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144inBama

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Apr 22, 2020
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Newest update::: so different mics didn’t change a thing. So still mid sentence radio goes silent and needle goes to left however my friends still here my transmission. And yes does it with amp on or off. Some days are worse then others.I believe it’s just old school talk back trucker mod . Please help? Any ideas?
I'm going with a bad solder joint then. If you're still transmitting fine and only your TB and needle are failing, it sounds like you are losing a connection somewhere. Time for the magnifying glass and a good light....IMO anyway. You can also check the values of the TB circuit components to make sure they're in tolerance.

Screenshot 2021-09-12 050108.png
 
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Ziploc

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Mar 19, 2016
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I just read back thru it 3 times and have yet to see anywhere you posted that it's a comp cobra 29. (maybe I'm going blind) if it was posted I apologize.
Yeah I didn’t
I'm going with a bad solder joint then. If you're still transmitting fine and only your TB and needle are failing, it sounds like you are losing a connection somewhere. Time for the magnifying glass and a good light....IMO anyway. You can also check the values of the TB circuit components to make sure they're in tolerance.

View attachment 46986
Thanks
 
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Ziploc

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Mar 19, 2016
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Keys up.

Gives you power for a moment, then goes dead.

Bad D8?

Intermittent bipolar final transistor?

Driver transistors can fail, but far less often than finals.

Not gonna get many questions answered about what's shutting down without a few measurements.

73
It’s still is transmitting I lose needle and sound of talk back mid sentence
 

144inBama

Sr. Member
Apr 22, 2020
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So still mid sentence radio goes silent and needle goes to left

If you just hold a dead key for a few seconds then speak, does it still cut out in the same time frame? Is it shorter, longer? It's possibly a bad/weak cap in the circuit. When you modulate the cap can't keep up so it goes open and you lose everything, then when you unkey it allows it to cool and charge....just spit balling here. C76 and C52 are the two I "think" I'd look at.
 
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Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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I'm thinking D21 by Main Regulator - communication from TR21 is lost so it doesn't stay keyed up...

You lose Audio from the loss of speaker return (you're in TX)

upload_2021-9-12_9-54-26.png

And lack of communication may relate to R101 2.2ohm resistor to PTT swtich.
Pin 3 on the MIC.
upload_2021-9-12_9-56-59.png
You haven't answered my other question ...

Do you get a TX light?
 
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Ziploc

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I'm thinking D21 by Main Regulator - communication from TR21 is lost so it doesn't stay keyed up...

You lose Audio from the loss of speaker return (you're in TX)

View attachment 46987

And lack of communication may relate to R101 2.2ohm resistor to PTT swtich.
Pin 3 on the MIC.
View attachment 46988
You haven't answered my other question ...

Do you get a TX light?
Tx light is on yes. It happens whenever it wants . I lose talk back sound needle dies however my people still hear everything I’m saying on the other end. Tried different mics amp on or off same
 

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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Talkback eh?

The mods done to make the Talkback work, is that effort.

IF you're getting out signal and the needle dies?

Something in the rework is not holding up to your expectations...let alone needs...

Then - by your word...

Tx light is on yes. It happens whenever it wants . I lose talk back sound needle dies however my people still hear everything I’m saying on the other end. Tried different mics amp on or off same

This isn't the radio , it's the interface layer between the radio and all your accessories Talkback, the Amp keying circuit - I would suspect being the problem - a simple power cap holding the charge, that when you start to "chat" it drains off - but because of the TX and what appears to be the radio itself seems ok then - your techs work to give you talkback and any external controls thru that work, it seems to be the source of this problem.

A simple relay and cap circuit can do this - if you replaced the relay with one that didn't wire up right or has a different ohmic coil impedance/resistance (coil ohm or draw rating) can also do this for the loose wiring or socket, or relay itself - everything done to "chat" with talkback on and relay interface is suspect right now.
 
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Ziploc

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Talkback eh?

The mods done to make the Talkback work, is that effort.

IF you're getting out signal and the needle dies?

Something in the rework is not holding up to your expectations...let alone needs...

Then - by your word...



This isn't the radio , it's the interface layer between the radio and all your accessories Talkback, the Amp keying circuit - I would suspect being the problem - a simple power cap holding the charge, that when you start to "chat" it drains off - but because of the TX and what appears to be the radio itself seems ok then - your techs work to give you talkback and any external controls thru that work, it seems to be the source of this problem.

A simple relay and cap circuit can do this - if you replaced the relay with one that didn't wire up right or has a different ohmic coil impedance/resistance (coil ohm or draw rating) can also do this for the loose wiring or socket, or relay itself - everything done to "chat" with talkback on and relay interface is suspect right now.
I’ll let y’all know more tomorrow. I turned off the TB it’s ran to the cb/pa switch and hasn’t done it yet. Might just be coincidence, I’ll let you know ratchet jawing this week
 
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Shadetree Mechanic

808 On The North Side of Dover
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You loose indication of modulation, but everyone still hears you?


Wow, that certainly puts a nail in "you are the common denominator of all your problems". Yeah that's got to be a cap taking a dump. In my humble opinion of course. That is a problem that I have not read about yet, as I have read about a lot of problems and the fixes in my short time here. Interested in what the fix is.
 
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Ziploc

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Mar 19, 2016
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You loose indication of modulation, but everyone still hears you?


Wow, that certainly puts a nail in "you are the common denominator of all your problems". Yeah that's got to be a cap taking a dump. In my humble opinion of course. That is a problem that I have not read about yet, as I have read about a lot of problems and the fixes in my short time here. Interested in what the fix is.
Dustin will know
 
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