Yamaha Portasound PSS-140 keyboard - Noise sound on stand by

[2X]

Hello, I have a Yamaha Portasound "PSS-140" keyboard and when I turn of the switch the speaker make a noise without I have press any button... When I play music the noise seems to disappear but when it is on stand by I hear from the speaker always the same noise. Do you know if the speaker have a problem (if yes how can I check it?) or I have to check something else?

[eleguy]

To me it sounds like the "noise" persists while playing the note as well. Have you tried to move the volume knob back and forth fast/heavily (no need to play note) for a while? It could be that the potentiometer is just missing some exercise...

[Audiorepair]

Knowing whether the volume control controls the noise would narrow things down somewhat.

[YurkshireLad]

Interesting; I have a really old Yamaha PSR something or other that might have the same symptoms. I keep meaning to open it up and investigate, but I haven't gotten round to it yet.

[2X]

Hello,
I changed almost all the capacitors (in the yellow circle), but the noise still exsists. I measured the output with an oscilloscope and I saw a triangle signal. What do you think that is the faulty component (maybe a transistor?)? Is it possible that the speaker has "degrade" over the time and the speaker itself create the noise?

[eleguy]

Hmm, 50kHz is so high frequency that you should not be hearing it. Amplitude is certainly big but maybe it is some sort of PLL "left-over" that got through the low pass. I did listen your sample again and to me it does not sound periodic at all. It sounds like a super noisy resistor.

This can be helpful in your journey

https://elektrotanya.com/yamaha_pss-140_sm.pdf/download.html

[2X]

Hmm, 50kHz is so high frequency that you should not be hearing it. Amplitude is certainly big but maybe it is some sort of PLL "left-over" that got through the low pass. I did listen your sample again and to me it does not sound periodic at all. It sounds like a super noisy resistor.

This can be helpful in your journey

https://elektrotanya.com/yamaha_pss-140_sm.pdf/download.html

Thanks for the reply. Could you tell in what components (like IC2 - PLL2) I have to concentrate my searching. Also, what do you mean by "PLL "left-over"".

[eleguy]

That 50kHz triangle wave is from somewhere (oscillation or from the pll) but I think that is not the "problem" you are hearing. You could measure with your o-scope from the output towards the OPLL2 chip and check from where this triangle wave comes from?

[fenugrec]

You could try disconnecting the signal path somewhere just before the power amp - e.g. that 1uF/50V cap, or the 1K resistor, whatever is convenient. If it's still noisy, suspect IC3 or the supplies (less likely, the rails would have to be horrendously noisy to feed through the IC3). If no more noise, reconnect that 1uF and check earlier - maybe remove the two 10K between the OPL and IC4.

I was going to suggest to rule out the speakers and try with headphones, but that is a very large signal on the output and you risk causing damage. That 2V 50kHz tone has no business on the output...

[2X]

You could try disconnecting the signal path somewhere just before the power camp - e.g. that 1uF/50V cap, or the 1K resistor, whatever is convenient. If it's still noisy, suspect IC3 or the supplies (less likely, the rails would have to be horrendously noisy to feed through the IC3). If no more noise, reconnect that 1uF and check earlier - maybe remove the two 10K between the OPL and IC4.

I was going to suggest to rule out the speakers and try with headphones, but that is a very large signal on the output and you risk causing damage. That 2V 50kHz tone has no business on the output...

Hello, I replaced the IC3 (AN7140) with a brand new but the same thing again. I will try to test the IC4.

[2X]

That 50kHz triangle wave is from somewhere (oscillation or from the pll) but I think that is not the "problem" you are hearing. You could measure with your o-scope from the output towards the OPLL2 chip and check from where this triangle wave comes from?

I am searching on the internet to buy the IC2 (YM2420) PLL chip but I can't find it anywhere. Do you know If can I put a replacement part number?

[fenugrec]

Hello, I replaced the IC3 (AN7140) with a brand new but the same thing again. I will try to test the IC4.

Did you try any of our suggestions or are you just blindly replacing parts until it works ?

[2X]

You could try disconnecting the signal path somewhere just before the power camp - e.g. that 1uF/50V cap, or the 1K resistor, whatever is convenient. If it's still noisy, suspect IC3 or the supplies (less likely, the rails would have to be horrendously noisy to feed through the IC3). If no more noise, reconnect that 1uF and check earlier - maybe remove the two 10K between the OPL and IC4.

I was going to suggest to rule out the speakers and try with headphones, but that is a very large signal on the output and you risk causing damage. That 2V 50kHz tone has no business on the output...

I disconnect the "1uF/50V cap" and the noise was stopped.

[2X]

Hello, finally the problem was the AN7140... I have bought one from aliexpress where is not original. I bought one from ebay and works fine... noise gone. Thanks all of you for the help.