Pro-197 is microphonic

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maynardjames

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Hello all just as the title says my pro-197 is microphonic. I am a feed provider and I don't want my listeners to hear whats going on in my house lol HELP!! Ive tried a new patch cable I also tried switching from the ext speaker jack to the headphone jack with no such luck. When I plug a set of headphone in and tap on the scanner I can hear it in the headphones as well. Is this a grounding issue maybe? I aslo disconnected the internal speaker as well to see if that was the problem with no such luck either.
 

techman210

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It’s likely an oscillator that’s causing the problem.

you’ll have to open it up, tighten down all the internal screws and see if it goes away. If not then with something insulated tap around the board until you find it. It’s probably going to be under a metal shield. Check and see if any of the solder is broken that secures the metal shield to the printed circuit board.

If resoldering does not fix it, you’ll have to figure out a way to make something to constantly apply pressure to that, so it is no longer affecting the radio.
 

buddrousa

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Let me guess your feed computer is a laptop. If this is right turn off the MICROPHONE on the laptop.
 

prcguy

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If you don't have a live microphone active by mistake then all the info below is good. Its typically a VCO coil or related component that is very sensitive to vibration and these are usually glued down at the factory with some wax or hot glue, etc, and the glue has come loose. Sometimes tapping on the board as mentioned will usually find it.

It’s likely an oscillator that’s causing the problem.

you’ll have to open it up, tighten down all the internal screws and see if it goes away. If not then with something insulated tap around the board until you find it. It’s probably going to be under a metal shield. Check and see if any of the solder is broken that secures the metal shield to the printed circuit board.

If resoldering does not fix it, you’ll have to figure out a way to make something to constantly apply pressure to that, so it is no longer affecting the radio.
 

maynardjames

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Let me guess your feed computer is a laptop. If this is right turn off the MICROPHONE on the laptop.
No it's a desktop. I need it to come back on after a power failure and auto start radio feed and to my knowledge no laptop does this. Its microphonic without being attached to a computer as well, I can hear when I handle the chassis in the headphones
 

maynardjames

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It’s likely an oscillator that’s causing the problem.

you’ll have to open it up, tighten down all the internal screws and see if it goes away. If not then with something insulated tap around the board until you find it. It’s probably going to be under a metal shield. Check and see if any of the solder is broken that secures the metal shield to the printed circuit board.

If resoldering does not fix it, you’ll have to figure out a way to make something to constantly apply pressure to that, so it is no longer affecting the radio.
Thanks I'll bust out the chopsticks and start applying pressure around the board.
 

maynardjames

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If you don't have a live microphone active by mistake then all the info below is good. Its typically a VCO coil or related component that is very sensitive to vibration and these are usually glued down at the factory with some wax or hot glue, etc, and the glue has come loose. Sometimes tapping on the board as mentioned will usually I don't have any microphones on the computer so ill check out the internals
Have you tried to turn off the MICROPHONE just to try it.
Yes I've turned off the mic,line in and cd player and no effect.
 

prcguy

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Gently tap on everything inside the radio that looks safe to tap on. Putting pressure on things might make a crunching noise in the speaker but for a microphonic part you need to tap and that will eventually make a loud ticking noise in the audio when you hit the right area.

Thanks I'll bust out the chopsticks and start applying pressure around the board.
 

maynardjames

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Looks like this little guy is the culprit. When I press I can hear a hum and no matter which way I press the scanner stays microphonic. When I rub the stick across the component it sounds like if you were to rub your finger across a microphone's diaphragm. It sits under the CN3 VOL plug so I can't get to the legs to see if it's a cold joint. Could I put glue on it to at least muffle the sound? Its beyond my skill level to attempt to change it out.
 

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jonwienke

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The component you're touching with the stick appears to be a capacitor. It only has two solder connections, one at each end. Remelt the joints one at a time, and that might help.
 

ramal121

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Is that the only place it seems sensitive? Maybe if you can photograph the flip side of the board and point to the spot where the microphonics are the worst.

It is caused by mechanically modulating the VCO. The tuning changes by the vibration applied to it and is demodulated like any FM signal and heard in the speaker.

Cleaning, tightening, resoldering are all good suggestions. I have also reduced microphonics by "potting" components. I prefer a hot glue gun as it is fairly inert and can be removed later if desired.
 

maynardjames

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There is no change in the sound when turning the volume or squelch knob it remains constant. I can hear the tapping everywhere on the scanners main board and chassi not so much on the board behind the face plate. I've also unplugged the the vol plug from the board and it's still microphonic. Here is a picture of the board I found online and I circled the spot on the back side of the component that's suspect. Also when I press on the white plug its equally microphonic as the capacitor.20191022_195403.jpg
 
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