BOSE 194101-B1 Schematic

Bose® Service Repair Information

Service Home Page
Owners Guides

R

EPAIR INFORMATION

Lifestyle

®

Systems

Acoustic Wave

®

Music System

Bose

®

Wave® Radio

321

®

Home Entertainment Systems

Lifestyle

®

Music Centers

Powered Bass Modules
Powered Speakers
Acoustimass

®

Speakers

SoundDock
"01" Speakers
Environmental Speakers
"001" Speakers
"Point" 2 Speakers

RoomMate

®

Speaker

Car Stereo
Headphones
Multimedia
Miscellaneous Products

Built-INvisible

®

Product

Pro Products

Engineer:

Mike
Costa

Technical
Writer:

Robert
Smith

FRACAS
Number:

172

Product:

AmPlus

TM

50 and 100 amplifiers

Bose Part Number: 194101-B1
Subject: Volume ramp-up
Effective Date: 6/98

Serial Numbers: Affected Units

Symptom:

Volume ramps up to full when the amplifier is powered down.

Cause:

The volume control voltage on the voltage controlled amplifiers discharges
before they have powered down in the circuit.

Solution:

Install a 22uF, 50V electrolytic cap and a 1N4148 diode in the locations
shown in the figures, and replace R200 and R220 with 15.8k Ohm resistors.

Details: Note: This modification is only required for AmPlus 50 and 100 amplifiers that are

exhibiting the symptom shown above. In many installations this modification
will not be necessary.

Note: Refer to the AmPlus 50 and 100 Business Music Amplifier service manual,

part number

194101, for the following procedures.

Note: If you are modifying an AmPlus 50 amplifier, you need only perform the

operations that apply to channel 1.

1. Remove the AmPlus amplifier top cover using procedure 1.

2. Remove the Main PCB assembly from the chassis using procedure 3.

3. Using a multimeter, locate the tracks that run from S5, across the Main

PCB, to the via holes shown in

Figure 1. These via holes correspond to M32

and M33 as shown on Sheet 1 of the service manual schematic diagram,
and as silkscreened on the bottom of the Main PCB near S5.

http://serviceops.bose.com/index.htm (1 of 4)6/26/2010 12:22:25 AM

Bose® Service Repair Information

4. Remove the solder in the via holes shown, so that you can install the cap
leads through them.

5.

Using an Exacto

TM

knife, cut the trace on the bottom of the PCB that runs

between the via hole to M33 and the main portion of the trace

(see Figure

2). Be sure to leave the portion of the trace that runs to R200 intact. Verify

that the trace is open using the multimeter.

6. Cut the trace that runs from the via hole to M32 and the collector of Q221

(see Figure 2). Be sure to leave the portion of the trace that runs to R220

intact. Verify that the trace is open using the meter.

7. Install the 22uF, 50V caps (Bose P/N: 137126-220) into the locations
shown. Be sure that the negative lead is installed into the via hole for M32
or M33 as applicable.

8. Pre-form the 1N4148 diode (Bose P/N: 121501) leads as shown in Figure 2,
and solder them in place as shown.

9. Replace R200 and R220 with 15.8k Ohm resistors (Bose P/N: 133625-

1582). This is to keep the loading on the circuitry the same as before
modification.

10. Replace the Main PCB assembly into the amplifier chassis using procedure

4.

11. Replace the AmPlus amplifier top cover using procedure 2.

http://serviceops.bose.com/index.htm (2 of 4)6/26/2010 12:22:25 AM