I'm concerned about my Pioneer SX

[Pedrisco]

Hi everyone,

Today I bought a pair of some old and cheap Whaferdale Denton speakers. They were in nice shape and they were sold me as working alright.

When I got home I hooked them up to my flawless Pioneer SX-535, I turned it on, and the speakers started to produce loud crackling, static and (I believe) popping noises, even with the volume all way down. I turned the receiver off after a few seconds, fearing some damage to the receiver.

I disconnected the Whaferdales and connected my usual Castle speakers, and with great concern I realized that the noise was still present. I feared the worse, that the 535 was fried. I don't now how, but gradually, in about 10-15 minutes, the noises started to diminish, and now it seems the receiver is working again normally.

I measured the impedance of the Wharfedales, and they read about 6 Ohm, one, and the other about 10. So, they are not shorted. I measured also the tweeters (connected to the crossover), and they read about 0.8-1 Ohm.

My question is: what happened here? Even though the 535 seems now to be working fine, may I have damaged it in some way?

Thanks!

Pedro

 

[elnaldo]

Sounds like small signal transistors starting to fail. I'd check if your amp uses the 2SA798.

One speaker reading 6ohm and the other reading 10 doesn't look OK. What you measure is DC resistance, not impedance.

 

[ivandezande]

The above. It has 2SC1318's and 2SA720's in the power amp section which go bad. Replace with KSC2383Y/KSC2690AY and KSA1013. 2SC1344 in the EQ amp, replace with KSC1845.

Did you measure your speakers while connected? Because that does not sound right at all...

 

[Fred Longworth]

As elnaldo notes, there should not be a 4-ohm discrepancy between the two speakers. An 8-ohm IMPEDANCE speaker will measure about 6 ohms on a digital multimeter, like a Tenma or Fluke, which only measures the resistive component of the 8-ohm impedance. So . . . actually I'm wondering about the 10-ohm measurement. You might have oxidized contacts, say, for example, at the terminals on the back of the speaker enclosure.

As for the SX-535, the common failure causing noise with the volume at a minimum is the differential amplifier transistor pair on the power amp board (two per channel). These get leaky. Also, if the set has lived near the Atlantic, you may also get conductive saline deposits on the surfaces of the smaller (e.g. TO-92) transistors in the power amp section. Often you can scrape these deposits away with a dental pick. Be sure to discharge your power supply caps with, say, a 10-ohm 10 watt resistor and two clip leads, before touching any parts.

Although the following doesn't pertain to your complaint, replace the blue Sanyo capacitors on the preamp board mounted to the front panel. These die!

Good luck with this.

Fred

 

[Pedrisco]

Thank you all for pointing me out those transistors. As you already sensed, I'm no electronics expert by any means -- thanks elnaldo for the DC resistance note --, however I still don't get what happened here. The Pioneer was working perfectly before, it's working again perfectly now. Can a pair of somehow offending speakers trigger (1) a malfunction on those parts, (2) a malfunction that is temporary?

 

[ryuuoh]

Trying the speakers on another amp might be useful.

 

[ivandezande]

Thank you all for pointing me out those transistors. As you already sensed, I'm no electronics expert by any means -- thanks elnaldo for the DC resistance note --, however I still don't get what happened here. The Pioneer was working perfectly before, it's working again perfectly now. Can a pair of somehow offending speakers trigger (1) a malfunction on those parts, (2) a malfunction that is temporary?

I would assume if there's something not quite wired right with those speakers, it could affect the amp circuit as it sees the load indirectly, current and such possibly. Someone else will know better. It's not gonna be temporary though I can tell you that. It needs to be serviced just based on the Sanyo caps that become resistors and the bad transistors.

I wouldn't put those speakers on another amp until look make sure they're wired ok.

 

[Silentnet]

I think it was pure coincidence in this case, nothing to do with the speakers.

 

[Pedrisco]

I think it was pure coincidence in this case, nothing to do with the speakers.

You're right -- speakers have been tested with another amp with no issues

What I don't get is how the problem went away by itself

 

[Watthour]

One possibility is that some of the components in the output section are on the borderline of failure. The potentially lower impedance of the speakers you connected could have pushed it beyond its limit.

In other words, it probably is not fixed, but just waiting a little longer before it exhibits the behavior with any load connected.

 

[slimecity]

If the speakers sound OK on another amp - theres no issue with them.

Because of how they were designed - Pioneers in general had some specific issues that come up across models - of the issues I am aware of: one is the input pair failing, the other is power supplies not being properly rated for the loads they are delivering. You are getting the first issue.

Its only a matter of time before the issue shows itself - the problem is a transistor one and transistors change their characteristics between temperature - faulty/dying components will usually show themselves in a cold or a hot state. When its really bad, the issue is there all the time.

The answer is most likely in elnaldos post #2 above.