet. Replace the six screws (13) that secure the baffle to the cabinet.

2.2 Align the grille (5) with the cabinet so that the logo (6) is over the Twiddlers (2). Press the grille into place.
3. Twiddler Removal.
3.1 Perform procedure 1.1.
3.2 Remove the four screws (12) that secure the Twiddler (2) to the cabinet.
3.3 Lift the Twiddler out and cut the wires as close as possible to the wire terminal.
Note: Make a note of the wiring configuration.
4. Twiddler Replacement
4.1 Referring to the note taken in 3.3, attachthe wires to the Twiddler (2).

4.2 Line up the Twiddler™ in the cabinet and replace the four screws (12) that secure the
Twiddler in place.
5. Woofer Removal
5.1 Perform procedure 1.
5.2 Cut the wires as close as possible to the woofer’s (1) wire terminal.
5.3 Remove the four screws (12) that secure the woofer to the baffle. Lift the woofer out.
6. Woofer Replacement
6.1 To prevent air leaks, apply a new gasket (11) to the woofer. Line up the woofer (1) in the baffle so that the wire terminal is facing toward the Twiddlers (2). Replace the four screws (12) that secure the woofer to the baffle.
6.2 Attach the green and black wires to the negative terminal and the red and yellow wires to the positive terminal of the woofer.
6.3 Place the foam tape gasket (10) around the edge of the baffle’s woofer mount where it contacts the cabinet.
7. Protection Circuit Removal
7.1 Perform procedure 1.
7.2 Cut the wires as close as possible to the leads of the polyswitch (3).
8. Protection Circuit Replacement
8.1 Connect the leads of the polyswitch (3) to the wires and solder the connections. The polyswitch is wired in series with the speaker’s positive terminal and the woofer’s (1) positive terminal..
9. Crossover Capacitor Removal
9.1 Perform procedure 1.

9.2 Remove the four screws (12) that secure the Twiddler panel (15) to the baffle. Pry off the panel.
9.3 Cut the wires as close as possible to the terminals of the capacitor (4).
10. Crossover Capacitor Replacement
10.1 Connect the leads of the capacitor (4) to the wires and solder the connections. The capacitor is wired in series with the woofer’s (1) negative terminal and the Twiddler’s (2) positive terminal. Refer to Figure 1.
10.2 To prevent air leaks, replace the Twiddler panel (15) and gasket (9). Line up the Twiddler panel (15) with the cabinet and replace the four screws (12) that secure it to the baffle.

EXPLODED VIEW 

Wiring Diagram Table

From	To	Wire
Twid 1 (-)	Twid 2 (+)	Gray
Twid 1 (+)	Woofer (-)	Black
Twid 2 (-)	Woofer (+)	Red
Woofer (+)	Terminal 1 (+)	Yellow
Woofer (-)	Terminal 2 (-)	Green

TEST PROCEDURES

1. Woofer Rub and Tick Test
1.1 Apply a 6 Vrms, 10 Hz signal to the speaker input terminal. No extraneous noises such as rubbing, scraping or ticking should be heard.
Note: To distinguish between normal suspension noise and rubs or ticks, slightly displace the cone of the woofer with your fingers. If the noise can be made to go away or get worse, it is a rub or tick and the woofer should be replaced. If the noise stays the same, it is normal suspension noise and the woofer is okay. Suspension noise will not be heard with program material.
2. Air leak Test
2.1 Apply an 8 Vrms, 65 Hz signal to the speaker input terminal.
2.2 Listen for air leaks around the cabinet seams, Twiddler™ panel, and the woofer and Twiddler gaskets. Reposition or replace any gasket that is found to leak. Repairs made to the cabinet seam should not be visible from the exterior of the speaker.
Note: A whooshing noise from the ports at approximately 65 Hz and 185 Hz is acceptable (port tuned frequencies).
3. Twiddler Phase Test
3.1 Check the wiring of the Twiddler.
4. Sweep Test
4.1 Apply an 8 Vrms, 10 Hz signal to the speaker input terminal.
4.2 Sweep the signal generator from 10 Hz to 5 kHz and then back to 10 Hz.
4.3 Apply a 3 Vrms, 5 kHz signal to the speaker input terminal.
4.4 Sweep the signal generator from 5 kHz to 15 kHz and then back to 5 kHz.

4.5 Listen for buzzes, rattles or other noises. Redress any wire that buzzes; replace the woofer or Twiddler if they are found to be defective.
5. Woofer Phase Test
5.1 Observing polarity, momentarily apply 8 VDC to the speaker input terminal.
Note: To avoid damaging the speaker, only momentarily apply the DC voltage.
5.2 The woofer should move outward with the application of the DC voltage.

Schematic Diagram

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