Image

Cobra 142 gtl no transmit

Have some other technical questions can't find the answer for? Come in and ask them here.

Moderator: JR Moderator

User avatar
nineball
Super Mud-Duck
Super Mud-Duck
Posts: 9
Joined: Friday, 21 January 2011, 22:42 PM
Name: nineball

Cobra 142 gtl no transmit

Post by nineball » Monday, 07 March 2011, 0:06 AM

Hi, I have a cobra 142 gtl I have been tring to get going and have tried about everything like new finals, new audio chip, new regulator, some new caps. Has 12 volts at driver final key the mic and goes to 0 volts. Any info at all would help me and thanks to all of you.


User avatar
TheCBDoctor
Sponsor
Sponsor
Posts: 2811
Joined: Friday, 13 March 2009, 13:54 PM
Radio: HR 2510
Name: Rick
Referrals: 4
Contact:

Re: Cobra 142 gtl no transmit

Post by TheCBDoctor » Monday, 07 March 2011, 7:50 AM

Hi nineball

Does the radio transmit on Sideband? The power source to the Final and Driver is the AM modulation circuit. That would be the Transistor mounted on the right rear side to the radio's case. It is a common NPN transistor. The voltage should be about 6 volts on AM and is referenced and clamped to 13 volts on Sideband.

If the radio works on Sideband then that is the problem. Is there any modifications to the radio?

http://thecbdoctor.net/_mgxroot/page_10783.html

Respectfully,
Best Regards,

Rick, The CB Doctor


OFFICIAL SPONSOR - http://www.thecbdoctor.net/" onclick="window.open(this.href);return false;
Image



User avatar
nineball
Super Mud-Duck
Super Mud-Duck
Posts: 9
Joined: Friday, 21 January 2011, 22:42 PM
Name: nineball

Re: Cobra 142 gtl no transmit

Post by nineball » Monday, 07 March 2011, 23:06 PM

The radio does not transmit at all even on sideband. Howerver the pa does work and the light changes from green to red when keyed. It receives very well, just cant get any output at all. Nothing on the meter either.

User avatar
TheCBDoctor
Sponsor
Sponsor
Posts: 2811
Joined: Friday, 13 March 2009, 13:54 PM
Radio: HR 2510
Name: Rick
Referrals: 4
Contact:

Re: Cobra 142 gtl no transmit

Post by TheCBDoctor » Tuesday, 08 March 2011, 16:13 PM

Hi nineball

Measure the voltage on the center pin of the final and see if you have 4 to 6 volts on AM and 13 volts on SSB. If you do; I would suspect a bad Final. Do you have another radio that receives? If so, put that radio next to your Cobra 142 GTL and see if you get any indication of transmit.

The pre-driver should cause the meter on the other radio to show some signal. If you do not see anything, then the problem will not be that simple.

http://thecbdoctor.net/_mgxroot/page_10783.html

Respectfully,
Best Regards,

Rick, The CB Doctor


OFFICIAL SPONSOR - http://www.thecbdoctor.net/" onclick="window.open(this.href);return false;
Image



User avatar
nineball
Super Mud-Duck
Super Mud-Duck
Posts: 9
Joined: Friday, 21 January 2011, 22:42 PM
Name: nineball

Re: Cobra 142 gtl no transmit

Post by nineball » Thursday, 10 March 2011, 22:22 PM

Did what you said and it has less than 2 volts on the center leg of final and does show modulation on other radio's meter on sideband but not on am.


Post Reply Previous topicNext topic

Who is online

Users browsing this forum: Google [Bot] and 1 guest