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
