NAD-S300-int-si1 维修电路原理图.pdf
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NAD-S300-int-si1 维修电路原理图.pdf
Service Information S300 Circuit Change PROBLEM: You may receive a complaint that the unit goes into protection mode. CAUSE: The transistors in the gain stage maybe overheating causing a dc offset in the output. SOLUTION: Increase the value of resistors R311/313 and R312/314 from 93 ohms1/4w to 180 ohms 1/4w. The dissipation of transistors Q307/311 and Q309/313 drops significantly. Please pay attention to any discolouring of the pc board as it may indicate the transistors need replacing (prolonged heat may cause transistor to drift or breakdown). After performing the above change, check the idle current. A value of 30 -35mV is normal. Excessive idle current can blow the amplifier channel. Also if the idle current cannot be adjusted up enough then change the value of R501/502 on each amplifier board. If these resistors are 4k on the board (the service manual may indicate 1.5K) increase slightly. A 4.7 k gives good results. Please note: A variac is definitely required for setting the idle current. Bring the AC voltage up slowly while monitoring the idle current. Contact: NAD Electronics International 633 Granite Court Pickering, ON Canada L1K 3K1 Voice: 905-831-0799 FAX 905-837-6357 10/6/03 RadioFans.CN 收音机爱 好者资料库
