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Sony TA-F35 Left channel dead. Fuse blown. O/P transistors 2SA771 and 2SC1986 found s/c. Replaced with TIP41C and TIP42C. Surrounding components checked. Resistors R313 and R415 (both flameproof) had gone very high. Also Q304 (2SD667) found to be B/E open and leaky C/B. All above replaced, bias voltages adjusted. Unit OK.
Sugden A48 Unit blows Rt. Ch. Fuse. Power transistor 2N3055 found s/c. Also driver transistor BD520 s/c. 2N3055 replaced. BD520 unobtainable so substituted BD180. Adjust bias voltage. Unit OK.
JVC JA-S11G Lt. Ch. operating but with protection relay cutting in and out. Very loud crackling noise. No DC offset found at O/P but STK power I/C input voltages fluctuating. Driver transistor X607 (2SB560) tested with freezer spray. Noise much worse. X607 replaced with 2SA965. Unit OK.
Pioneer A-33 Bass control has no effect. Replaced dual op. Amp. M5210 with M5220. Unit OK.
Marantz PM-310 Very loud hum in both channels. Power supply filter / reservoir capacitors replaced. Unit OK.
Sansui AU-9500 Huge ‘flagship’ amplifier weighing 25kg! Very loud crackling noise in right channel. This noise was apparent with the volume control turned down, so at first the right channel driver block was suspected. On this amplifier the pre and power amps are separable via links on the rear panel, so the right channel link was pulled and the unit powered up. Noise now gone so power amp OK. Checking back into the tone control block with an external amp, transistor TR712 (2SC1313) found to be noisy. This transistor replaced after checking surrounding components. Unit OK. Interestingly, the same transistor in the left channel had also been replaced at some time in the past. A generic fault perhaps?
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