Tuner whistle noise in FM

[Palaka]

A high pitched noise just started with FM in SX-980. Sound frequency is 4.468 kHz. Starts after running normally for between 5 and 30 minutes. I am going to be checking the FM path for signal and voltages but maybe someone has an idea what this is? thanks! audio via youtube. frequency histogram with 4.468 kHz spike attached.

 

[Palaka]

A high pitched noise just started with FM in SX-980. Sound frequency is 4.468 kHz. Starts after running normally for between 5 and 30 minutes. I am going to be checking the FM path for signal and voltages but maybe someone has an idea what this is? thanks! audio via youtube. frequency histogram with 4.468 kHz spike attached.

Update: I can bring on the noise by freezing spray on PA3001A where the noise was present on its output pin 6. Replacing the IC.

 

[Palaka]

Update: I can bring on the noise by freezing spray on PA3001A where the noise was present on its output pin 6. Replacing the IC.

IC replaced. All is good. Mischief managed.

 

[Palaka]

IC wasn't the cause. Maybe solder needs to be reflowed somewhere upstream in the front end.

 

[Warren-Oates]

Sounds like something is getting warm and failing, have you tried your freeze on other parts?

 

[Palaka]

Sounds like something is getting warm and failing, have you tried your freeze on other parts?

I think so too but sometimes it takes a few months of use. And turning it off then on and it usually goes away. It will get a closer look at the front end and near by components.

 

[Warren-Oates]

Next time it starts, switch to Mono and see if the noise goes away. That should help narrow it down.

 

[Palaka]

Next time it starts, switch to Mono and see if the noise goes away. That should help narrow it down.

S9 is the mono stereo switch. It takes L and R signal from all inputs and shorts them in mono. Why do you think this would effect a signal output from the IF gain IC?

 

[Warren-Oates]

I don't know that it would at all, just ruling out the Stereo decoding process. I have only had one fm tuner make a sound close to that, it was a Realistic receiver, and it only makes the strange distortion when it locks on to a stereo signal, I push mono and the sound is normal.

I'm pretty sure you are much smarter than I when it comes to tuners. Not sure if you are aware but there is a forum here on AK for Tuners, if you don't crack this here in the Pioneer forum, you might try the Tuner forum. I have hunch somebody has heard that strange sound before and knows exactly what is failing.

 

[Palaka]

I don't know that it would at all, just ruling out the Stereo decoding process. I have only had one fm tuner make a sound close to that, it was a Realistic receiver, and it only makes the strange distortion when it locks on to a stereo signal, I push mono and the sound is normal.

I'm pretty sure you are much smarter than I when it comes to tuners. Not sure if you are aware but there is a forum here on AK for Tuners, if you don't crack this here in the Pioneer forum, you might try the Tuner forum. I have hunch somebody has heard that strange sound before and knows exactly what is failing.

your realistic issue was related to the MPX demodulator IC. Mine was on or before PA3001A where the noise was present. It is a mono signal until it gets to the MPX chip.

 

[AE Bob]

I have seen several Pioneer receivers (and others) that squeal in FM, usually near the bottom of the dial. The issue is caused by a feedback loop through the tuning capacitor shaft, feeding RF from the last RF stage back to the first through the tuner shaft. This occurs because the small brass ground brushes are not making a good connection to the shaft. Cleaning the shaft contacts cures the issue. When the squeal starts what happens if you tune off the station (with the FM muting off)?

 

[Palaka]

I have seen several Pioneer receivers (and others) that squeal in FM, usually near the bottom of the dial. The issue is caused by a feedback loop through the tuning capacitor shaft, feeding RF from the last RF stage back to the first through the tuner shaft. This occurs because the small brass ground brushes are not making a good connection to the shaft. Cleaning the shaft contacts cures the issue. One the squeal starts what happens if you tune off the station (with the FM muting off)?

The 4K sound occurs through the entire FM frequency span of the dial. But it makes sense to look closely at the tuning capacitor as you suggest. Sometimes it doesn't happen for days. Anyway, I sold the receiver with this known issue so another person can do some more troubleshooting. Thank you for your reply.