Question about Cobra 148 GTL 120-Channels Base CB Radio
Without having a look inside of radio. but sounds like the voltage req chip on the side of radio.i think off hand its mb3756 .yes just got out manuel this one .usually causes problems like your one.email back.cheers from new zealand..rick.
Posted on Feb 20, 2008
Tomcat 1 back ...i have found the fault no modulation on am/usb/lsb.tr -23 a bc458 transister .replaced this transister and wow modulation on all 3 modes thanks zeppfrog for telling me where to look .
Posted on Mar 01, 2007
Ok collector of tr-23 reads 1 volt with a dead key or without the dead key .the r-120 reads 6.5v with a dead key or without a dead key .i have replaced the capacitor 330uf to a 16v.replacing tr23 could be at fault.end of press for now i will get back..
Posted on Feb 25, 2007
Yes i remember some tec said sometimes people add a power mic and dont wire it right get modulation wire wrong and feedback .wrong wiring blows out the c18 electrolytic capacitor .thanks zeppfrog thanks for the help i will do some testing.i replaced the meter light and the tx light with the a cool blue led it looks smart.i will get back with the results.
Posted on Feb 23, 2007
I am having this trouble as well. The ics was my thought too, but I think it is in the modulation circuit somewhere. another article i read said to check this. "Look for the collector of TR-23, you should read about 4.5 V with a dead key. If you find that this voltage is not present, check on the opposite side of R-120 for 6.5V. Most likely this voltage will not be present; if this is the case, C18 has shorted and needs to be replaced. This is a 330uf, 10V electrolytic capacitor beside L31. To prevent "future" problems, replace with a 16V unit." As of yet, i havent gotten that far. note this is from the cobra 2000, but they are very much alike. you might cross check the resistor capacitor numbers though. btw, isnt the mb3756 the pll ic?
Posted on Feb 15, 2007
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