Dsp Pcb Troubleshooting Procedures - Bose Loewe Concertos Acoustimass 61247 Service Manual

DSP PCB Troubleshooting Procedures

DSP PCB Troubleshooting Procedure Setup
1. Remove all test cables used in the amplifier test procedures, if necessary, and reassemble the
electronics module, leaving the top cover off. Refer to the Digital Bass Box service manual, Loewe
part number 90374.921 for disassembly/assembly procedures.
2. Using the test cable, part number 90377.906, connect the module as shown in Figure 45. Test
Setup Diagram shown in the appendix. Using this setup, the amplifiers will not be un-muted, so
you won't be able to pass an audio signal through the module, but the voltages and signals shown
in the DSP troubleshooting section will be present. You will not be connecting a PC or an audio or
digital signal source. You will use the 3.5mm mono jack and a 9 Volt battery to turn the module on
after applying AC mains power through the power cord.
Note: If you disconnect AC mains from the module, you will need to disconnect and reconnect the
9 Volt battery to the 3.5 mm plug to get the module to power up again.
1. Quick Check/Possible Problems With DSP PCB
1.1 Because the DSP IC's legs are very fine, there is a chance for shorts or opens. Probing can
result in shorting them. Boot data can be garbled due to a short or open on the DSP IC pins.
1.2 The 40 MHz oscillator, CR400, might not be working.
1.3 There might be a broken "via" in the PCB. This is a hole in the PCB that connects traces on the
top side of the PCB to traces on the bottom side of the PCB. This type of problem can be difficult
to isolate.
1.4 If the problem has not been isolated, go to procedure 2.
Note: Refer to Figure 8. DSP PCB Test Point Locations Layout Diagram, Solder Side on page 19
for the following procedures.
2. Miscellaneous DSP PCB Troubleshooting Tips
2.1 +17V, ±12V Power Supplies
The PCB draws power from three different supplies:
2.1.1 +17V unregulated, at about 250 mA when everything is running normally. The +17V
supplies the unregulated voltages for the two voltage regulators on this PCB: the
+5V linear regulator U1, and the 3.3V switching regulator U500. The +17V is
brought onto the PCB from J8 pin 3.
Note that the +17V unregulated supply can vary from about +17V to as low as +10V, depending
on conditions. On the bench, the value may be more typically +15V or so. Whatever
the exact voltage, in this document it will be referred to as the "+17V" supply.
2.1.2 ±12V, at about 40 mA or so. The ± 12V supplies are for the op-amps U103 — U105.
+12V is brought onto the PCB from J8 pin 1, and -12V is supplied from J8 pin 5.
2.2 +5V Supply
Check the +5V supply first, since the +5V powers the microcontroller and without it, nothing else
works. Check the following points:
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