Leestereo
Super Member
Here are some pictures and details of a Pioneer SX-750 restoration/upgrade project.
Power Supply and Protection Assembly (AWR-099)
This particular example exhibited a constant loud "hum" noise due to the failure of the filtering capacitors (C17, C18) in the regulated power supply (AWR-099); this is a relatively common problem for this model.
The original capacitors for C17 and C18 were rated at 330µF/50V and these were replaced with 470µF/63V low ESR types. Note that it is recommended that the voltage rating for these capacitors be increased from 50V (today's higher AC mains voltage results in these capacitors being subject to >50VDC). Capacitors C10, C15 and C16 were originally rated at 100µF/50V and were replaced with 220µF/50V low ESR types. The capacitors C12, C13 (zener shunts) were originally rated at 220µF/16V and 100µF/50V (respectively) and were replaced with low ESR types rated at 220µF/35V and 100/63V (respectively). The capacitor C11 was originally rated at 4.7µF/35V and was replaced with a 4.7µF/50V low ESR type. The final capacitors in the regulated PS (C7, C8 and C9) were were originally rated at 220µF/16V, 100µF/35V and 100µF/50V (respectively) and were replaced with low ESR types rated at 220µF/35V, 100µF/50V and 100µF/63V (respectively).
The original capacitors C1 and C2 (infamous failure-prone Sanyo solid aluminum type) in the Protection circuit were originally rated at 0.22µF/10V and were replaced with 0.22µF stacked film types. The C3, C4 capacitor pair was originally rated at 330µF/6V and were replaced with 330µF/25V low ESR types. Capacitors C5 and C6 in the relay timing circuit were originally rated at 3.3µF/10V and 220µF/16V and were replaced with low ESR types rated at 3.3µF/50V and 220µF/35V (respectively). The original DEC MS4U relay was replaced with an Omron MY4-02 24V relay. Also a small heatsink was installed on Q12 (2SB507); it runs considerably cooler now.
Power Supply and Protection Assembly (AWR-099)
This particular example exhibited a constant loud "hum" noise due to the failure of the filtering capacitors (C17, C18) in the regulated power supply (AWR-099); this is a relatively common problem for this model.
The original capacitors for C17 and C18 were rated at 330µF/50V and these were replaced with 470µF/63V low ESR types. Note that it is recommended that the voltage rating for these capacitors be increased from 50V (today's higher AC mains voltage results in these capacitors being subject to >50VDC). Capacitors C10, C15 and C16 were originally rated at 100µF/50V and were replaced with 220µF/50V low ESR types. The capacitors C12, C13 (zener shunts) were originally rated at 220µF/16V and 100µF/50V (respectively) and were replaced with low ESR types rated at 220µF/35V and 100/63V (respectively). The capacitor C11 was originally rated at 4.7µF/35V and was replaced with a 4.7µF/50V low ESR type. The final capacitors in the regulated PS (C7, C8 and C9) were were originally rated at 220µF/16V, 100µF/35V and 100µF/50V (respectively) and were replaced with low ESR types rated at 220µF/35V, 100µF/50V and 100µF/63V (respectively).
The original capacitors C1 and C2 (infamous failure-prone Sanyo solid aluminum type) in the Protection circuit were originally rated at 0.22µF/10V and were replaced with 0.22µF stacked film types. The C3, C4 capacitor pair was originally rated at 330µF/6V and were replaced with 330µF/25V low ESR types. Capacitors C5 and C6 in the relay timing circuit were originally rated at 3.3µF/10V and 220µF/16V and were replaced with low ESR types rated at 3.3µF/50V and 220µF/35V (respectively). The original DEC MS4U relay was replaced with an Omron MY4-02 24V relay. Also a small heatsink was installed on Q12 (2SB507); it runs considerably cooler now.