Author: Provo Electronics

Parts and repair service for audio /studio HI-FI equipment. Mcintosh,Sansui, Kenwood, Fisher,Pioneer, Marantz, others HI-FI gears. Repair service for vintage audio gears. Audio HI-FI equipment repair and restoration service. Arcade games repair. Metal detector Minelab, Whites, Garrett repair , service. Seattle area.
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Case 567532. 03/01/2023 . Pioneer QX-9900 receiver . Right channel distorted like thunderstorm noise .

After troubleshooting using ” freeze spray ” for transistors method found 2 transistors 2SA726 in right channel driver board acting bad after cold application . All unit transistors 2SA726 changed to 2SA992 . They have same look but different pinout. Pay attention ! 2SA992 / KSA992 is better in parameters and performance.

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Case 456723. 02/26/2023 Marantz 1060 amplifier. No sound on left channel.

After troubleshooting found missing voltage on collector H702 transistor ( 4-5 volt) in driver section.
Problem solved by replacing R708 resistor 18k.
This time we did ” lazy” replacement . New 2 resistors 10k + 8k installed right on top of bad resistor. For saving time.
Technical review.
Nice small amplifier. Good performance. Nothing special.Power supply section extremely simplified. Classical old style engineering design.

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Case 756577. GAS THALIA Servo Loop Preamplifier. Unit has damaged “OUTPUT” plug.

Problem solved by OUTPUT PLUG REPLACEMENT.
Technical design review.
Pluses- simplicity, build simple as possible. Minimum wires used in design . Servo loop channel method ( input signal controlled by output signal) realized in schematic. This method has own advantages and minuses. Some called it “over kill” and unnecessary, some – perfect and high performance support method. Elimination input electrolytic capacitor in signal path is questionable. Debates in process already for over 30 years. Still unique .
Low power unit use for functioning. Good detailed attention to phono input section.


Minuses- no ventilation holes, using no soldering contacts on major transistors ( oxidation )
Power supply filter capacitors installed close to heat emitting heat sink ( heat destroy electrolytic ), not shielded balance pot wires.