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Cobra 29 LTD Classic FL2 Filter

RCIGuy

RCIGuy

Active Member
Jan 16, 2023
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Any info on where i could find 1 of these? No success using the cobra parts list number. Receive drops out after transmit (which is not working either, may need a bit of help with it later) and if i tap on it rx will come back, its also has some wobble to it, i suspect the pins are corroded. MFG in philippines 1992, Board #PC-900AD?
This radio is a mess, working on bringing it back from the dead, if it was made in china it would be in the trash can.

29 FILTER.jpg​
 

Those filters come in two basic forms. Three pin and five pin. The filter in the pic is a three-pin. The two extra holes on the left of the filter in that pic have a white screen-printed outline around them. Looks for all the world as if this circuit board is configured to accept either physical package.

The age of easily buying "just one" of an electronic part went away with Radio Shack for the most part. This is a type of part that doesn't fail all that often, so a salvaged part from a junker will most likely work okay.

73
 
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I do have an old uniden pc 77, would that filter work? Found one on the web but they want close to 35 bucks by the time its ships and sales tax, thats 25 bucks more than what i paid for the radio. o_O
 
Apon more investigating i dont believe its the filter. If i key up for a second it loses receive, if i shut the radio off then back on receive is working again.

Edit Replaced c117 no change. TR21 has 7.6v on collector when keyed, 39mv unkeyed.
 
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Replaced TR21, no change, rx will stop working, speaker volume drops to about half to what the volume control is set to.
 
Go Here...

Cobra29 Chrome,L19 and L23 won't work.

Hello gentleman and DXer's,I have a Cobra with issues. When going to get my RX and TX,the frequency just sits and bounces around, and will not adjust. I have my Frequency meter on TP or R61,for my RX and TX. I replaced T20,T7, and a blown diode,D7,the PLL has 10.695, 10.240, and I can see me...
www.worldwidedx.com www.worldwidedx.com

And maybe to help - here...

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

Can you tell me more about the operation of the radio? You said your wife was talking and you couldn't hear her very well or even have any meter movement... That can mean a failed part in the RX chain - or out of tune can...or even a switch in the Wrong Position. Set you radio... You have an...
www.worldwidedx.com www.worldwidedx.com

These two threads dealt with a strange RX problem similar to what you describe, in that post are some other links to other threads that can help you re-tune the radio, and it may possibly fix the problem for you.
 
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Ok, making small steps with progress, had a echo board and variable power mod with wires going all over the place, removed both of them to start with a clean slate. Ive got the no rx after tx problem fixed, a tweak of L22 brought it back. Now to work on to why no tx, no carrier no nothing will check the voltage at the final and go from there.
 
Not sure if you caught this thread - but it helps with Test Points and one of them being R85 - TP4 - about the 3rd page - but there's stuff in those other pages including a quick review tune up - see if any of that can help you.

Need alignment,frequencies points?

Can I get some help here,my son had some fun when I walked away for a moment. He thought it was funny to play turn the cores,on these pots. I posted pictures,can someone give me the low down on how to repair adjust the pots,and where are my frequency check points,as I can align this with minimal...
www.worldwidedx.com www.worldwidedx.com

And to cut to the Chase...
cobra29ifrouting-jpg.35938
 
Last edited:
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Yes ive saved those pics for future references, thank you.

I checked voltage at R70, voltage on both sides.
RX 7.82v on the inside 7.91v on outside facing side of radio
TX 7.49v on the inside 7.88v on outside facing side of radio
 
Ok, it's "on" but awaiting input - so look and retweak L21 that dual can constringent in there...er - coil (y)

R85 has the RF side - but it can also disclose what the Base lead is seeing in DC results.

In TX mode, it also might help to review those pics and "sniff" an RF probe around the paths the RF takes to see if you can localize the condition. To lose RX and then get it back but then lose TX - usually means the TX and RX were not aligned together or straightened out and peaked - I'm referring to when you align the front two wheels of a car - great, you got it going straight as far as the fronts go, but that doesn't mean those rear wheels are tracking that same path.

So if you have that schematic, you know L19 and L18 and L22 but L23 and others from that section - branch off to work RX and TX sides - reheating solder joints would also help you see how the condition of the foil side of the board is. Any foggy results or even what looks to be good, could wind up being a set of holes and a broken lead to a part - so there are more investigations ongoing with this...

1681523137798.png​
 
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Thank you Andy.
Tweaking L21 made no difference, The radio had no tx when i got it. When un-key i can hear a pop sound from the speaker. I will re check the solder side again, maybe i missed something.
 
And double check TR16 your TX Pre Driver

Something sounds too high...
Here's a Voltage Chart for older style Cobra 29's
1681650978465.png


Note that TR16 is not right when it comes to being in TX mode - nor RX
 

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