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Service Bulletin
Service Bulletin JBL2003-06 - April 2003 This is considered a Minor repair
To: All JBL Service Centers
Model: S120PII
Subject: Distortion When Coming Out Of Standby
In the event you receive an S120PII subwoofer with the complaint “There is a brief chirping sound, or
short oscillation that occurs when the unit is in the AUTO mode, in Standby, when it’s triggered ON
with a music signal”, follow the procedure below to correct this condition:
Synopsis: Replace D60 (RLS4148 diode) with a 3.6V Zener Diode; add new Resistor.
1) Remove the amplifier assembly from the subwoofer cabinet (12 Phillips screws).
2) Remove the Plastic Amp Cover from the faceplate (4 Phillips screws).
3) The area of concern is on the Class D Driver PCB (Small Upright PCB on the MAIN AMP PCB). A
long, thin, soldering iron tip is recommended. Care must be taken not to damage surrounding
components, like large inductor pair L8.
4) Locate, remove D60 (RLS4148 diode); replace with a 3.6V zener diode, JBL Part# ZMM5227BCT-ND.
When replacing D60 the polarity of the new (zener) diode should be reversed
.
5) Add new 27KΩ resistor, JBL Part# 299-27K, to the indicated connections. (This component,
electrically, will be in parallel with R37, reducing its value to <22KΩ). Assure the leads do not come
into contact with any other connections; insulate the leads if necessary.
6) Replace amp cover and return amplifer assembly to cabinet.
7) Test the subwoofer to assure the distortion is no longer present.
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