Question about Cobra 148 GTL 120-Channels Base CB Radio

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Cobra 2000 gtl

I just received a Cobra 2000 GTL from Ebay. When the radio is on there is a steady tone, similar to the sound of morse code is the speaker. The volume control has no effect on the tone. You can still hear other stations through the speaker, but the tone overwhelms it. I bought this radio used. It looks like someone tried to jump the PLL with the speaker switch, but they didn't change the PLL, it still has the MB8734. I removed the jumpers to the PLL.I plugged the speaker into all outlets, SP1, SP2, AUX, and even the headphone jack. Any help is appreciated. Thanks

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  • mr_mudduck Jul 05, 2008

    I have the same problem with my Cobra 148 GTL, When the radio is on there is a steady tone, similar to the sound of morse code is the speaker. The volume control has no effect on the tone. You can still hear other stations through the speaker, but the tone overwhelms it. It will also transmit this tone mixed with your own audio. I don't know if this is related but if I adjust the mic gain control the tone will change pitch. Have tried different working mic and your trick with the earth wire to the RX/TX mic pins and the tone is still there. Can you help?

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Cobra 2000
am carrier 4.4 volts will not ajust...ssb carrier will 3.5 volt will ajust but max out put is only 3.5 volts.losses all voltage at ssd carrier when switched to usd r lsb

Posted on Feb 05, 2010

Very low tx

Posted on Oct 31, 2008

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Hi,

It is a fairly common practice to make use of the CB/PA and/or speaker switch to modify this radio to add a few more channels (hot wiring the PLL pins). Perhaps your best option would be to rewire the unit back to factory specs. A schematic diagram would help you get them properly connected. This page is dedicated to Cobra 2000 GTL and have links to the schematics and other documents. This is of course assuming that you have a more than just familiarity with electronic components and circuitry, use of a DVM and a soldering iron (knowing the MB8734 is PLL) .

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Thank you for using FixYa.

Posted on Jul 03, 2008

I
i have yhe same problem
i have clear the contacts on ptt switch and the all contacts in the volume potentiometer

Posted on Aug 01, 2008

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