Cobra 148gtl No Modulation and...

loosecannon said:

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

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Handy Andy said:

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?
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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.

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loosecannon said:

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

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Handy Andy said:

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...

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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.

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groundwire said:

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.

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groundwire said:

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

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