Ever seen this one? Cobra 25 LTD

[LeapFrog]

I bought this radio off of eBay I take it it used to be a truckers radio because of the note that was attached to it and some type of fleet number.
Take a look at the picture and let me know you think, I tried googling the component designation numbers Involded in the circuit tweak, I can't find anything about this mod.
[photo="medium"]4102[/photo] R4, R7, And a Diode!??
Thanks
-LeapFrog

 

[w9cll]

What picture?

 

[LeapFrog]

Sorry about that, it is edited in now thanks for taking a look.

-Sam aka "LeapFrog"

 

[LeapFrog]

Better yet can someone help explain what adding a diode at that Junction will do? Is this some type of positive peak expansion or AMC modification?

 

[jon666]

Better yet can someone help explain what adding a diode at that Junction will do? Is this some type of positive peak expansion or AMC modification?

it is a swing mod. or others would call it a npc mod. all it does is make your radio overmodulated. and sound like shit. i know ill get bashed for saying this. but its the truth.

 

[Robb]

Can't see the board; where has the diode been inserted?
Using which resistor in series?

 

[LeapFrog]

Can't see the board; where has the diode been inserted?
Using which resistor in series?

Diode was inserted into one whole for r7, the other end of r7 tied to the diode (banded side i think) and then r4 had one leg lifted and was tied to the solder point where the diode and R7 meet, possibly forming a voltage divider?
I'm not at the house right now but when I get back in front of the radio I will confirm the component destination and the way this diode is currently bodged in.
Thank You.

-Leap

 

[LeapFrog]

The diode used was a standard 1n4148, at least I can read "48" without removing the mod.
The end of R7 (220 ohm) that is farthest from FET1 was lifted from the board & the banded end of the diode was soldered to this end of R7, then the other end of the diode was placed where the leg of R7 used to be.

The end of R4 (220 ohm) that closest to the bezel was lifted out and soldered where the diode and R7 was now meet forming a junction.
The resistor values are original and unchanged.

I am interested at looking at the waveform this mod would produce, or even an REA modulation monitor that would plainly allow me to see what (if anything) this does to the negative/positive peaks.
EDIT: I'm starting to realize this may not even effect the TX circuit!

Looking at the schematic this "mod" would be D25??!
I have two 25 LTD classic radios in front of me, one has this diode the other does not, although I need to look harder i see no silk screen for D25 on either radios!
Both radios use the TA7222AP Audio I.C. & labeled as 25 LTD Classic.
One Is Phillipines & the other China(The one with the bodge)
-Sam aka Leap

 

[LeapFrog]

Something is amiss, upon closer examination of both 25 LTD radios, I found the silkscreening for D25 over by the channel selector/PLL.... With a jumper in place!

I am looking in to this possibly being a circuit update performed on the older 25 LTD's and not a mod?!

According to the schematic this diode is supposed to be where it is..
I am almost certain it is not a factory addition, it just looks too nasty to have left the factory that way imho. I am leaning towards it being an update, on the Philippines radio no such diode bodge is in place.
I am going to comb over the Cobra Tech Bulletin pdf's and see what I find.


If you have a late production Cobra 25 LTD and wouldn't mind taking a snap shot of the area by FET1, you can help me clear some of this fog I am dealing with.
Thanks &
All The Best.
-Sam aka Leap

 

[9C1Driver]

For what it's worth about 15 years ago I had a Delta Force and RCI 2950 that both had the non volted final version of the NPC mod done. Both radio's were tuned on a scope and sounded superb. Another great talker was my Magnum S9 done by Bob's cb. Even with the Top Gun on it sounded great. People can talk all the crap they want about the NPC and the Top Gun, when it's done right it sounds great.

 

[jon666]

For what it's worth about 15 years ago I had a Delta Force and RCI 2950 that both had the non volted final version of the NPC mod done. Both radio's were tuned on a scope and sounded superb. Another great talker was my Magnum S9 done by Bob's cb. Even with the Top Gun on it sounded great. People can talk all the crap they want about the NPC and the Top Gun, when it's done right it sounds great.

see i told you. i would get in trouble for saying its a crap mod. always has been. always will be. to each their own. i would never do it my radios.

 

[LeapFrog]

Hey you guys I appreciate the input I'm trying to keep this on topic I know I posted in the cb mods sub forum.

This thread is not about NPC or PPE I'm just trying to identify what's been done to this Cobra 25, I think I've already figured it out..

-Sam