Cobra 148gtl No Modulation and...

[Gunner357]

did you say you adjusted VR5 for the modulation?

if that's the case, then what you adjusted was the frequency the radio transmits on when you key up the radio.
unless the clarifier has been unlocked in which case it would do nothing at all.

the VR to adjust for modulation in the 148gtl is VR7, located in front of the big soda can looking capacitor toward the rear right.

this could have just been a typo, but i thought it would be worth a check.

weak modulation is a different problem than no modulation.

if the radio seems to receive ok and you can hear voices coming in through the speaker at a normal volume then your audio IC is probably fine.

if you are going to tune L38 over near the final, do that while putting a tone or your voice into the mic. don't just tune it for max deadkey.

also be sure that the power source you have the radio connected to can deliver at least 3 amps continuous.
your radio never draws anywhere near the same current while receiving that it does while transmitting audio.

if your radio can deadkey 4 watts, you final and driver are fine.
you might try some contact cleaner in the DYNAMIKE potentiometer and work it back and forth, as your mic audio passes right through it, and if it seems hard to turn there could be a bunch of gook in there.
LC

yes it is a typo sorry ....... Now I dont know what I did but its modulating i was testing the voltages on the IC's thought the IC6 was strange well its 2 am here now and I cant test very loud but I said audio real soft ant the radios meter moved so I hook my ext modulation meter up and the ext speaker and the pa was working so I went ahead and tried more audios and me saying softly I was getting 100% no clue what i did......now I saw somewhere about if the radio sat un used for years you need to leave the radio on for a few hours to recharged caps and such dont know if thats true but my radio been on continuously for 3 hours ,someone else said they have the same radio and left it on and the modulation started working again after setting for years a new un used OLD 148gtl well im going to leave the radio on all night see what happens. I post the results

 

[Gunner357]

So after leaving it on all night I picked the mic up whistled in it hey modulation ....so i wanted to adjust the MOD with VR7 now no modulation I give up.....

 

[Handy Andy]

Wow, this can turn into a disaster real quick...

Ok, now you're heading in the right direction - leave it on for an hour to help stabilize the radio since you do not know of how it was treated by original owner or if it ever had one.

The age of the board is the concern. And what is classic about these symptoms is how Manufacturers like Ranger and Maxon amongst others from the foreign imports, got chided for poor soldering and below-part components and crappy assembly errors.

This began back in the 90's your radio fits these profiles to a tee, including such symptoms as poor soldering and lifted traces.

Ok, so - You got a Lemon, let's make Lemonade, but in the meantime - slow down and start doing simple steps approach, like knowing you have PA - that's great, means the Mic and Volume seem to work, you just don't have Modulation.

• But..

HOW ARE YOU CHECKNIG THE PA?
I need more info here, are you simply listening or did you have a chance to put the mic thru it's paces and work the PA side where you can hear your own voice thru the PA speaker? This helps us in trying find the trouble spots in the audio path. The more effort you try in discerning how you sound in the audio you hear coming back at you from the extension speaker -now PA speaker, can help us determine your radios condition.

It's not just - that you can hear audio, it's the ability to use the mic for a purpose means that one the base function's of the radio is working.

• Do you have a Receive?

You can hear that thru the Speaker, but how well is this receive working?
​

Can you read a schematic, can you locate these parts on the board? This is where I see there's some issues with how you can try and repair this radio.

It takes patience, I'm working right along side you in my own radios - I guess I'll have to take out that old Cobra from Uniden days and help you, but I don't have the EXACT radio in which to GUIDE you to these locations I believe are causing your trouble.

 

[loosecannon]

honestly right now i think you don't have a radio problem, you have an intermittent problem and need to start poking, prodding, and pressing in strategic spots and see of you can't recreate the problem consistently.

many a tech has run themselves ragged looking for a problem on a circuit board that doesn't exist.

I know you said you tried different mics, but there is always a common denominator.
go back and try things again, all the while trying to physically manipulate the radio.
if nothing changes, then at least you've eliminated a possibility.
never assume it "can't be that".
LC

 

[Gunner357]

Wow, this can turn into a disaster real quick...

Ok, now you're heading in the right direction - leave it on for an hour to help stabilize the radio since you do not know of how it was treated by original owner or if it ever had one.

The age of the board is the concern. And what is classic about these symptoms is how Manufacturers like Ranger and Maxon amongst others from the foreign imports, got chided for poor soldering and below-part components and crappy assembly errors.

This began back in the 90's your radio fits these profiles to a tee, including such symptoms as poor soldering and lifted traces.

Ok, so - You got a Lemon, let's make Lemonade, but in the meantime - slow down and start doing simple steps approach, like knowing you have PA - that's great, means the Mic and Volume seem to work, you just don't have Modulation.

• But..

HOW ARE YOU CHECKNIG THE PA?
I need more info here, are you simply listening or did you have a chance to put the mic thru it's paces and work the PA side where you can hear your own voice thru the PA speaker? This helps us in trying find the trouble spots in the audio path. The more effort you try in discerning how you sound in the audio you hear coming back at you from the extension speaker -now PA speaker, can help us determine your radios condition.

It's not just - that you can hear audio, it's the ability to use the mic for a purpose means that one the base function's of the radio is working.

• Do you have a Receive?

You can hear that thru the Speaker, but how well is this receive working?
​

Can you read a schematic, can you locate these parts on the board? This is where I see there's some issues with how you can try and repair this radio.

It takes patience, I'm working right along side you in my own radios - I guess I'll have to take out that old Cobra from Uniden days and help you, but I don't have the EXACT radio in which to GUIDE you to these locations I believe are causing your trouble.

ok last night I had it on PA when I noticed modulation so I went from there with the PA YES I could hear my voice, YES I do have receive, and confirmed with another that the cobra was on the same frequency. However again when I got up this Am I had it on CB and whistled and it had modulation , so I got my MOD meter so I could adjust VR7 now no modulation none ON AM,SSB,or the PA I cannot find R128 I took a picture and according to CB tricks Schematic it should be there NADDA.... SO Im assuming this radio being a early model 1996 that CB tricks Schematic is not for my CB

 

[Gunner357]

honestly right now i think you don't have a radio problem, you have an intermittent problem and need to start poking, prodding, and pressing in strategic spots and see of you can't recreate the problem consistently.

many a tech has run themselves ragged looking for a problem on a circuit board that doesn't exist.

I know you said you tried different mics, but there is always a common denominator.
go back and try things again, all the while trying to physically manipulate the radio.
if nothing changes, then at least you've eliminated a possibility.
never assume it "can't be that".
LC

well with respect to the Mic I have an adapter to let it go from a 6 pin to 4 I tried it on my Cobra 29 and it worked fine.... Also I tried (2) 636l and a Ranger Mic no go...... I am starting to wonder if its the MIC connector Circuit board on the radio?

 

[Gunner357]

I verified the cobra power mic again on another radio and on level 2 I can whisper and get 100%..... now I hooked power mic back up to the 148gtl turn pa on I can hear my voice keyed it 3 or 4 times then it went dead again

 

[Handy Andy]

I verified the cobra power mic again on another radio and on level 2 I can whisper and get 100%..... now I hooked power mic back up to the 148gtl turn pa on I can hear my voice keyed it 3 or 4 times then it went dead again

Ok, I'm with @loosecannon on this one...

The pics you have supplied us of the condition of the board and it's soldering is what were trying to address. It's compounded by age.

We started down the path of poor soldering and you found several areas to fix - but then it quits..and you give up...

Well, to me, you haven't given up, at least you keep going back to it - and thanks from all of us ahead of time - for not slamming it into a wall when you get tired of it.

For What It's Worth...you're just learning what it is like to be a technician and fix things that other people tell you it's broken and you have to sort out what works and what doesn't and how to get the two sections to work as one unit again.

Welcome to Tech 101 - learning how to be patient - with the patient.

It's not uncommon to give a device it's space to warm up and it'll work for only moments - but it works well for that time, until it stops and even though you were gingerly coddling and keeping it steady - it still fails - so why?

Well, most of the time - it's vibration and simple things like thermal expansion and contraction that really shows up here...and it sounds like this is the very thing you're recreating every time. A thermal problem that relates back to the age and time of the assembly - poor assembly as well as too cold of soldering done to these parts, and in it's moments of working - it's doomed to fail because of the assembly itself - not the parts.

It's just not put together very well.

Which, in perspective - when you look at it, makes this a classic tale unfolding before our very keyboards... that is what made everyone else want to run away from, back in the 90's until someone at the manufacturer said, either we fix this problem or we lose our jobs.

Funny - now you know why they had so many different places of Origin - one contacted company after another made promises they couldn't keep.

Cobra went out searching the jungles to find another shop to do their dirty work...with the debris of half working radios built, to be left behind - in the former shops efforts of taking a loss, and littering the shelves of truck stops and old CB stores until they get cleaned out, to be thrown into a landfill, or ULP! to be picked over - in a Garage Sale...Just think, in that darkeness of the Shipping Containers these things sat in until they finally saw the Fluorescent light of "Day" at a 24-hour Truck Stop...

Can make you Sea sick...

​

Some radios are lucky enough to find owners like you willing to put the time in to make them work again...

The problem is, the companies never took back their POS product and made it right - instead they wrote it off as a loss and left it in stock for others to uncover from an archeological dig like a Garage sale often becomes and they satiate and try to make it work only to become frustrated.

Hey! We all are over this - we are PASSIONATE about what we do - it's what were trying to convey to all whom read this.

 

[Gunner357]

Ok, I'm with @loosecannon on this one...

The pics you have supplied us of the condition of the board and it's soldering is what were trying to address. It's compounded by age.

We started down the path of poor soldering and you found several areas to fix - but then it quits..and you give up...

Well, to me, you haven't given up, at least you keep going back to it - and thanks from all of us ahead of time - for not slamming it into a wall when you get tired of it.

For What It's Worth...you're just learning what it is like to be a technician and fix things that other people tell you it's broken and you have to sort out what works and what doesn't and how to get the two sections to work as one unit again.

Welcome to Tech 101 - learning how to be patient - with the patient.

It's not uncommon to give a device it's space to warm up and it'll work for only moments - but it works well for that time, until it stops and even though you were gingerly coddling and keeping it steady - it still fails - so why?

Well, most of the time - it's vibration and simple things like thermal expansion and contraction that really shows up here...and it sounds like this is the very thing you're recreating every time. A thermal problem that relates back to the age and time of the assembly - poor assembly as well as too cold of soldering done to these parts, and in it's moments of working - it's doomed to fail because of the assembly itself - not the parts.

It's just not put together very well.

Which, in perspective - when you look at it, makes this a classic tale unfolding before our very keyboards... that is what made everyone else want to run away from, back in the 90's until someone at the manufacturer said, either we fix this problem or we lose our jobs.

Funny - now you know why they had so many different places of Origin - one contacted company after another made promises they couldn't keep.

Cobra went out searching the jungles to find another shop to do their dirty work...with the debris of half working radios built, to be left behind - in the former shops efforts of taking a loss, and littering the shelves of truck stops and old CB stores until they get cleaned out, to be thrown into a landfill, or ULP! to be picked over - in a Garage Sale...Just think, in that darkeness of the Shipping Containers these things sat in until they finally saw the Fluorescent light of "Day" at a 24-hour Truck Stop...

Can make you Sea sick...

​

Some radios are lucky enough to find owners like you willing to put the time in to make them work again...

The problem is, the companies never took back their POS product and made it right - instead they wrote it off as a loss and left it in stock for others to uncover from an archeological dig like a Garage sale often becomes and they satiate and try to make it work only to become frustrated.

Hey! We all are over this - we are PASSIONATE about what we do - it's what were trying to convey to all whom read this.

well I'm not giving up!!~ I found another lifted foil that held a cap i re-soldered haven't tested yet Im going to go over the board again and solder what looks bad..... however i would still like to try lifting that r128 if anyone can tell me where it is I looked at the schematics every is there but the r128 on my radio

 

[groundwire]

Im gonna leave mine on for hours and then see if it has audio like yours did and stops flashing back and forth from tx to rx.

 

[Gunner357]

Im gonna leave mine on for hours and then see if it has audio like yours did and stops flashing back and forth from tx to rx.

your not going to believe this i started messing with the vr10 and vr 7 now I have Modulation if I max the VR10 to 8w DK modulation is great if I set it back to 4w DK I have modulation but cant calibrate my modulation meter,,,,,

 

[Gunner357]

I set it to 5w dk and the Power mic level 4 and its creaming.... Ill need to back down VR7

 

[Gunner357]

I just took a drive and call my GF she was on this Cobra and power mic level 2 loud and clear level 10 loud a little distortion at this point Im leaving it going to button it up..... thanks for the help is till wanna know where r128 is so shout out if you can find it if this board even has a r 128

 

[groundwire]

yup i can receive and when I key I can DK up to 8w its set at 5 right now But no modulation no swing on the radio meter or the ext meter ....

what is the production date on yours?

I was totally wrong. Just looked at the radio and its a august 1994 malaysia.

 

[Gunner357]

I was totally wrong. Just looked at the radio and its a august 1994 malaysia.

yeah mines a 96 Malaysia i assume the same fixins