[arm-allstar] YET, YET, Another Cheap USB FOB Mod

Kevin Custer kuggie at kuggie.com
Tue Nov 18 09:17:57 EST 2014

In the grand scheme of things, if a person has the ability to add wires 
to the CM108/CM119, removing the audio connectors is a piece of cake.

Besides, all of the better modifications tell you to cut the jacks off 
the board, and then do the clean-up.  Some modifications require the 
jacks to be removed, so in those instances it is a necessity.

Bottom line - cut the bands or pins with a good pair of cutters first so 
the jack falls off, then minimal heat is required to remove the 
remaining stuff.  Same goes with the USB plug in those mods which 
require it.

A bigger problem is those modifications that do NOT instruct the builder 
to remove the MIC bias resistor.  Many radios with DATA or discriminator 
audio outputs have a fairly high output impedance. If you don't remove 
the bias resistor (commonly around 1k) you can severely load the 
discriminator and the radio won't work correctly.  Removing the resistor 
accomplishes two things.  First, it removes the voltage on the MIC input 
lead and eliminates the need for a coupling capacitor.  Second, it 
raises the input impedance so loading of the discriminator doesn't 
happen.  Sure, on those installs that use speaker audio (yuck) for 
driving the FOB, there are no loading effects, but why buy a coupling 
capacitor when one component can be de-soldered or otherwise removed?  
You aren't saving this component, so you could care less if it gets 
damaged or lost in removal.


On 11/17/2014 11:14 PM, Doug Crompton wrote:
>  My only concern is that for the average person absolute minimum 
> modification of the FOB would be the best avenue. It is so easy to 
> damage and taking out the audio connectors is just not necessary 
> although so many of the mods seem to think it is.

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