Service Bulletin Inf9902 Rev 1 - February 2001 - Infinity BU-120 Service Manual

Service Bulletin INF9902 Rev1 - February 2001
To: All Infinity Service Centers
Models: BU-80, BU-120, BU150, HTS-10, HTS-20
Subject: Check Solder Joints in Event of Failure
Some performance related complaints in the BU Series powered Subwoofers may be caused by cold solder
connections between the 28 pins of the Power Amp Module and the main circuit board. When troubleshooting,
failure to check these joints can result in erroneous conclusions or wasted time.
In the event you receive a Subwoofer with the complaints "Dead, or No Output, or Motorboating
(Oscillation)", perform the steps listed below first before any further troubleshooting takes place:
1) Unplug all cables, lay the subwoofer on a padded surface.
2) Remove all Philips screws around the outer perimeter of the amplifier faceplate.
3) Remove amplifier assembly; you should be able to remove the amplifier far enough out of the cabinet to
service it without removing the woofer wires.
4) Locate the Power Amp Module; it is the large gray component with a metal case. On the solder side of the
circuit board are the 28 soldered connections to the Module.
5) Regardless of whether you can visibly see breaks in any of the connections or not, carefully re-solder all 28
pin connections, adding 60/40 rosin core solder. Take care not "bridge" any connections on the board with
solder.
6) Inspect the solder joints to the main filter capacitors C1 and C2 on the main PCB and re-solder if needed.
7) Replace the amplifier assembly back into the cabinet; replace the screws.
8) Test the unit by applying a signal from a music source, adjust the volume to a moderate level and confirm
the original problem has been corrected.
IMPORTANT SERVICE NOTES: When testing the BU or HTS Series amplifier, a load must always be
connected to the output terminals, whether the woofer, or a 4 to 8 ohm resistive load.
All AC powered test instruments (meters, oscilloscopes, etc.) must have a floating ground, i.e. be connected to
an isolation transformer.
Infinity Systems, Inc. 250 Crossways Park Dr. Woodbury, New York 11797 (516) 496-3400
Service Bulletin
This is considered a Minor repair
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