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Cobra 2010 GTL WX No dead key and no SSB swing.

Nov 15, 2015
5
0
11
61
Central Michigan.
Hello, I'm kind of new to the CB hobby and I'm really interested learning how to repair them. I recently acquired a Cobra 2010 GTL WX from a friend, who stated the it wasn't working properly and sure enough, I checked it out and on AM, there is no dead key or carrier but there is plenty of swing on the meter when I speak into the mic during TX —but when in SSB mode, either upper or lower side band, there is no swing on the meter. Any thoughts on what I should check first? It is equipped with the EPT014811Z board and the MB8719 PLL ic.

Thanks.
 
Last edited:

there is plenty of swing on the meter when I speak into the mic during TX

Um, which meter? There are two in this radio. One of them shows receiver signal level and transmit power when the mike is keyed. The other one is selectable to show modulation or SWR.

Do you have a wattmeter or SWR meter in line with the antenna? This is a pretty rudimentary starting point.

Microphones break more frequently than radios. A spare mike that you know is good can reveal if the radio is actually the culprit.

What kind of antenna are you using?

Have you ever attempted to repair a CB before? I would not recommend this model as a "first experience".

There is almost no technical info for this model.

Here is the owner's manual and a schematic online. [URL]https://web.archive.org/web/20...btricks.com/radios/cobra/2010gtl_wx/index.htm[/url]

If you have some experience with other SSB CB radios, there are things you can check.

If you have some basic tools, as well.

73
 
Um, which meter? There are two in this radio. One of them shows receiver signal level and transmit power when the mike is keyed. The other one is selectable to show modulation or SWR.

Do you have a wattmeter or SWR meter in line with the antenna? This is a pretty rudimentary starting point.

Microphones break more frequently than radios. A spare mike that you know is good can reveal if the radio is actually the culprit.

What kind of antenna are you using?

Have you ever attempted to repair a CB before? I would not recommend this model as a "first experience".

There is almost no technical info for this model.

Here is the owner's manual and a schematic online. https://web.archive.org/web/20190707111744/http://www.cbtricks.com/radios/cobra/2010gtl_wx/index.htm

If you have some experience with other SSB CB radios, there are things you can check.

If you have some basic tools, as well.

73
Um, which meter? There are two in this radio. One of them shows receiver signal level and transmit power when the mike is keyed. The other one is selectable to show modulation or SWR.

Do you have a wattmeter or SWR meter in line with the antenna? This is a pretty rudimentary starting point.

Microphones break more frequently than radios. A spare mike that you know is good can reveal if the radio is actually the culprit.

What kind of antenna are you using?

Have you ever attempted to repair a CB before? I would not recommend this model as a "first experience".

There is almost no technical info for this model.

Here is the owner's manual and a schematic online. [URL]https://web.archive.org/web/20190707111744/http://www.cbtricks.com/radios/cobra/2010gtl_wx/index.htm[/url]

If you have some experience with other SSB CB radios, there are things you can check.

If you have some basic tools, as well.

73
To answer a few of your questions, yes I do have experience working on 2 meter transceivers but not CBs. As for the meter in question, it's the SWR/Power meter on the right that I was reading and not the S meter on the left. The radio was in AM mode and the SWR/CAL/MOD switch was set for mod. The antenna I was using is a homebrew j-pole that is tuned and gives a SWR reading of 1:1 on ch.20, per my stand alone SWR meter. As for tools, I have about ten different soldering irons of various wattage's and I do have a multi-meter, oscilloscope, frequency, counter and signal generator, just to name a few. I was just hoping someone could point me in the right direction. I mean, should I be looking at the PLL circuit i.e. voltage, xtals etc... or at the finales?

KD8QAO
73
 
you can use the factory service manual for the 2000GTL for this radio.
there are some differences, but for this, they are the same radio.

i would start looking for the 7.8mhz signal from X4, and the area around TR31.
LC
 
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I would start by listening to the channel the 2010 is set to with another radio.

A coax jumper on the 'monitor' radio gets you a half-inch long sniffing antenna at the end of the jumper.

You should hear a weak signal in the monitor radio if the failure is in the power amplifier section of the 2010's transmitter.

If you don't hear anything at all holding the tip of the plug on the far end of the jumper near the 2010's transmit circuits the problem is upstream from the power stages.

The 7.8 MHz carrier oscillator is also used in sideband receive. If you have almost no SSB receive, that's the next place to look.

73
 
  • Like
Reactions: loosecannon
I would start by listening to the channel the 2010 is set to with another radio.

A coax jumper on the 'monitor' radio gets you a half-inch long sniffing antenna at the end of the jumper.

You should hear a weak signal in the monitor radio if the failure is in the power amplifier section of the 2010's transmitter.

If you don't hear anything at all holding the tip of the plug on the far end of the jumper near the 2010's transmit circuits the problem is upstream from the power stages.

The 7.8 MHz carrier oscillator is also used in sideband receive. If you have almost no SSB receive, that's the next place to look.

73
Thank you.
 

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