cobra 138xlr (low power output)
cobra 138xlr (low power output)
I have a cobra 138xlr with low output power.to start with i changed the finals and am power regulator. i ajusted l-39,l37,l32 and l30. I still have low output power. the receive works, upper and lower side band also has low output power. when i key up the radio it only goes to 1 watt. I would appreciate if someone can please give me a hand with this radio. thank you, galaxy
Re: Cobra 138XLR Low power output.
Check L43, L44, R179 and R199 they could be open circuit, if not open circuit let us know what the voltage is at the base of the driver TR44 and the base of the final TR43.
Rick.
Rick.
Re: Cobra 138XLR Low power output.
thank you for your fast reply rick,,, i checked voltages on tr 44= 22 volts, tr 43 = 14. i also changed c- 179 to a 2.2 uf at 50 volts. then i adjusted it again ,, it went up to 3.5 watts. galaxyRick wrote:Check L43, L44, R179 and R199 they could be open circuit, if not open circuit let us know what the voltage is at the base of the driver TR44 and the base of the final TR43.
Rick.
Re: Cobra 138XLR Low power output.
early today i was checking voltage, a wire came off the pa , (a brown wire with rf chock)and lost audio. i can't find where the wire goes to. i hope did not blow the audio chip? galaxygalaxy wrote:thank you for your fast reply rick,,, i checked voltages on tr 44= 22 volts, tr 43 = 14. i also changed c- 179 to a 2.2 uf at 50 volts. then i adjusted it again ,, it went up to 3.5 watts. galaxyRick wrote:Check L43, L44, R179 and R199 they could be open circuit, if not open circuit let us know what the voltage is at the base of the driver TR44 and the base of the final TR43.
Rick.
Re: Cobra 138XLR Low power output.
Is the power output OK now? The wire which has come off sounds like its come off the the CB/PA switch if it is the one coming from the ext speaker socket vir a choke it go to the CB/PA switch.
Rick.
Rick.
Re: Cobra 138XLR Low power output.
it's still low out, yesterday when i was adjusting i lost audio,know today i have audio,i think something is not right.. i need your help,ssb works great. this radio was widebanded, is that why i can't get more out put . thank you , galaxyRick wrote:Is the power output OK now? The wire which has come off sounds like its come off the the CB/PA switch if it is the one coming from the ext speaker socket vir a choke it go to the CB/PA switch.
Rick.
Re: Cobra 138XLR Low power output.
What is the output power on SSB? Did you check L43, L44, R179 and R199?
What is the Base voltage at the Driver and Final, last time you gave me the Collector voltage.
Why do you keep putting my quote in your message, what is the point.
Rick.
What is the Base voltage at the Driver and Final, last time you gave me the Collector voltage.
Why do you keep putting my quote in your message, what is the point.
Rick.
Re: Cobra 138XLR Low power output.
Try replacing the driver and retuning but do not adjust L30 as this is the 54 MHz trap and should never be adjust, also reset the bias on the driver and final.
What is the PCB number?
Rick.
What is the PCB number?
Rick.