Pro-26 Appears To Operate Normally But Only Buzzing Audio Via Speaker And Headphones

[Vincentz]

I'm the original owner of a model 20-506 Pro-26 from 1995. It has seen light use over the years and was working properly a few months ago. I had stored it without batteries and when I popped them in and turned it on I got a buzzing sound as it scanned through all 10 banks of blank frequencies. I don't recall it losing all stored frequencies before when left without batteries.

When I turn it on, the buzzing tone it produces can start as high as 210 Hz but after turning it off and on a bit it starts at 150 Hz and drops to about 110 Hz in around 10 seconds. As I turn the scanner's volume up the frequency goes down to between 75 Hz and 85 Hz and stays there for a bit before slowly dropping down through 65 Hz. If I turn the scanner off and then back on again after this, the initial frequency starts at around 105 Hz.

So turning up the volume lowers the frequency and leaving it running lowers the frequency. Something is drawing down power.

One of the first things I tried were a fresh set of batteries but it made no difference. I can't find my AC adapter to see if that makes a difference.

I programmed in a few frequencies and let it scan through them. It looked normal, stopping on a frequency and then scanning on like it typically does. It just doesn't let me hear anything except that tone all the time. It is the same with earbuds plugged in, so it isn't a problem with the speaker.

Attached is a Zip of a Wav file of the sound.

Anyone have an idea of what's going on here? There is an airshow near my house for the next two days and I was hoping to hear ATC etc. I'd like to know if this thing is resettable or repairable or if I have to replace it.

Woah! And just for about 30 seconds the scanner seemed to be working normally. Now it is back to the buzzing sound.

Any insight would be greatly appreciated.

 

[tvengr]

What is your city, county, and state and which frequencies are you monitoring? If you are hearing a buzz, the frequencies may have switched to digital.

 

[CycleSycho]

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The scanner could have an oxidation issue on a/few of its connections throughout your scanner based on this in your original post "Woah! And just for about 30 seconds the scanner seemed to be working normally. Now it is back to the buzzing sound." I'm not familiar with this particular radio's innards but maybe you could look for corroded pin(s) or oxidation on the soldered side of the PCB (including a bad solder point(s). If that isn't the case, maybe some oxidation worked its way into the headphone/external speaker jack or the 'pot' on the volume or squelch controls. Hope it is as simple a find. Good Luck!


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[buddrousa]

Sounds like it could be the filter capacitor in the power supply circuit.

 

[Vincentz]

What is your city, county, and state and which frequencies are you monitoring? If you are hearing a buzz, the frequencies may have switched to digital.

I live in Abbotsford, BC, Canada, but the buzz is on all frequencies and is continuous even when scanning channels and not tuning any one in particular. That suggests to me it isn’t an issue of a digital signal but something wrong in the scanner itself.

.
The scanner could have an oxidation issue on a/few of its connections throughout your scanner based on this in your original post "Woah! And just for about 30 seconds the scanner seemed to be working normally. Now it is back to the buzzing sound." I'm not familiar with this particular radio's innards but maybe you could look for corroded pin(s) or oxidation on the soldered side of the PCB (including a bad solder point(s). If that isn't the case, maybe some oxidation worked its way into the headphone/external speaker jack or the 'pot' on the volume or squelch controls. Hope it is as simple a find. Good Luck!
.

Thank you for the suggestions. I'm not seeing anything obvious. I have done some basic soldering like replacing large capacitors on a computer display circuit board but anything this fine is beyond my ability to test and repair. I expect I will need professional service at this point. I don't know whether it is better to find a local business or try some scanner specific centralized repair service.

Thanks again.

Sounds like it could be the filter capacitor in the power supply circuit.

I found a service manual for the Pro-26 but I can't interpret it well enough to even know where that component would be.

What you are saying certainly makes sense to me, even given my limited understanding of electronics and circuitry.

Thanks for the reply.

 

[tvengr]

If the tone varies with volume, it could be a bad decoupling capacitor. It sounds like the scanner is breaking into oscillation. There may be a large filter capacitor directly across the batteries.

 

[G4ZKR]

Have you found the fix for your problem?
I am about to start, on a friends pro-26, to try and find the cause of the same symptom you posted.
It would be really great if you have a fix it would save me a lot of time and as I'm not great with SMT components probably the pcb as well.
cheers.

 

[Vincentz]

Have you found the fix for your problem?
I am about to start, on a friends pro-26, to try and find the cause of the same symptom you posted.
It would be really great if you have a fix it would save me a lot of time and as I'm not great with SMT components probably the pcb as well.
cheers.

Unfortunately I haven't found a solution.

I've just put it aside until I can find someone who can service it for me.

If you do figure out a solution I'd be grateful if you'd share it back here.

Vincentz

 

[wtp]

i had some older radio shack stuff do weird things like this.
sometimes it would scan and get no audio.
so kind of in a fit i put it on its back and gave it CPR and it worked.
i think that was the pro 92
the pro 32 was always fine and the pro 34 i would 'twist'
so you might give it a CPR move or twist it, sounds like nothing to loose.
the reason i thought of this is that there is two circuit boards connected with square 'pins' from board to board.

 

[jmn]

I had the same problem with my 'unused for years' PRO-26. I opened up the back and re-seated
the board as someone else suggested in a different thread. This didn't 'fix' the problem. So I dug
out the 9V DC supply, plugged it in, scanned for my local NOAA/NWS WX frequency, and put
in an audio plug to silence the speaker. I then set it aside while powered-on. Occasionally, I
checked to see if the motorboat was still around. However, after I couple of hours, the motorboat
seemed to have moved on and the PRO-26 seems to be working properly.

Hope this helps!

 

[alfonso]

hello
check IC,TDA7233D AUDIO PWR
lucky