20 Most Recent Cobra 148 GTL 120-Channels Base CB Radio - Page 5 Questions & Answers

Make sure your boots are switched off and run the radio off a good car battery before you start looking for problems inside the radio. This problem may clear or change characteristics when the supply is changed.

Most units do NOT allow modulation adjustment as any more than 90-100% modulation causes adjacent channel signal "Splatter" therefore is subject to restrictions, hence generally that is locked. Also there really is no reason to have more than 100% modulation..as well ... why? I would suggest a voice/speech "Compressor" would be more suited.

Turner+2 Ham CB Radio Microphone Transistorized SSB Base Station Shark Finturner microphone ' eBay

try another mic or check the mic connectionbernardhttp://www.rylwy.com/

No.

Check first your microphone • check if TX is engaging when PTT is pushed. • check for continuity ( mic and cable )If you have not done these steps,try it first, or borrow other compatible mic for Cobra 148GTLfrom your friends on air.

hiit looks like the output stage is going hot (99%)maby the swr is high end eficiancy is lowusualy on ssb the power is higher than on ambernardhttp://www.rylwy.com/

First is check to see if SSB transmits or not==if it does the AM regulator on side wall of radio is bad.Second with a meter and no power on--test the driver and final for shorts or open.If one is bad replace both.let me know what you find.

Ah! these and the cobra 2000 had the same board and same problems--Some will have no transmit audio (check or sub to make sure microphone not the problem) and others no receive audio.If circuit problem both are caused by a filter cap that opens.Usually this occurs when radio has not been used for a long period of time.If you have a schematic for the radio (mine are all out of reach) you will find in the audio circuit a cap (I think it is 220 uf at 10 volts) right near where the volume is controlled that is bad.The no transmit audio problem is another cap in the mic circuit.I hope this helps you as it is likely your problem--note if the audio output IC was bad no receive or transmit audio.shoot me a question by using the make comment if you need further help.73's

T36- 2sc1969/c1969 Output T37- 2sc496/C496T38- 2sc1306T39- 2sc1973

Bad fuse, dirty power switch contacts, corrosion of same as well. Burned out power filter inductor, Burned out resistor, etc.

The problem with these radios (I have owned 4 of them and also repaired them) is that if they were "tweaked" too high several bad things can happen.

If you have both AM and SSB transmit but it is very low output--suspect either the Driver or Final transistor are bad. You will need to unsolder all three leads (ECB) on each transistor and test them with a ohm meter.

If either is bad----replace both--also note which transistors are in the radio--some people will replace them with "higher" output transistors to get more output.

If the radio had modifications for a carrier control---it would only affect output on AM.

The weak point in this radio if it has been tweaked is the voltage regulator IC located on the right wall of the set next to the audio output IC chip.

Checking voltages will not really tell you very much---Confirm first the actual condition of Driver and Final transistors. Some good advice would be if replacing them restores transmit instantly lower both AM and SSB output either with the controls or by alignment of the driver and final stages of the radio.

The fact that the radio was dimming the meter lights before is a dead giveaway that the radio was pulling maximum voltage from the regulator IC in the radio's power supply.

Something else you may want to try that may or may not confirm this is switch the switch on the back of the radio and connect it to the DC power socket----IF RADIO WORKS THAT WAY-internal power supply is damaged and not the Driver/Final stage.

Let me know what you find.

SD TECH

Howdie gord, The way you descibe having to turn your mic. gain almost completely down, sounds as if some one has already gotten to one of the VR's.. This would also require the standard nylon tuning tools. You can google up the specs for the radio, just google the type & model, being sure to specify "mods" on the end. Like: Cobra 148 gtl mods... There are several hundreds of hits you will get. It sounds to me as if someone went in and turned 1 or more of your Variable Resistors in order to get more audio out of your rig! With a Watt and modulation Meter in line I would concentrate on the AM section of mods. Audio in particular. You should also be able to download the schematics for your rig. It will at least show you in relation to your antenna output symbol, where to find your VR's.. The audio is what I would work on 1st. It will say some thing like adjust VR14 or VR12 ect, to adjust your output audio. There are a Great Number of modifications for that rig. It should be checked by an FCC Certified Technician. But alot of Folk's just dive right in! These models, depending on the PLL Chip, may also be capable of talking "Out of Band", and Uncle Charlie is still very active, along with other HAMS in finding the Offenders. I have to say, that I can not stop you from trying to save a few bucks by making adjustments on your own. Dependable Radio Shops are getting pretty far apart now though.. But really gord, all the answers are on youtube, or google. On youtube, you at least get an idea of what you are looking for to cut the audio back down, and make the rig a little less responsive as far as your mic. gain knob goes! I have several Cobras, all SSB,AM, and a couple with FM. I stick with my Kenwoods and Collins gear though. I do like the 148gtl's alot, but they are not type excepted for HAM use! Good Luck gord, and I Hope I have helped in some small way. I live outside of Atlanta, GA. There are alot of truck stops near by. Truckers will most times tell you who is got a Golden Screwdriver and who to stay away from. I wish you a lot of luck and SEASONS GREETINGS from W4Land! 73 P.S. Since no one has to know Morse Code any more, You could study online for Free at www.qrz.com to prepare for a HAM Ticket! It is Very Easy and Quick to get your Technicians Class now. I have a freind that is a Maritime HAM I need to get ready and try and reach him. He is out of Hong Kong by now, so ya'll have a Great Season. Collin...

hello there firstly you will need to raise your antenna has high as possible and buy a preamplifier this will raise the weak stations and give better signals hope this helps

Does the radio have any rf output? Use a swr/watt meter to check. If if doesn't have any output that would be the cause of the problem.. then its another issues..May need some test equipment to find the fault on that one.You could send it in to us and we can fix it. We do not charge to look at any radio -no bench fees-.. Let me know Ill get you any info that you need.

I believe you will find everything you need here http://www.cbtricks.com/radios/cobra/148gtl_dx/index.htmIf it helps please rate my service as, it appears, i have no rating.Thanks.

More than likely the RF power transitor/module is short circuit. The usual cause is a faulty aerial.

Check the regulator in the mains power supply.

Hi rcstss, I would search youtube for that radio, in searching include the word "Mods", if you feel comfortable opening up the case, make sure you have the proper tools handy. Such as a set of "Plastic Tuneing Tools, also a Watt Meter with SWR, and Modulation on it. Also, a Dummy load for the freguencies that it will cover! You would not like to interfere with your freinds. There are a LOT of Mods for that radio.! Or try and find some shop that you can TRUST! It really sounds like a simple problem to fix, but I'm an Old Ham, and it just second nature to me. And I have more equipment than I really have room for! Good Luck, I bet you will find the answer on youtube though! 73, Collin..

• Locate the MB8719 chip that is right behind the channel selector. Wire a SPST switch from pin 10 to ground and another from pin 11 to pin 12.

• Schematic http://minus.com/my8tfHQMD#1

• Channel Chart

• Position 1: sw1 down, sw2 down
• NORMAL CHANNELS

• Position 2: sw1 up, sw2 down
• 15=26.815 20=26.885 25=26.925 30=26.985(ch3)
• 16=26.835 21=26.895 26=26.945 31=26.995(ch3A)
• 17=26.845 22=26.905 27=26.955 32=27.005(ch4)
• 18=26.855 23=26.935 28=26.965(ch1)
• 19=26.865 24=26.915 29=26.975(ch2)

• Position 3: sw1 up, sw2 up

• 1=27.605 6=27.505 10=27.555 14=27.605
• 2=27.455 7=27.515 11=27.565 16=27.475
• 3=27.465 8=27.535 12=27.585 20=27.525
• 4=27.485 9=27.545 13=27.595 23=27.575
• 5=27.495

• Position 4: sw1 down, sw2 up

• 1=27.605 11=27.725 21=27.855 31=27.955
• 2=27.615 12=27.745 22=27.865 32=27.965
• 3=27.625 13=27.755 23=27.895 33=27.975
• 4=27.645 14=27.765 24=27.875 34=27.985