hifi engine

Pioneer SX-1280 Receiver

Hello to all!
I'm currently listening to a Pioneer SX-1280, and thinking about buying it.
It has a problem with the protection circuit activating itsel at any point in time.
Whether at low or moderately high volume, the circuit engages and turns off the speakers.
It may do it, at times, with the volume at min and no input.
Has anyone had this sort of experience with this Pioneer series?
There are a few models from this era that shared the same protection circuit.

Any help would be appreciated.


Re: Pioneer SX-1280 Receiver

I have a SX-1280, and the units was doing the same thing when I received it. I found a noisy transistor on the driver board. it was a 2sc869 small signal transistor. I replaced it with an equivelant type (probably a 2SC2240)
I am not sure if the problem showed up as intermittent DC on the outputs, but I do remember that one of the pins (I believe pin 8) did show fluctuating voltage, which cause the protect to engage from time to time. The problem also happened t any volume level.
But unless you are familiar with working on units such as this, you should bring it to a "Vintage electronics Specialist". This units uses very rare output transistors, which are almost impossible to find, and when you do they can cost up to $220 a pair. And each side uses 2 pairs.

The good news is that the outputs are probably OK in that the units does work from time to time. But if some accidently shorts the wrong connections trying to repair it, can easily result in having to get 2 pairs of outputs paying up to $440.

Re: Pioneer SX-1280 Receiver

Could be something as simple as a bias adjustment. I recommend NOT using the receiver until it is repaired, or damage can result to the amplifier circuits.