Question about Cobra 19 DX III 40-Channels Base CB Radio

1 Answer

President mckinly ssb/am model with mb8719 pll chip.

Fault finding need help..transmitt carier on am normal 4 watts no modulation on am and no modulation on ssb usb/lsb.receive is alright.checked mic insert -inside mic etc and other end mic plug all ok their.

Posted by Anonymous on

  • Anonymous Aug 03, 2007

    fuyt back .found predriver 2sc1906 was blown replaced with 2sc1966.final ok.noticed now that the final and driver had 13 volts readings on the base .when switching mode switch am should read 5.50 volts when switch mode switch usb/lsb should read 13.75 volts.checking tr41 dc reg transister also tr42dc reg transister end of press i will be back ......

  • Anonymous Aug 03, 2007

    fuyt back tonight 11.20pm been in the garage working on the cb radio put back ic6 found that i could hear my modulation my voice on all modes lsb/usb/am connected another cb radio besides the president radio .mod was low not even moving the needle but i could hear myself looked inside cb again from the mic gain control 2 wires going into the amp stage tr 29 was a bc 458 this did not look right and while touching the legs with my fingers my modulation increased and the watt meter started too peek up.took out tr29 and replaced with a bc945 and wow modulation now on all mode lsb/usb/am.same probem with another cb cobra 148 my friend wanted fixed.my other email is [email protected] cobra cb radios .

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  • 1,139 Answers

It looks like you had some loose connections in that CB. you may want to also check for other cold solder joints throughout the units and touch them up with some solder. Might I suggest you use a desoldering tool and then just add new solder to the connection.

Posted on Sep 05, 2007

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Have a Magnum 257HP 10 meter radio. While connected to a 50 ohm dummy load, and a power meter, noticed that the USB and LSB would not modulate when a voice input is placed into the microphone. Also, on...


You may have a radio where the AM limiter has been defeated which can cause all kinds of issues. I would first check the mic is wired right and does not have a problem, the radio should have output with a tone to it on sideband--wattage up to over 20 watts on SSB is normal.

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My cobra 142 gtl loses power about two minutes after keying the mic.


hi

it looks like the output stage is going hot (99%)

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Ihave a gargeled recive sound


Check the position of the mode selector switch. You may be receiving a SSB (single side band) transmission that is not on the exact same frequency as you or, your radio is in AM or FM mode. You will need to select either USB or LSB (upper or lower side band) and vary the clarifier knob until the sound becomes intelligible. If the sound does not become clear, try the other side band and repeat varying the clarifier knob.

Conversely, if you are in USB or LSB mode and there is a transmission on AM or FM, it will have the same garbled sound. Try changing the mode to AM and the FM. If it does not become clear, it is likely a SSB transmission and you are not on the exact same frequency of the transmission you are hearing. Vary the clarifier knob until it becomes clear - or change to the other side band if needed and try the clairfier again.

The short story is that you must be in the same mode and on the same exact frequency. When in AM or FM, this is less of a problem as these are much more wide banded signals than SSB signals.

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How to adjust frequency on transmit??? Galaxy


hELLO THERE
hERE IS SOME MODIFICATIONS FOR THIS RADIO
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Unmarked VR in C139..Med Power AM modulation (DX 33HML only) DX 949,DX 959- VR 1....AM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM Squelch Range, VR 6.....SSB Carrier Balance, VR 7....TX Offset, VR 9....RF Meter, VR10...Final Bias, VR12...Driver Bias, VR13...SSB ALC, VR14...AM High Power, VR15...AM Modulation Meter, VR16...AM Modulation, VR17...SSB Power, VR18...AM Low Power, VC1....10.240. DX 2517 and DX 2527-
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1 Answer

SSB ALIGNMENT


You'll need to connect Frequency Counter to C252 & adjust:

USB Frequency: 10.6975Mhz adjust L126 in receive mode
LSB Frequency: 10.6925Mhz adjust L127 in receive mode

May 04, 2008 | Magnum DeltaForce CB Radio

1 Answer

No Modulation!!


Hi,

Most modulation problem could be traced to:
1. mic or the cable and/or the mic connector;
2. AMC (amplitude modulation control) - it's a single transistor that regulates modulation and occasionally has been known to clamped on the mic audio;
3. the AM/SSB switch - spraying with contact cleaner is a temporary remedy; and/or
4. audio amp - however if your receive audio is good, then this does not apply.

Hope this be of initial help/idea. Without a model number, I can't be more specific as to component(s) or PCB location but pls post back for any developments (or lack thereof) or should you need additional information.

Good luck and kindest regards.

Feb 09, 2008 | Uniden PC78ELITE 40-Channels Base CB Radio

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