Al pha 1200s
Service Bulletin
Service Bulletin INF2004-01 - March 2004 This is considered a Minor repair
To: All Infinity Service Centers
Model: Alpha 1200s
Subject: Distortion When Coming Out Of Standby
In the event you receive an Alpha 1200s 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, Infinity Part# ZMM5227BCT-ND.
When replacing D60 the polarity of the new (zener) diode should be reversed.
5) Add new 27K& resistor, Infinity Part# 299-27K, to the indicated connections. (This component,
electrically, will be in parallel with R37, reducing its value to <22K& ). 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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ACEC
