Trio KA-1500 Mk 1 Unit completely dead. Power supply fuse found o/c. Also incorrect value - should be T1.6A: was 650mA. Fuse replaced, unit powered up. -30V found at left channel O/P. Left channel power transistor 2SD525 s/c emitter/collector. 2SD525 & 2SB595 replaced with TIP41 & TIP42. Checking surrounding components found o/c 0.47R resistor R73. Also R69 330R observed to be burnt.
While checking out left channel power supply fuse blew again! This time right channel 2SC1509 found leaking emitter/collector. Also 2SD525 found emitter/collector s/c. R74 0.47R found slightly burnt. All above replaced. Bias voltages adjusted. Unit tested OK.

Trio KA-1500 Mk II Left channel distortion. Original O/P pair found replaced with TIP41 / TIP42. TIP41 found to have low base/emitter voltage (0.47V). Also capacitors C41 & C42 (10mF 25V) found burned. All resistor values checked - OK. TIP41/TIP42, C41, C42 replaced. Unit tested OK.

Hitachi HA-12 No O/P both channels. Both centre pins on stereo power amp I/C STK 4141II found blown off board! I/C replaced. Surrounding components checked. Unit tested OK.

Marantz PM80 Owner reported “loud noises” from Rt Ch. -59V found on Rt. Ch. speaker terminals. O/P transistors and all other discrete components in power amp check out OK. Voltages taken on pins of Q721 - an STK3102IV. All readings left and right comparable except for the two outer pins on each side. Left: 1=0V, 2=0V Right 1=0.2V, 2=-9.3V.
Rechecked outer pins on right channel. Found they were now 0V & 0V! Re check speaker terminals- 0V DC.
Amp tested quickly. Both channels OK. As Q721 common to both channels this I/C suspected as intermittent ( owner had mentioned that the left channel would sometimes cut out ). STK3102IV replaced. O/P test: Rt Ch 6.5 mV offset. Lt Ch 7.0mV offset. Unit OK.

Pioneer SA-608 Fluctuating DC offset (1-3 volts) found on Rt. Ch. O/P. O/P transistors, drivers and pre-drivers all tested - OK. Very small voltage fluctuations (a few mV) noted on dual transistors 2SC2291 and 2SA798 although both devices diode tested OK. Devices replaced. Unit OK.

Pioneer SA-510 No display function. Voltage regulator transistor 2SD880 found loose on board (all solders failed). Resolder - unit OK.