Good manual. Even it is an old printed manual, it is well scanned and complete, with all drawings, schematics and parts list. Very good return for the cost.
Thank you very much, I've been very happy to find this manual on "Owner Manual". It's a perfect copy and it has been really useful for my work!
Text excerpt from page 7 (click to view)
Power Amplifier
Reference 7520a/7521a
TROUBLESHOOTING
� PROBLEM: No audio (POWER LED is off). CAUSE and SOLUTION: No voltage at BATT+ and/or REM terminals, or bad or no ground connection. Check voltages at amplifier terminals with VOM. � PROBLEM: No audio (PROTECT LED flashes every 4 seconds). CAUSE and SOLUTION: DC voltage on amplifier output. Amplifier may need service; see enclosed warranty card for service information. � PROBLEM: No audio (PROTECT LED is on). CAUSE and SOLUTION: Amplifier is overheated. Make sure amplifier cooling is not blocked at mounting location; verify that speaker-system impedance is within specified limits. � PROBLEM: No audio (PROTECT and POWER LEDs flash). CAUSE and SOLUTION: Voltage less than 9V on BATT+ connection. Check vehicle charging system. � PROBLEM: No audio (PROTECT LED is on). CAUSE and SOLUTION: Voltage greater than 16V or less than 8.5V on BATT+ connection. Check vehicle charging system. � PROBLEM: Distorted audio. CAUSE and SOLUTION: Input sensitivity is not set properly, or amplifier or source unit is defective. Check INPUT LEVEL setting, or check speaker wires for shorts or grounds. � PROBLEM: Distorted audio (PROTECT LED flashes). CAUSE and SOLUTION: Short circuit in speaker or wire. Remove speaker leads one at a time to locate shorted speaker or wire, then repair. � PROBLEM: Music lacks �punch. � CAUSE and SOLUTION: Speakers are not connected properly. Check speaker connections for proper polarity.
STATUS LEDs Clip: Indicates the amplifier is being overdriven, and your speakers may be in danger. This should blink only on musical peaks, and not be on constantly. Power: Indicates the amplifier is on. Protection: Refer to �Troubleshooting� for specific indications. Figure 15. LED status.