We have a little Pioneer SX-550 Receiver in today, thought we'd show some highlights. Produced for a limited run from 1977 to 77" its features a 3 gang tuning capacitor and modest 20W rated output. The 550 was the entry class for many SX users because of its price point.
Switch/Repair & Modification
One of the common issues with the lower series SX Pioneer's is the integrated Power/Speaker Selector switch. Both sections of the phenolic based speaker switch and integrated power switch are prone to excessive carbon build up and then AC arching. often presenting as fluctuating AC/ flicker lamps. If you place you ear near (*caution...) you can actually hear the arching.
One fix is to tear down the switch and phenolic assembly by desolder and removing the unit. As photo'd below its important to scour and clean the contact points and clean and treat with a high quality non residue cleaner.
In some cases, such as this.... no matter how much cleaning occurs the switch is done for. In that case I recommend salvaging and cleaning the speaker selector and we did and adding a new power switch to the rear of the chassis for discrete mounting. A 5A DPDT single throw was chosen for this unit with a Vishay X1Y2 safety capacitor installed parallel the switch.
New multi-facet LED's were installed along with a LED function indicators. to give off a new clean/ white glow!
The resulting verification report was as expected with a slight deviation in the low frequency to sub-sonic frequency response at 10Hz to 35Hz with a noted deviation of +1dB.