Bose 3-2-1GS Series II Service Manual page 92

Bass Module Troubleshooting Tips
Symptom
Any time you remove the
Amplifier / DSP PCB from
the heatsink and re-install
it
No power to the system
No power to console
F1 on the Input/Output
PCB blows
Unusually loud hum from
transformer, mains fuse
may blow (dual voltage
unit in a 230VAC
environment)
Console powers up, unit
plays only at low volume
(dual voltage unit in a
115VAC environment)
Audio crackles/ breaks up
on program peaks at high
volume
No audio, any channel
Audio regularly drops out
at medium to high volume
(may affect bass, left array
or right array
independently)
Check for...
- Clean off all remnants of the old thermal pad (on heatsink,
rectifiers, and FET) and replace thermal pad (267968-075) on
heatsink.
- Be sure thermal compound (144087) for amplifiers (U150, U250,
U350) is clean and properly applied.
- Install cable connectors in J5 & J7100 before screwing down the
amplifier/DSP board & mounting bracket (267183-001).
- Be sure all cables are properly installed.
- Check transformer primary & secondary connectors.
- Check line fuse on I/O board; replace if necessary.
- Check power switch or dual voltage switch (if present).
- Check resistance of transformer primary. If open, thermal fuse has
opened; replace the transformer.
- Check seating of cable 271561-190 between DSP & I/O board.
- Check F1 on Input/Output PCB.
- Check console cable (269997-001).
- If F1 blows when the console is not attached, check integrity of
console cable, look for damage causing shorts.
- If F1 blows when the console is plugged in, check the console for
shorts.
- Check that voltage select switch is set properly.
- Check that voltage select switch is set properly.
- Check all cables/connectors in ground path to the console (J150
on DSP; 271561-190; J3 & J7 on I/O). Contacts may be corroded;
replace as necessary.
- Check PCB soldering to J150 on DSP. Re-solder if necessary.
- Check Vraw. If it is above 18 VDC (probably 25~30V), replace Q4
FET (274550-002).
- Check seating of amplifiers (U150, U250, U350) for proper thermal
coupling to heatsink.
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