Hi Everybody ,

My Pioneer receiver has some issue on switching, when i switch on, in three seconds it clicks off and again clicks on and again clicks off never remains open, some says that safety filters has some problem, some friends says the output transistors has an issue

can anybody knows what cause this

thank you in advance
Eli

I'll guess poor/cold solder joints within the power supply section. Pop the covers off and have a look around where the caps and voltage regulators are soldered to the PCB. You'll immediately know if you're having these types of probs as the cold joints are unmistakable, and plentiful.

It could be the speaker protection circuit sensing DC voltage on one or both of the output connections. There are often adjustments for this to compensate for aging components in the power amplifier sections.

Dave

I think it is a protection circuit gone wrong. I have a couple of sets destined for the prizes after having blown out a couple of voice coils of innocent speakers. Use power resistors and ammeters to debug, not speakers.

Cap-changing time.
Anthing else is a waste of effort.

If it isn't the caps, you might have burned out the output transistors. Still recommend you use non inductive resistors to debug. Of course replace the caps then go further.

Pioneer power regulator boards are under-sized and over worked. As everyone else has said, do a careful visual check for e-caps with melted or shrunk wrappers. Use a magnifying glass to check for burn spots or over heating on PCBs. The OP transistors shouldn't be too hard to pull and test. A pioneer SX-1250 I fixed had numerous e-cap problems, even 2 of the 4 main power caps had melted wrappers.

I've got several 1250's in the shop right now.
They all need a complete re-capping from top to bottom. - not just a handful of caps either.
The 1010's do as well.
40 years is enough for those old caps, time to hit the bricks.

Expect to invest heavily in caps and labor.

Unauthorized triggering of protection circuits on Pioneers like yours tends to be due to--

(1) Intermittent malfunction on power supply board.
(2) Intermittent malfunction of the protection circuit itself -- usually a capacitor in the timing circuit.
(3) Failure of the audio power amp circuits -- but not the outputs. Look at the differential amplifier transistors. These get leaky or the beta (HFE) corrupts.
(4) If you live near the Pacific or Atlantic, look for saline deposits on the underside of TO-92 transistors in the power amp or protection circuits. The saline deposits conduct, and cause the transistor(s) in question to malfunction. These deposits can be removed with a dental pick or Xacto knife.

As has been mentioned before in this thread, Pioneer is "famous" for underdesigned power supply boards. On the big brother of the SX-980, the SX-1980, you have to replace every cap on the power supply board and most of the transistors. If you skimp on this, the set will come back.

I'm not big on full recapping, though. It turns out that heat and current (which causes heat) are the culprits as far as killing electrolytics. Some parts of the set won't need recapping for another decade or two. Also . . . few customers will pay for a full recapping. Most of the full recap jobs that I see at my shop were actually performed by a part-time community college student, or similar -- and the quality of workmanship is shoddy and horrible. That's the only way the shop can keep the price low enough so that a customer will go for it. Also, the chief tech will refuse to do a full recap because, frankly, it's boring.

When replacing the caps on the power supply board, use 105-degree devices. Panasonic and Nichicon make excellent-quality replacements. Try Digi-Key and Mouser.

Fred
owner
Classic Audio Repair

Fred. thanks for the info, however I'm currently doing (in stages) a Full Recap of a 1250, and have another 1250 waiting in the wings.

Yes, it IS a boring, tedious job.
And yes, the customer is willing to pay.

Some people just appreciate the value of good audio, and good work.