Cobra 29 LTD Classic NO RX/TX HELP!!!!!!!!!!!!!

[Buzzard78945]

2003 Cobra 29LTD

no meter movement,
no sound at all,
no receive.
no dead key no swing

put it in PA mode plug in external speaker to PA port talk to your self all day long
straight pin audio chip


i found a link on CBTRICKS

https://web.archive.org/web/2015040...gi-bin/database/radio_db.cgi?details=1&key=12

Looks like a good deal so i followed the diagnostic procedure removed and checked all components D19 R124 R98 they were all good... no 5V @ that junction so i swapped PLL with another radio same issue

changed the final... just cause i had an extra

WHERE DO I GO FROM HERE??????

 

[Buzzard78945]

just replaced c112 and i now have 5v at the junction of D19 R124 R98 PLL 7&11

still no Rx/Tx

 

[Handy Andy]

PA works - good - that most of the effort there...

Replacing C112 is the 5V filter cap for the PLL - but that doesn't mean you are out of the woods...

There is a 5V regulator that is a simple resistor divider network that supplies the power to the PLL chip and SOME other functions....

To make the rest of it work, you will need to locate some parts and if you haven't already done so, get a copy of this schematic - it's attached...Cobra_-6 is from Rick Jackson - Euro Radio Co - well worth it to review...

Locate the Regulator - TR23 - because you're going to need to take some time and go over voltages using that PDF Cobra_-6 - and Rick will help guide you thru this better once you are able to locate the parts we'll need to research - find them on that Schematic - for it is your Owners Maintenance Manual for that radio..

I can only do so much - to help for starters, I found you TR23...

​

The JPG version of the Owners manual is also included not as good or clear but we can use it in a jiffy to help you.

 

[Buzzard78945]

PA works - good - that most of the effort there...

Replacing C112 is the 5V filter cap for the PLL - but that doesn't mean you are out of the woods...

There is a 5V regulator that is a simple resistor divider network that supplies the power to the PLL chip and SOME other functions....

To make the rest of it work, you will need to locate some parts and if you haven't already done so, get a copy of this schematic - it's attached...Cobra_-6 is from Rick Jackson - Euro Radio Co - well worth it to review...

Locate the Regulator - TR23 - because you're going to need to take some time and go over voltages using that PDF Cobra_-6 - and Rick will help guide you thru this better once you are able to locate the parts we'll need to research - find them on that Schematic - for it is your Owners Maintenance Manual for that radio..

I can only do so much - to help for starters, I found you TR23...

View attachment 35533​

The JPG version of the Owners manual is also included not as good or clear but we can use it in a jiffy to help you.

i have all the schematics and was in the process of checking components from where the TSB sent me

(CB TRICKS website index)

 

[Buzzard78945]

also i dont understand the schematic from what im looking at on the radio the schematic is not clear to me... i spend a good portion of my day looking at automotive schematics... these are slightly different.

i can find any component under the covers aslo thanks

 

[Buzzard78945]

i have factory service manual on CB TRICKS website... there are alot of voltages on the voltage chart it provides i would like to know where to check voltages next thanks

 

[Buzzard78945]

IC1 Voltages are all correct

 

[Handy Andy]

IC ok - then we look to see TR23 - that Yellow Box

I has 3 legs, in the Manual it is a TO-220 style Hi-gain/High Current Pass Regulator.

A Zener is used on the Base to regulate the output...

So with it oriented in the Photo - with it's back towards you - the output would be the CENTER leg or TAB too...

A Voltage table to the Transistors...​

​

The Block Diagram of the Transistors used in it (the stages where the Radio Processes or Amplifies...)

​

There's more - here's a Pin out Lead Identification for the transistors...may help...

So check the "tab" of TR23...
See if you get 8 Volts,
IF Not - we investigate...​

 

[Buzzard78945]

Sorry I did some more voltage checks and forgot to update

TR23 has proper voltages

 

[Handy Andy]

So, no Green RX light yet?

Check to make sure CB/PA (we know you say PA works) but does it switch back?

You would have channel display, RF gain control, even Squelch - you'd be able to turn the front knobs and hear either static from the scrapings or something of a hiss...

The "green" light would be from power from the REGULATOR TR23 - so if those voltages are ok, then the wiring harness's to the front panel - need to be checked

What is the inside condition of the radio like?

• - 2003 is pretty old, nearly 17 years - so it may have problems more related to age of the parts than a tune up.
• There may have been a modification - or a catastrophic failure - blowing traces...
• But a tune up may help us get a better understanding of the problems you're having.

As far as the "Green light" it would work no matter the condition of the PLL being in lock or not. You just can't hear anything or TX the radio - so no RED light but you'd still have Green.

If the PLL was not locked on a channel you have no audio - but you would still have a green light.

CB/PA When you key up the radio - and you don't have a PLL lock - you'd have a Green light, but it would go off, not turn RED - it just goes dark - PLL out of Lock. It acts like the Squelch is on all the time.

 

[Handy Andy]

Can you hear the radio "thunk" thru the speaker when you turn on the power?

 

[Robalo]

o no you going make me check my 29 ltd

 

[Buzzard78945]

I’m assuming TR21 is working there is switch indication @ RX/TX LED indicator on front of radio

 

[Buzzard78945]

So, no Green RX light yet?

Check to make sure CB/PA (we know you say PA works) but does it switch back?

You would have channel display, RF gain control, even Squelch - you'd be able to turn the front knobs and hear either static from the scrapings or something of a hiss...

The "green" light would be from power from the REGULATOR TR23 - so if those voltages are ok, then the wiring harness's to the front panel - need to be checked

What is the inside condition of the radio like?

• - 2003 is pretty old, nearly 17 years - so it may have problems more related to age of the parts than a tune up.
• There may have been a modification - or a catastrophic failure - blowing traces...
• But a tune up may help us get a better understanding of the problems you're having.

As far as the "Green light" it would work no matter the condition of the PLL being in lock or not. You just can't hear anything or TX the radio - so no RED light but you'd still have Green.

If the PLL was not locked on a channel you have no audio - but you would still have a green light.

CB/PA When you key up the radio - and you don't have a PLL lock - you'd have a Green light, but it would go off, not turn RED - it just goes dark - PLL out of Lock. It acts like the Squelch is on all the time.

this radio is spotless on the inside and out looks brand new... no noise at all from speaker no matter what( even if you touch resistor to pa and speaker port on back of radio as if your temporarily adding talk back)

speaker is good ohms out perfect
8 ohm if I remember correctly

like I have said IC1 PLL has all correct voltages during RX and TX

 

[Buzzard78945]

this radio is spotless on the inside and out looks brand new... no noise at all from speaker no matter what( even if you touch resistor to pa and speaker port on back of radio as if your temporarily adding talk back)

speaker is good ohms out perfect
8 ohm if I remember correctly

like I have said IC1 PLL has all correct voltages during RX and TX

Also I’ll reiterate
You can plug aux speaker in PA port, and switch radio to PA mode you can talk to your self all day long...

Switch it back from PA mode and nothing no static squelch all the way down gain all the way up