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Question about Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

142 GTL Good AM Carrier Weak Modulation????

Weak AM modulation at 50% on Palomar PW-5000 meter. SSB has low forward swing with low modulation?? I have checked many voltages in the past and all that I have checked seems normal. Using SAM's Photofact. Re-align transmitter as per Sams with 2-tone audio generator and still low modulation. Replaced Audio IC TA 7222P no change. Any Ideas???

Posted by Mike Autry on

  • Mike Autry Mar 24, 2007

    UPDATE:
    IC4 TA 7222P Voltage Check:
    PIN1 = 13.76v RX / TX = 13.66v
    PIN2 = 7.04v RX / TX = 7.00v SHOULD BE 2.95v !! ??
    PIN3 = 0v
    PIN4 = 0v RX / TX = 0v
    PIN5 = 1.162v RX / TX = 1.162v SHOULD BE 1.95v ??
    PIN6 = 1.158v RX / TX = .8v (Gradual drop in voltage during TX Mic Gain @ Min. like capacitor unloading) SHOULD BE 1.95v
    PIN7&8 = GND
    PIN9 = 7.27v RX / 7.18v TX
    PIN10 = 13.10v RX / 13.00v TX

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2 Answers

Anonymous

Have you checked TR 26 AMC amp, and TR 24 & 25 AMC amps also for SSB TR34 ALC amp. make sure all voltages are right if all checks out try lifting out of the board or cut the collector of TR24 and try it. oop's that slipped out.

Posted on Jul 07, 2007

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squirty whitney

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You may have to scope the finals circuit on the modulation to see if all the "inline" caps are installed correctly... be sure your pc board is grounded in all areas as required by specs in your manual. Make sure there is no bleedover and you are sheilding your crystals from the modulation platform. al

Posted on Apr 30, 2007

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What is Dead Key on a CB Radio?

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I have a Realistic TRC-457.It has very low power and modulation.It is a virgin radio other than someone has replaced the final and driver.I noticet that I cant set the modulation and swr levels on my dosy...

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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 R188..AM/FM Medium Power (DX 33HML only)
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-
Symptom:Buzzing or motorboating sound in either the transmit or receive.
Problem: TR602 is oscillating
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I have an HR 2510 that shows no dead key watts on AM ????

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Audio limiter

tintlady, here is the info you requested;
the AM limiter is R 276

These are the variable adjustments inside,and what they control.
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
VR-10 FINAL BIAS
VR-12 DRIVER BIAS
VR-13 SSB ALC
VR-14 AM HIGH POWER
VR-15 AM MODULATION METER
VR-16 AM MODULATION
VR-17 SSB POWER
VR-18 AM LOW POWER
VC1-10.240 MHz Frequency adjustment

Hope this helps you out, let me know,,Mechanic
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No AM carrier or modulation. SSB transmits good

what cb is it ? it sounds like your am section is not getting powered up when you switch from ssb to am. If i know the model i may have a diagram of it here and suggest a place to start
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