Question about Uniden PRO510XL 40-Channels Base CB Radio
My Uniden Pro510 XL CB radio has reduced rf output. As the transmitter is held on the output starts out at about half power and slowly decreases. Also it will go into a "motorboating" condition when modulated or when the power level decreases and it is keyed on again. I have replaced several of the electrolytic capacitors, but the problem persists. It is transmitting and modulating on the proper channels, and the receiver seems to be normal. Hope one of you techs have had experience in working on this model. Thanks. Bob W.
Based on your post/description, I am assuming that:
1. The standard Uniden microphone that came with the radio has not been replaced with a power microphone;
2. The amplitude modulation method (transformer) is not modified;
3. The Power Output has not been modified;
4. The radio is not being used in a Rife/bare system.
Your posted problem may be caused by:
1. Mic. You can verify if your mic is causing the motorboating by grounding pin#3 to transmit without any input audio/mic connected; with pin#3 grounded and no audio in, determine if you still have the motorboating problem. If no then chances are its the mic, if yes, then its internal to the radio;
2. Audio amplified IC and/or its associated components. Check the audio amp is TDA1905, capacitors C50 to C58;
3. AMC (amplitude modulation control). VR2, Q6 likewise check the Limiter Q5.
In some versions, a microphone with an Electret Condenser Microphone Element is used. This type of mic uses 2.8~3.3 volts DC from the radio. These versions may use the audio line (pin#2 in a wire pin mic plug) or a separate +3V mic power (in a 5 or 6 pin mic plug). Motorboating then may be further caused by the dropping resistor that has gone up in value or by the capacitor after the resistor that has lost its capacitance along the +3V line. Indication low or no +3 in pin#2. In some instances, the +3 goes down when talking into the mic.
Hope this be of help/idea. Pls post back how things turned up or should you need additional information.
Good luck and kind regards.
Posted on Jan 19, 2008
It sounds like your circuit board may have a bad solder joint. Sometimes during manufacture of the ciruit board, the joint could not be perfectly made. This will limit conduction and create heat which will worsen the effect over time. If you are familiar with opening and working with electronics then I suggest you remove the circuit board and inspect it for cold solder joints. When you find one, you can use a Cigar Torch type lighter to help reflow the solder easily. Out side of that, you mayu want to send it to a Electronics repair shop to do this for you. Let me know more and I will help. Good luck
Posted on Jan 19, 2008
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