Pioneer SX-780

Over the last 40 years, I have probably worked on more than 20 of these units and the variability in assembly never fails to amaze me. In particular is the wiring. 

I can tell right away the level of experience of the assembler simply by looking at the routing of the wiring. It shows how the engineers had the best of intent but it didn’t always transpose to the assembly line. It is evident to an engineer that the designers purposely employed multiple pathways for wiring to keep signal wires and power separated however, where the rubber hit the road, no attention was often paid to this by the assembler and I often find the signal and power leads just randomly routed together…low hanging fruit that is missed here but correctable. 

I never see anyone paying attention to this on rebuilds…even an easy thing a person of limited electronics ability can do to insure optimum performance for the design!

One of the simplest ‘modifications’ I always perform on these is proper wire routing. 

All signal wires have been separated from power wires and routed independently as per the Engineers design and to take it a step further, we segregate the phono input from everything else to optimize signal to noise ratio and quieting. 

All other signal wires have been segregated and run along ground planes and configured to cross at right angles where it is necessary to limit crosstalk…and don’t get me started on components being bent over randomly on boards…won’t find that here!

All electrolytic capacitors in the Amp and Pre-Amp section have been replaced with the highest quality capacitors for the particular circuit involved including Nichicon Fine Gold series, UKA and extreme high quality Polypropylene Stacked Film capacitors!

In most ‘recaps’ you see, the main power capacitors are rarely replaced!...Why is that?...tech’s say “They tested fine so I didn’t replace”. I could go into a lot of dissertation on this but suffice it to say, they are the most expensive components in the receiver, other than the main drivers… AND, testing large value caps isn’t very effective with most capacitance testers due to the limitations of the frequency of the testing. 

Only when testing these caps over the broadness of the audio spectrum do you reveal the whole picture of how that device is behaving at say 30hz vs 1khz. Long story short, we always upgrade these caps, even though it’s expensive because our intent is to have the piece still be working in 50 years and we feel the expense is worth it for the amount of overall labor in the restoration.

The Main Power Supply capacitance was upgraded from 8000uF to 10,000uF. This ‘stiffens up’ the supply a bit more especially at the low frequency spectrum. In addition, we have incorporated precision 2.5uF Polypropylene Stacked Film capacitors in parallel to add some refinement to the filtering at higher frequency.

The Phono Pre-Amp has been modified with the addition of Polypropylene Stacked Film capacitors for the complete audio path from the phono cartridge to the Flat Amplifier.

All controls have been refreshed as necessary. 

The output relay was refurbished via proprietary non-abrasive method and each contact inspected for polished surface. 

Resistance verified in situ after replacement.