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Cobra 29 WX NW ST ..... NO RX/TX

Buzzard78945

Buzzard78945

Active Member
Feb 8, 2020
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OK im very new to CB radios i have some electrical experience, i can solder and diagnose if i have the proper information i can understand.

This radio will not send or receive, no sound at all.
I tried new mic, external speakers, no out put on PA mode at the rear port

Inside the box...
I have a IC4 getting very hot while radio just turned on... i replaced with known good one same issue.
must be an effect not the cause of the issue

no cold solder joints or issues with the board it looks brand new any help would be appreciated THANKS!
 

Ok, before you cook it...

Do you know how old that radio is? 29's been around for years, but older the radio chassis of that brand is, the more likely they have old parts that are known to fail.

Johnny5.jpg​

So what kind of IC4 do you have?

The TDA7222AP - the row of pins one, or the Youda chip with also 10 pins but a lot of them aren't used...or...do you have the TDA2003/2005 one with 5 pins pyramid?

There are several reasons for that IC to be heating up

One of them being, the Electrolytic capacitors.

Cobra29IC4.jpg

Youda 1022 chip schematic...
YD-1022IC4C29.jpg


So...
GotAboardnumber.jpg
We need a little help here to help you...​
 
Handy Andy said:
Ok, before you cook it...

Do you know how old that radio is? 29's been around for years, but older the radio chassis of that brand is, the more likely they have old parts that are known to fail.


So what kind of IC4 do you have?

The TDA7222AP - the row of pins one, or the Youda chip with also 10 pins but a lot of them aren't used...or...do you have the TDA2003/2005 one with 5 pins pyramid?

There are several reasons for that IC to be heating up

One of them being, the Electrolytic capacitors.

View attachment 34353

Youda 1022 chip schematic...
View attachment 34355


So...
View attachment 34356
We need a little help here to help you...​
Click to expand...


I have the 3/2 pin not straight
 
Handy Andy said:
Ok, before you cook it...

Do you know how old that radio is? 29's been around for years, but older the radio chassis of that brand is, the more likely they have old parts that are known to fail.





So what kind of IC4 do you have?

The TDA7222AP - the row of pins one, or the Youda chip with also 10 pins but a lot of them aren't used...or...do you have the TDA2003/2005 one with 5 pins pyramid?

There are several reasons for that IC to be heating up

One of them being, the Electrolytic capacitors.

View attachment 34353

Youda 1022 chip schematic...
View attachment 34355


So...
View attachment 34356
We need a little help here to help you...​
Click to expand...

Oooohhhhh I get the triangle now sorry I’m used to automotive schematics ‍♂️
 
Ok! Cobra 29 of 2011 - with a possible TDA2005 chip so you have a more modern one.

We-e-ell - to continue, when you get some tools in to check further... we will be here to help guide you.

Usually when the thing won't TX or RX - the power supply feed section, the one that helps regulate 8 volts to power different sections - if that went bad, all you get is the meter light and maybe a channel display but otherwise dead. PA doesn't mean it will work either - as you found out.

So there will be more work ahead of you - but if you take your time and work in small steps you'll do fine and we may have it back up and running pretty soon.

But for now, that IC4 chip getting hot has me concerned as to why it's heating up and it usually means that the longer it's powered up and not all the parts on the side panels - like your IC4 are NOT assembled properly - may cause an even bigger fail - so refer to this as I'm talking about someone previously working on your radio that left it for later to fix after an initial attempt - you have to probably remove IC 4 from the board so you don't cook or ruin it, or the power supply, or the Modulation transformer from possible shorts or otherwise a catastrophic failure that has happened or WILL HAPPEN if something is not done...
 
Handy Andy said:
Ok! Cobra 29 of 2011 - with a possible TDA2005 chip so you have a more modern one.

We-e-ell - to continue, when you get some tools in to check further... we will be here to help guide you.

Usually when the thing won't TX or RX - the power supply feed section, the one that helps regulate 8 volts to power different sections - if that went bad, all you get is the meter light and maybe a channel display but otherwise dead. PA doesn't mean it will work either - as you found out.

So there will be more work ahead of you - but if you take your time and work in small steps you'll do fine and we may have it back up and running pretty soon.

But for now, that IC4 chip getting hot has me concerned as to why it's heating up and it usually means that the longer it's powered up and not all the parts on the side panels - like your IC4 are NOT assembled properly - may cause an even bigger fail - so refer to this as I'm talking about someone previously working on your radio that left it for later to fix after an initial attempt - you have to probably remove IC 4 from the board so you don't cook or ruin it, or the power supply, or the Modulation transformer from possible shorts or otherwise a catastrophic failure that has happened or WILL HAPPEN if something is not done...
Click to expand...

I have a meter on the way...

When I have it installed I’ll get with you on more info

so your saying remove ic4 then proceed with diagnosing issue... ( I understand keep letting it get hot and it will damage something )

what do I check after removing?

when I was looking at it I pulled a schematic and got voltages at the chip all 5 legs wrote them down letting it cool 5 to 10 min in between having it on for 30 seconds max

I’ll provide voltages soon, I was trying to trace back from chip to each component and check components as I could I was having some trouble understand schematic that I had
 
It’s a fairly new radio in comparison to other golden oldies I have, and I’d like to fix it if at all possible night watch still works
 
You have to figure out why IC4 is overheating...

You need to know what IC 4 does - and how it works...

The Audio Chip (IC4) uses a capacitor to send audio power into a tap on a coil - the Modulation transformer - or some call it Reactance Modulator.

If the capacitor is bad, or shorted, it will send power back into the Audio Amp chip and the chip is going to try and dissipate that power.

So I'd remove the large cap right next to the Modulation Transformer first to see if the chip will cool down - then if it does, the cap was bad.

upload_2020-2-22_21-42-59.png

If is doesn't then the IC4 may have to be pulled as well to keep it from damaging any other sections from it - it isn't often but it is possible that when they fail their internal regulator can't dissipate power to even keep voltages properly set inside - so it heats up and acts like a dead short to the system - pulling power until it pops a trace like a fuse or it completes it's self-destruct sequence.

Another section you'll need to look into?

Power regulator that supplies 8 votls to many parts of the board requiring a consistent and steady safe regulation voltage to operate - that you'll also need to check..
upload_2020-2-22_21-41-16.png

You may be in over your head, and this will be a challenge so as I work with you I will need to know what you see and have in front of you - pictures do help - so help me as I try to help you...
 
Handy Andy said:
You have to figure out why IC4 is overheating...

You need to know what IC 4 does - and how it works...

The Audio Chip (IC4) uses a capacitor to send audio power into a tap on a coil - the Modulation transformer - or some call it Reactance Modulator.

If the capacitor is bad, or shorted, it will send power back into the Audio Amp chip and the chip is going to try and dissipate that power.

So I'd remove the large cap right next to the Modulation Transformer first to see if the chip will cool down - then if it does, the cap was bad.

View attachment 34580

If is doesn't then the IC4 may have to be pulled as well to keep it from damaging any other sections from it - it isn't often but it is possible that when they fail their internal regulator can't dissipate power to even keep voltages properly set inside - so it heats up and acts like a dead short to the system - pulling power until it pops a trace like a fuse or it completes it's self-destruct sequence.

Another section you'll need to look into?

Power regulator that supplies 8 votls to many parts of the board requiring a consistent and steady safe regulation voltage to operate - that you'll also need to check..
View attachment 34578

You may be in over your head, and this will be a challenge so as I work with you I will need to know what you see and have in front of you - pictures do help - so help me as I try to help you...
Click to expand...


Thanks a bunch!!! When I get the meter in the mail I’ll get installed and begin the diagnostic trail with you!!! Thanks again!
 

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