A vintage Pioneer SX-450 receiver that had a reported loud hum on the output.
This is a receiver from the days of wooden end cheeks and brushed aluminum front panels, something manufacturers don’t do any longer.
After a bit of probing around the circuit board with an oscilloscope I found a failed capacitor in one of the power supplies that was allowing 50Hz from the mains to get onto a power rail. That affected the amplifier that put it out to the speakers as an annoying hum.
In the world of power amplifiers it’s nothing special at only 15W per channel, but it’s well made and looks far better than a lot of modern HiFi.
It doesn’t sound too bad either from its proper transistor output stage.
If need your modern or vintage amplifier repaired please email me with any photos and part numbers at: firstname.lastname@example.org
Interesting wiring in this old Pioneer, all the point to point wiring is done using wire wrap. That’s where you insert long metal posts into the circuit board and by using a tool called a wire wrap gun it tightly wraps a solid piece of wire around the post. No soldering required and no difficult to find or replace connectors.
It’s a pig if you want to remove a load of wires to take a circuit board out though!
Below is a video look at the unit, showing both inside and out that I’ve put on the Orangevalley Systems YouTube channel.
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