first download the factory service manual here:
http://www.cbtricks.com/radios/cobra/2000gtl/graphics/cobra_2000gtl_sm.pdf
on page 49 you will find a picture of the mic connector board.
if you blow up the pic to about 300% you can see that each pin connects to a PC board trace, and the wires are soldered to the other ends of these traces.
the reason the wires are not soldered directly to the pins is to accommodate some capacitors and ferrite chokes that help eliminate mic feedback, AKA "squeal".
we will use the diagram in the service manual as our reference as far as which pin is which, but drawing a few diagrams of your own will prove helpful.
looking at the diagram, you will notice that the pins are oriented in the shape of a "C".
starting at the bottom of the "C", the first pin is pin 1, which is the AUDIO pin. Follow the trace that connects to that pin and the wire you find will be the AUDIO wire that goes to the main PC board.
do the same thing to find the wire that corresponds to each pin.
Following the "C" in a clockwise direction, the next pin will be pin 2 which will be the SHIELD for the AUDIO wire.
next around will be pin 3 which is the RECEIVE pin.
next will be pin 4, the switched ground for RX to TX switching. (DO NOT use this pin for grounding anything on your echo board. only use pin 2)
finally at the top of the "C" will be pin 5 which is the TRANSMIT pin.
this will be the pin they refer to as PTT (push to talk) in your echo board instructions.
ok, you will notice that the wires connected to pins 1 and 2 are one shielded cable with the center wire going to pin 1 AUDIO, and the shield going to pin 2 SHIELD/GROUND.
you may find it easier to work on this board by unscrewing the ring connector from the front of the radio allowing you to move the board around to where things are easier to get to. a word of caution about this though.
trying to grip that ring connector with a pair of pliers will almost always cause it to slip and you will scratch the face of your precious 2000GTL.
you need a tool that will it in the little notches in the connector.
you can make your own, but thats up to you and your mechanical ability.
you may just find it easier to leave the board where it is.
if you heat the solder trace where the wire is connected, you should be able to gently pull the wire out of the hole its in. just be careful and watch your heat.
once you get the AUDIO and SHIELD wires unsoldered from the mic connector board, you can just solder the wires from the echo board right to the solder blob on the back of the board. no need to try to put it through the hole.
again, its your radio and its up to you how you want to do it.
just take your time and do it neatly.
try to mount your echo board somewhat close to the mic board so you can keep the black negative wire from the echo board as short as possible. (about 6" or so)
this will help with squeal from the echo board.
better to add some length to the positive wire than keep the negative wire long.
as for where to draw the power for the echo board from, i like to use the positive terminal of C172. this is a big 1000uF electrolytic capacitor in the rear right portion of the main PC board.
if you look at page 18 of the service manual you downloaded, and find the black box with the number "1" in it, you will see that it is a 13.8 volt source, and the arrow will show you which trace is the positive.
to avoid making a mistake about which trace it is, as it can be hard to see; confirm it by using a voltmeter on the DC setting and make sure you measure about 13.8 volts on the trace with the radio on.
put the negative lead of the meter on any of the metal tuning cans on the PC board as they are all connected to ground.
put the positive lead of the meter on the trace you think you want and confirm that you read 13.8 or so volts there.
one last thing.
if you have removed TR24 from the radio, put it back in, as you will probably be squealing with the echo board installed. its a 2SC945 transistor.
if you are sure you did everything right and still have bad squeal, try replacing C18 with a 1000uF 16volt electrolytic capacitor.
you should be able to find it using the service manual.
good luck and feel free to ask any questions here.
LC
