20 Most Recent Cobra 148 GTL 120-Channels Base CB Radio - Page 8 Questions & Answers

Contact the cb shop @ 317 426 9649 They have copies of manuals for pdf type formats..

is this a new radio? if so then the voltage change on the vco/pll will cause a squeak. kindda like a cobra 19dx does. also like the old golden eagle squeal .. all due to the voltage being unstable.. now is it that prob or do you have talkback and its loud/bad grounds causing a squeal. that could be the case too. if you have talk back let me know there's a cure for that. contact us..we can put the talkback just lil outtaphase to stop 99% of the squeals in cobra/uniden chassis radios.

Sounds like you could have a bad soilder joint in the radio. If you hit the top or bottom of the radio does it help? If so its soilder. You match your antenna to your truck not the radio. You might want to recheck it.

You can try this, take the cover off (speaker side) look for TR24 and cut it, one end will do, the remove these, look for R126, and change it to a 2.2k resistor re soldering it in place, makes no difference which way you install it, then look for R124 and replace it with a 2.2k resistor doing the same, then look for L37 and L38 and with a watt meter in line putting a three foot coax jumper in line from radio to watt meter on the lowest scale, tune them for maxim RF output....hope this was helpful...

Try this, plug it all up and turn it on, let it set over night, then try it, after a radio has been put away for a while, the capacitors lose charge...hope this was helpful....

You say your power is good. Have you check the power from inside at the power side.If so check and make sure your voltage regulator legs,three of them, are all good and soildered.Is it blowing fuses?

no AM is alsway an antenna problem, if the antenna connections are ok and the antenna checks good then the radio needs service, but 1st look for defective antenna issues like rusted connection or loose wires.

You can buy an adapter at Radio Shack ....hope this was helpful....

Hello and Welcome to FixYa,
Please do make sure that power is getting to the voltage transformer (For this, you need to check the power cable using a multimeter). There is a possibility that the transformer had gone mal function. To check the working of the transformer, again you need a multimeter to verify its proper working.....
In most cases, if the fuse is intact and working properly, Transformer in the power supply is the bottle neck of the trouble.......

Best Of Luck,

Do RATE the solution, If found Helpful.

Regards...

Requires about 2 hours of labor. All of the frequencies have to be realigned after the modification. Contact dodgem250.com for service and upgrades.

you most likely have a bad knob the pot need to be replaced

the reset button is used to reset the cpu when doing mods.try replacing with momentary press switch.
good luck
ken

Well if they have a Radio Shack it is the place, Corba 148 is a great radio. hope this helps..

Unplug it,and remove the cover. Hook it back up and turn it on. Take a pencil with the eraser end and gently press around where the volume is soldered in the circuit.Wiggle the volume knob,listen if volume change. Sounds like a cold solder joint.Re- solder the joints to volume,or could be a dirty control, if still no volume, turn off and spray inside of volume tuner with contact cleaner. hope this helps..

Pin #1-audio-white,2-shield,3-black,4-Sw com,5-transmit-red .....hope this helps..

Wow, First off, you have a darn good radio there. I had a 148 GTL myself, years ago. I had a Ham Radio Bench Tech max it out for me. ie.
Enabled full coverage from 26-29 MHz, unlocked the clarifier trans./recv. -15Kc to +10Kc from "0" so I could cover the 20Kc jumps on Ch. 3,11,19, and 22..or 23... I think...(It's been awhile..) Peaked the trans. finals to 25W RMS / 30W Peak on SSB and a flat 12W dead key on AM. And I could modulate 120% with a stock mic. (I eventually switched to a K40 Speech Processor.) Add that to a Siltronix 3 Step Variable Linear @ 5 / 10 / 20X Step, with a 30W Max. Rf. Input, coupled to a pair of Avanti Co Phase (center loaded) Hippo's..(1500W max input rating for each one)...Well enough bragging...You brought back memories...Hope I don't get fired by FixYa...
Anyways,
I believe your audio signal is getting lost in, or before, the circuit that changes and mixes your audio signal to the Rf Pre Amp Output signal.
I assume you know electronics, have a oscilliscope, Audio Freq. Gen. and the proper "SAMS FACTS MANUAL" or a comparable circuit block / component diagram with the standard TSD test points data ref. values. If you don't have the above, take it to a shop. Don't take a chance on the hit and miss R&R parts until you get it working.
OK Here we go:
If your PA works, you can eliminate alot of diagnosis time in testing, and block circuit diagnosis too, providing I understand your above statement correctly.
If your words "throws a key to my bench radio" means you have a steady RF Output, and the PA function works properly, Do This: Does the Mic. Modulation register a reading when selected? If so, your audio input amp./mixer circuit is ok. Therefore, the problem has to be between the PA / CB splitter circuit and the Audio / Rf Mix / Conversion circuit, which is the only circuit ( except for a buffering circuit) between there and the Rf. Pre Amp Circuit.
That is where you need to focus your attention and your tests.

Yuo need to set the milliamps on the pre driver,and all finals,or you will quickly burn them up, anytime you replace finals, you have to readjust the milliamps...or a tune-up.....hope this helps you........

This is a classic indication of a lost shield or ground connection in the mic circuitry. Double check these connections for good contact in the mic *and* the plug at the other end of the cable.

Check the grounding and SWR or "match"of the antenna system, too. A poor SWR (greater than 1.5:1 or 2.0:1) can cause the reflection of RF back to the radio. Modifications can increase sensitivity of the mic to this unwanted RF.

At a pinch you can use 5 x LR44 button cells, yes that does add up to 7.5 volts but that's near enough, the 5 cells on top of each other are exactly the same size height and width as the 7 volt battery. I am using them in a "Telex" mike
Gray