Uniden PC122Xl Mod Limiter Location?

[Mudfoot]

Where's the mod limiter at in this radio? Trying to find out if it's been molested. My eyes are sore from scanning.

Thanks.

 

[ExitThirteen]

Look for TR27, it should be located near the front right part of the main PCB, relatively close to where the mic jack is at. Should be labelled C945 on the transistor. Hope this helps!



~Cheers~

 

[Mudfoot]

Thanks a bunch. I'll check when I get back home in couple days. Wished I'd brought it with me.

Thanks

 

[ExitThirteen]

No problem, let me know how you get on when you get back to the homefront.


~Cheers~

 

[sp5it]

Removing TR27 is bad idea. You will disable ALC. R153 will disable limiter in AM only.
Mike

 

[Mudfoot]

I'm just making sure the previous owner didn't do anything. I've had this packed away for years. It looks damn near new. I remember talking to a friend when I first got it and said audio was crappy. I'm just thinking that the original stock mic is the culprit. I hope...

 

[melaza]

Uniden PC-122 Miscellaneous Data Service Section How-To Manual


<gotproof><gotproof>:headbang

 

[MudDuck442]

I think TR53 is AMC only

 

[Mudfoot]

So..

Look for TR27 and TR53?

 

[MudDuck442]

Yes, more or less. On most radios there is a "main" limiter which usually shunts the mic audio depending on the voltage to the base of the transistor. This or part of the circuit will disable the ALC and AMC. Other parts of the circuit will only disable the AMC for AM only. It just depends on how the radio is set up. What I have seen in some radios is where someone has removed the main limiter and other parts of the circuit as well. That means they usually have been to a butcher who didn't understand how the circuit works at all. Usually I start with making sure I have ALC control and that means the main limiter is intact...usually. Also people like to do resistor changes too in the mic circuits..usually in the 148 chassis where they change R124 and R126 which only overdrives the mic preamp and also messes up the ALC time constant even if the limiter isn't removed. So why SSB will usually be OK sounding even if R131 or TR26 (AM AMC) is left intact because the circuit time constant is wrong the ALC for SSB no longer works right resulting in lower average power output. Another one is where people add resistance to the base of the liimiter. Once again the all too popular add a 1K resistor the the middle leg I have seen done. Same thing. The transistor will not conduct or conduct too much if not done right. I have seen this done of the chassis you are working with as well so make sure it hasn't been messed with too much if at all. People also like to adjust bias current on the driver and final for more power out without knowing what they are doing too which can make SSB take a dive.