Low rumbling noise when SX-1050 first powered on

jeffpaletz · May 25, 2014

I have a Pioneer SX-1050 receiver that I purchased new in the late 1970s. It was in daily use until the year 2000 when I got a surround receiver. It has since been used semi regularly in the basement.

For the last few years when ever I turn it on there is a low pitched rumbling noise in the right channel which stops after a couple of seconds. It doesn't matter what input is selected and I've cleaned the various pots and switches with deoxit.

I've been thinking about changing the two main large filter caps but I'm wondering if the experts here think that would help. I've looked at the caps and they look perfect, no leakage or bulging anywhere.

The receiver otherwise works and sound great, just as it always has. Great low bass and clean crisp highs. In fact I've run speaker wire up from the basement so I can listen to my JBL L-300s using the Pioneer. I have a switch that allows me to switch between my upstairs surround receiver and the Pioneer.

Guest105 · May 25, 2014

Do you still hear the protection relay closing a few seconds after powering it on?

petehall347 · May 25, 2014

first try unplugging everything from it except for the speakers ..

jeffpaletz · May 25, 2014

kcbluesman said:
Do you still hear the protection relay closing a few seconds after powering it on?

Yes, if the relay took a couple more seconds to close I don't think I'd hear the noise.

Guest105 · May 25, 2014

I asked because my first suspicion was that the relay was stuck (closed), and that you were hearing caps charging. Sound like that's not the issue. If you are going to do some work on it, I would recap the power board before the filter caps. Much cheaper, more likely to be the problem.

larryderouin · May 25, 2014

Is the sound there BEFORE the Relay closes? Or just After. The way you wrote the 1st post it makes me think the sound is coming on as soon as you flip the switch and before the relay clicks.

Open it up and physically watch the relay while on start up. The contacts may be welded together and you'll still hear some "click" as the solenoid is energized. If the contacts are welded together you'll need to replace the relay and check the protection circuit.

jeffpaletz · May 26, 2014

The rumbling sound comes on only after the relay closes. For example, if tuner is selected, music will come on at the same time the rumbling is occurring. The relay is working fine.

Watthour · May 26, 2014

Cycle the receiver off, and allow about 15 seconds for the caps to discharge (not the main caps, but those in the protection circuit). Turn the volume to minimum, which is arguably always good practice when shutting down and starting. Start the unit and measure the time between power-up and the speaker relay closing.

markthefixer · May 27, 2014

big caps not likely the culprit, the smaller caps on the power supply board are more likely suspects, but ALSO there's the various power filters on the various audio board's power inputs. The fact that it does it in ONE channel points away from main power, try cutting out the tone control, and the filters, then for grins, swap the l/r at the pre-out/power-amp-in jacks in back.

See if the volume control eliminates it as well. Not likely but worth a try, since it's easy...

There ARE 2sa725's in the flat amp, precisely in the point I've described. Between the volume control and the pre-out when the tone and filters are defeated.

They share filtered power in the flat amp, so it has to be the right channel 2sa725, Q8.

jeffpaletz · May 27, 2014

Wow Mark, you are right on. When the tone control is off, there is no rumbling sound at all. It actually does it in both channels with the tone control on ,though not always in the left channel. Thanks for the information. You are the best at this.

markthefixer · May 28, 2014

You changed everything with that post.

Tone control off = no rumbling means it's in the tone control
and the tone control has INDEPENDENT power for each channel,
tone control has 2sc1312's which are less likely to fail.
best advice: recap and re-transistor the tone control.

as long as the filter switches being off or on has no effect upon the rumbling,
you did try them, right?

jeffpaletz · May 28, 2014

I tried it again over the last few hours with filters on or off and it makes no difference. The rumble is only when the tone control switch is on.

markthefixer · May 29, 2014

cap could be loosing capacitance and allowing some "motorboating" or self oscillation with too much low frequency gain.

you can TRY turning the bass all the way down and see what happens, but it may be independent of those settings.

were the actual tone switches cleaned, not the on and out switch, but the actual frequency element settings?

Still stand by recommendation of recap and re-transistor the tone amp.
Caps because they are the most likely suspects, transistors because there are better ones now, they're inexpensive, and you will be IN there changing the parts.

jeffpaletz · May 30, 2014

I'm not sure what you mean by tone switches. Are you referring to the 4 pots that control the bass and treble or something else?

markthefixer · May 30, 2014

jeffpaletz said:
I'm not sure what you mean by tone switches. Are you referring to the 4 pots that control the bass and treble or something else?

Yes, those 4

also
I would really like to see:

you can TRY turning the bass all the way down and see what happens, but it may be independent of those settings.

jeffpaletz · May 30, 2014

With both bass controls completely counter clockwise, it didn't make the noise at all. I am quite surprised. I will wait a while and try it with the bass controls at zero and report back. Normally I have the 50hz control at +5 and the 100 hz control at +2.

markthefixer · May 31, 2014

technical explanation: failing caps lose their capacitance, decrease the balance of feedback, allowing more bass gain, especially as the frequency drops.

Recap (needed), re-transistor ( a good idea, while in there) the assembly.

jeffpaletz · Jul 2, 2015

The problem is getting slightly worse and I'm comfortable working on these boards after changing some caps and resistors in my SX-1980 filter circuit.

There is no rumbling noise when the tone control switch is on and the tone controls are set at zero. The rumbling is there for a couple of seconds when the bass tone controls are at +5 at 50hz and +2 at 100hz which is how I normally use the receiver.

What capacitors do your recommend I change? Can you please provide me with the current parts list for the tone control board so I can order the parts and change them all if I choose to?

qguy · Jul 2, 2015

All the caps on the board needs to be change. As MTF suggested, some problematic transistors needs to be change as well

As for the parts list, Do a search for the name of the board posted by MTF. He normally post a list on a thread where a recap is required.

markthefixer · Jul 3, 2015

jeffpaletz said:
The problem is getting slightly worse and I'm comfortable working on these boards after changing some caps and resistors in my SX-1980 filter circuit.

There is no rumbling noise when the tone control switch is on and the tone controls are set at zero. The rumbling is there for a couple of seconds when the bass tone controls are at +5 at 50hz and +2 at 100hz which is how I normally use the receiver.

What capacitors do your recommend I change? Can you please provide me with the current parts list for the tone control board so I can order the parts and change them all if I choose to?

Marty, Socal's List of lists

SX-1050

this post follows all the links from that first sx-1050, to the latest updated list I was questioned on
This list includes transistors as well. Just 4 for the tone (control) amp.
The variations just reflected the changing of stocked and available parts numbers for the same value components.

And while I would USUALLY criticize the lack of "initiative" in not LOOKING for the SX-1050 recap list first (THEN ASKING if that's the latest list), the path from the "list of lists" thread, to the latest list did get a bit involved, and I would have had to follow it anyways.

Low rumbling noise when SX-1050 first powered on

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