Nad 522 Service Manual 2

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NAD 522/L40 MODIFICATION Adding Protection circuit after changing the laser mechanism This will prevent further damage by ESD, power surges etc. MODIFICATION: After changing the laser mechanism (partno: 4102-5002-0) please perform the following modification: 1) Change R137 from 10 Ohm to 20 Ohm 1/8 W min. 2) Add a diode 1N4148 between LD and GND on J2 (cable connection to laser unit), Kathode to LD. 3) Cut trace just after collector Q101. 4) Add coil 10uH in between here. The required parts are available from FED in a small kit, partno: 522-LASER-PROT-KIT PRODUCTION: Please note this modification is being implemented in running production. The Nad 524 already has this modification except for: 1) Change R137 PAGE 5-99-01

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NAD 522/524 SERVICE HINT PROBLEM: CD Player does not read disc, skips, produces scratching noise only on some specific CDs CAUSE: The so called playability is affected by the use of low quality discs, scratched discs and CDRs. The problem here is not the true jitter performance of the unit itself but the capability of handling the poor quality discs without audible effects. POSSIBLE SOLUTIONS: 1) Add a ceramic capacitor 100pF at C309 position. 2) Change C122 from 1pF(NAD 522) or 5pF (NAD524) to optimum value between 2.2 and 8 pF. Note that higher value will result in lower jitter with normal CD but practically worse performance on CDRs Best balance is usually 3.3 pF 3) Re-route the cables J5 and J10; make sure they have minimal interaction with J1 and J2. THE FOLLOWING HINTS MUST NOT BE PERFORMED WITHOUT SPECIAL MEASURE EQUIPMENT. 4) Adjust TILT-screw on the laser unit for minimal Jitter with help of a Jitter meter. This is the lower mounted screw at the yellow metal plate in the corner. 5) If the laser power is above 24mW the unit will malfunction after playing for some hours. A Laser power meter is required here. Adjust laser power down to 18-22 mW. PAGE 5-99-02