Cobra 25NWLTD Issues

[Dt0M1776]

Hi all, new here, been browsing for a few weeks. I have a cobra 25NWLTD that intermitenly stops transmitting and receiving and i just hear a very low tone of a buzz. when this happens the needle on the meter pegs all the way to the left and will not move even when i key the mic. then suddenly every few minute it will work again for a bit. Since doing more research on this site I am in the process of installing a 108 inch wipe and re wiring the radio straight to the battery, a power mic is also on the to do list. I plan on getting a new radio with SSB in the future but would like to make the cobra work in the mean time. Another question I have is about the whip i am installing. I have the radio shack 102 incher and purchased the GP riser and corona ball. the whip has a factory ball on it that looks like it needs to be cut off tp remove it. If i cut it and install the new ball, do i need to cut enough off to have the complete length with the new corona ball be 108 inches or does it make a difference if the new ball adds a little length? The whip is mounted on the bed side of the left rear stake pocket with a custon made bracket and i am in the process of bonding all the panels to each other and the frame.

Thanx

 

[Dt0M1776]

oh yeah forgot to mention. the current antenna is a 36 inch fire stick and i noticed upon removal the coax inner wire running to the element is cracked and the wires are exposed in a few places in the short run between where the coax is stripped back and it connects to the antenna. so could this cause the problem i've been having?

 

[Sideways]

Definitely replace your coax, then see if the issue continues.

After you get everything mounted the way you want it, use an swr meter to find the correct whip length. Cut or add length to the whip to achieve lowest possible swr.

 

[Dt0M1776]

OK got the new whip installed with new mini 8 coax. Reception is amazingly better but the radio still goes dead after a few minutes. No recieve and no transmit. The needle on the meter just stays buried to the left a 0. Then magically it will start working again. What are some things I can check to troubleshoot this?

 

[Robb]

Might have a short in the mic's plug. That would explain the buzzing on transmit. Try another mic if you have one. Might have to take apart the mic's plug and see if a wire is torn and shorting.

 

[sonoma]

if the mic is good the next thing would be check for cold solder joints inside the radio.

 

[Dt0M1776]

Not positive but I don't think it's the mic. I plugged in a speaker to PA when this is happening and it works. Also saw the service bulletin for loose pic board screws... checked those and they were loose but it didn't solve the problem

 

[Dipole]

Sounds like you have a Cap going bad in the audio amp. as current passes through it it gets hot and expands internally causing a dead short (the buzzing noise) as it cools it contracts making contact again allowing the audio to pass.

 

[Sideways]

OK got the new whip installed with new mini 8 coax. Reception is amazingly better but the radio still goes dead after a few minutes. No recieve and no transmit. The needle on the meter just stays buried to the left a 0. Then magically it will start working again. What are some things I can check to troubleshoot this?

If the mic isn't the problem, I would say its a bad solder joint as sonoma said.
Take the top cover off the radio, use a plastic screw driver, ink pen, or something non-conductive and probe around on the solder joints near the pll area, behind the channel display.
Do this as the radio is acting up, and see if it starts working again.