Small world that it is I ended up with two Pioneer SX-434 vintage receivers for repair at the same time.
One illuminated the tuning dial and signal strength meter but in all other respects was dead due to a couple of blown internal fuses.
After the fuses were replaced the Pioneer burst into life except one speaker channel kept producing some nasty pops and cracks when first switched on. This was a bit dramatic and could be why the fuses blew.
It wasn’t the more common crackle noises you can get when turning the rotary controls such as the volume control.
The other Pioneer SX-434 sometimes wouldn’t switch on. On looking in the mains plug I found it had been correctly wired but none of the screw terminals had been tightened!
It was also putting pops and crackles onto both speaker channels like the other Pioneer SX-434 was.
Looking at the speaker output terminals with an oscilloscope showed lots of dramatic voltage swings to the power rails along with strings of pulses as if an output transistor was rapidly switching on and off.
So, the reason for the loud pops and crackles? Component failures, which given the age of the receivers is hardly surprising.
These are great 15w per channel receivers that are very well built. They’re not the most powerful amplifiers but they provide enough power for most people.
From a repair aspect the component side of the amplifier circuit board is almost impossible to get to and there aren’t any component IDs printed on the boards making repairing them more complicated than it could be.
If you’ve got a vintage Pioneer SX-434 or any other vintage amplifier or receiver you need repaired please contact me for a repair quote. I’m based near Stroud in Gloucestershire. Items can be shipped to me from anywhere in the UK or dropped off by prior arrangement.
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