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Help Identifying Cobra 142 GTL Mods?

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#1
Hello everyone, my first post here. I've been playing with various CB radios for a while but this is the first CB I've ever had that's been modded. Picked up at auction for 10 bucks. I was wondering if anyone could help me identify what has been done to this and what the 5 switches do? Also added some yellow arrows in the pics to show circuits that have been cut (that I noticed) any help is much appreciated! If more pics are needed please let me know!! Thanks in advance!!

Cobra 142 GTL - Album on Imgur
 
Joined
Dec 16, 2013
Messages
341
Location
1158 W. Valley Circle, Ash Fork, AZ 86320-482
#2
The 142 GTL is a very easy rig to modify. Lots of space and easy to disassemble.

It appears that the mod is for extra channels. I have fixed some radios for friends and the modifications they come with are always for extra channels. I sometimes have to back them out to get the unit working again. Some are simple and others more elaborate.

Usually, when all of the switches are in a default position, the radio operates normally. However, with other switch settings, the selections on the channel switch map to a different set of channels. Many of those new channels are not legal CB channels.

The bank of four switches on the rear panel, are wired directly to the programming pins on the MB8719 PLL IC. The MB8719 is a very common PLL chip and is used in many different CB sets. For some detail on modifications using that chip, try going to PLL Frequency Mod Diagrams. Once there, do a search on "8719" and it will take you to a section on that IC.

If you do a google search on "MB8719 pll mods", you will get a bunch of hits on various mods. Here is a link to download a data cheet on the MB8719 PLL IC.

MB8719 Datasheet PDF - ETC

There may be other changes that you have not noticed yet. Like cut traces on the PCB. I hope you know how to read schematics because, to map out exactly what the changes you need to get a copy of the schematic and manual at Cobra 142GTL . Then refer to the mods on the mod sheet listed above, to figure out which one does what.

The single switch on one side is a bit of a puzzle yet, but unless I had the unit in front of me, it would be difficult to figure out. You have a better chance than I do.

Whether the mods are useful or not, is up to you. You might be better off removing them and put the radio back to it's original intent. Watch out for cut traces on the PCB.

Good Luck

Martin - K7MEM
 
Joined
Oct 23, 2016
Messages
326
Location
Clinton Iowa
#3
Hello everyone, my first post here. I've been playing with various CB radios for a while but this is the first CB I've ever had that's been modded. Picked up at auction for 10 bucks. I was wondering if anyone could help me identify what has been done to this and what the 5 switches do? Also added some yellow arrows in the pics to show circuits that have been cut (that I noticed) any help is much appreciated! If more pics are needed please let me know!! Thanks in advance!!

Cobra 142 GTL - Album on Imgur
The radios been modified and now Illegal ! Get rid of it, best option.
 
Joined
Nov 26, 2016
Messages
2
#4
Thank you very much, very helpful information. I'm confident I'll be able to sort it all out!! I'll post an update once I have some progress!!
 
Joined
Dec 24, 2008
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49
Location
Ishpeming,Michigan... A Yooper! "In Da U.P.&q
#5
Looking at the JPEGs, I would recommend removing any glue like material that is located to hold components in steady position. Some of this can be seen in the first pic, it is between the green capacitors. As this material ages it becomes hard and brown also it tends to become conductive causing shorts and false signalling or grounding. Worse yet is that this stuff can etch copper traces!
The lone switch appears to control the power to either the modulation circuit or the AM power itself. This would not be a good mod as it can shorten the life of several components and mainly the finals and driver.
Appears the power supply has a larger capacity filter cap, probably to allow more power to the AM regulator with the mods.

73 poikaa
 
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