Realistic PRO-2020 Crackling

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Retired747

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Greetings,
I have just got my hands on a PRO-2020 by Realistic, there is a slight very faint crackling sound coming from the speaker that is audible when there are no transmissions. The crackling sounds is always there even when the volume is turned down to '0'.
Any suggestions or has anyone had the same issue and managed to fix it?

All hel appreciated

Eric
73's
 

krokus

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Greetings,
I have just got my hands on a PRO-2020 by Realistic, there is a slight very faint crackling sound coming from the speaker that is audible when there are no transmissions. The crackling sounds is always there even when the volume is turned down to '0'.
Any suggestions or has anyone had the same issue and managed to fix it?

All hel appreciated

Eric
73's
Sounds like a thermally sensitive transistor. Isolate it by using a can of "freeze spray" and replace it.

It could be a bad solder joint, which would show with tapping to board.

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Retired747

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Crackling PRO-2020

Thank you gentlemen I will try the 'Freeze' method..... I now have to find an electronic store that has the FREEZE spray. Radio Shack maybe? or EBAY as we live in a remote town and closest large town is 200Km away :-D
 

Engine104

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I have a similar problem with my Pro-2006, but the crackling noise is only on UHF and not VHF or 800 Mhz signals.

Can someone describe how to use freeze spray to identify the faulty component?

Tnx.
 

Ubbe

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the crackling noise is only on UHF and not VHF or 800 Mhz signals.
You have to figure out what is common for VHF and 800MHz. Could it be FM modulation on VHF and 800MHz and NFM in UHF?
But then the crackling level are probably following the volume control as it otherwise seems illogical?

When freezing something it contracts and shrink and often makes a change to the problem, either worse or dissapears. Spray one component at the time in the suspected area, in this case in the audio section where there are one or several big transistors or an IC circuit that is the loudspeaker amp and it's supporting components. Make the component white with frost while listening to the problem. Spray some more components until you hear a change. Then try to resolder that component and check if that helped. My experiance is that small SMD components often can be fixed by heating them up by resoldering.

Big tantal and electrolyt capacitors can dry out with time and are often the problem in old equipment. Sometimes there are capacitor kits being sold to replace all capacitors in old valuable equipment. There where also a scandal with pirated capacitors with bad specs that flooded manufactors assembly lines. I remember that at my workplace we bought 30 HP computers and 20 of them failed within a year where the capacitors had bulges or had blown on the motherboard. I also had a sound effects unit that failed after 2 years that had blown capacitors in the power supply. I think it was beginning of 2000 that these problems started.

/Ubbe
 

Engine104

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Dear Ubbe,

Thanks so much for your reply.

I have a copy of the service manual. I'll check to see what components are part of the UHF circuitry and go from there with the freeze spray.
 

Ubbe

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I wouldn't go for the UHF circuit with my first try. If the crackling is independent of volume setting then look at circuits between volume control and loudspeaker amp. If the crackling level follows volume control then look between FM discriminator and volume control in the schematics.

The Pro2004, and pehaps Pro2005, had some problems with solder joints but shouldn't be a problem with the Pro2006 if the soldering haven't oxidized. But you'll find the problem area anyhow when spraying the components.

/Ubbe
 

krokus

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I wouldn't go for the UHF circuit with my first try. If the crackling is independent of volume setting then look at circuits between volume control and loudspeaker amp. If the crackling level follows volume control then look between FM discriminator and volume control in the schematics.
Agreed. These noises are going to be somewhere in the audio portion, after it is recovered from the RF.

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Engine104

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Thanks guys.

The crackling noise on my 2006 is evident only on UHF. Everything else (VHF, Lo band VHF, Civ & mil air and 800 Mhz) sounds clean. It is independent of the volume control. It doesn't make a difference with the internal speaker or external speakers.I haven't tried the headphone jack. I think I'll give that a go tonight.
 

krokus

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Thanks guys.

The crackling noise on my 2006 is evident only on UHF. Everything else (VHF, Lo band VHF, Civ & mil air and 800 Mhz) sounds clean. It is independent of the volume control. It doesn't make a difference with the internal speaker or external speakers.I haven't tried the headphone jack. I think I'll give that a go tonight.
Is that on any VHF signal, or just one?

Since it is just one band, that limits the options of what can be easily fixed.

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Engine104

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Is that on any VHF signal, or just one?

Since it is just one band, that limits the options of what can be easily fixed.

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I think you meant UHF? That's where the problem is. No, all local agencies on UHF here in Los Angeles (LACoFD, LASD and others) and 440 ham have the crackling noise.

I thought it could be some local noise source, so I took the 2006 to work, which is 30 miles from home, and the problem was still there.
 

krokus

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I think you meant UHF? That's where the problem is. No, all local agencies on UHF here in Los Angeles (LACoFD, LASD and others) and 440 ham have the crackling noise.

I thought it could be some local noise source, so I took the 2006 to work, which is 30 miles from home, and the problem was still there.
Yes, UHF. Ok, then it sounds like some type of LO, or RF amp, issue. The rest of the paths are most likely common.

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Engine104

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Yes, UHF. Ok, then it sounds like some type of LO, or RF amp, issue. The rest of the paths are most likely common.

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As Clint Eastwood once so famously said, "It's a wise man who knows his limitations" :) My radio tech expertise is pretty limited.

I use my newer handhelds for most stuff now, so fixing the 2006 isn't critical. I may end up shipping it off and let Gerry at G&G work on it at some point.

Thanks so much for your help.

73,

-Larry (KG6EJT)
 
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