Uniden Bearcat BC 560XLT Scanner question

[MrBruce]

Hello, I am new this forum and have looked for some information on this forum but failed to find the information I wanted. I am hopeful that someone who frequents this forum board can answer my question.

I have a Uniden Bearcat BC 560XLT scanner. I had a resister burn up and the scanner lost it's ability to receive any of the frequency bands it is designed to receive.

I do not know what value the resister was, so I replaced it with a common resister value of 100 Ohms. The bands still fail to receive any of the bands. I have used a signal generator and it appears that one of the IF stages is still operative, however I am sure the mixers are out of commission.

I have a schematic diagram of the scanner, the problem I am faced with is that Uniden did not mark the printed circuit board for the resistor part numbers. There is simply a marking for the resistors but no part numbers such as R1 or R15. I have tried unsuccessfully to find a printed circuit board map, so I can at least identify which resistor it is. I do know the resistor is in the power circuitry which includes the on-off switch and IC6 which is the IR3M03A chip.

The resistor is located right next to the D5 which is a diode.

What value in Ohms is this resister? If anything at least post the color bands.

Thanks in advance.

Bruce.

 

[MrBruce]

Just adding to this topic that the Radio Shack Pro-2025 scanner has the same board, so if anyone has that scanner please let me know what the value of that resistor is that I quoted in my first post.

Thanks in advance.

Bruce.

 

[tonyclark]

Took mine apart, It's brown- black- red
Hope you get it working

Charles

 

[MarkWestin]

When a resistor burns up it is always a symptom of a problem and not the problem. The odds are good that as soon as you replace the resistor and turn the scanner on the resistor will burn up again. You need to figure out which active component (diode, transistor, or Integrated Circuit) has failed and is causing the resistor to burn up.

Best of luck with your troubleshooting

Mark

 

[MrBruce]

Thank you for your replies and the resistor color code.

I have uprooted all of the diodes and all tested about 10 Ohms red probe to band end and no ohms reading with black probe to banded end of all of the diodes.

There are two other active components there is the L7808CV voltage regulator which checked out fine then there is the IR3M3A IC made by sharp, which is difficult to find data in English if any exists at all.

The scanner turns on and FM white noise is heard through the speaker. I tried the weather frequencies which has a continuous carrier, they worked before this resistor burned up, now they do not. There is a resistor already in the circuit I put a brown black brown 5% tolerance 1/2 Watt resistor in place of the burned one. This resistor has not burned up and no components are running hot. Now where D10 is soldered into the board, there is a slight appearance on the circuit board where D10 sits, that heat had built up at some point and slightly charred the board. Right now the component is cool and was tested and appears to be a good part. In fact all the diodes passed the Ohm meter test.

I will try a resistor @ 1,000 Ohms which is brown black red ---Thanks Charles for that color code.

Anyone have any idea where the data is for that IR3M3A?

Bruce.

 

[pro92b]

The equivalent for the IR3M03A is MC34063. Datasheet at http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF

 

[MrBruce]

Pro92b, thank you very much for the data sheets. I knew I would find some professional answers at this forum board and I was right about that thought.

I'll keep everyone updated on my progress. I do not know what the original owner of this scanner paid for it, but I must say, the parts on this board are very limited. Can't be more than 50 parts total.

Bruce.

 

[bbradio]

uniden bearcat bc 560xlt schematic

Please help (MrBruce) or anyone else who might have the schematic that could email it to me at bbradio@att.net or bbradio@suddenlink.net I have either a short or cold solder joint on the squelch