Cobra 139xlr help

[Gnommad]

Hi guys, i am super new to the hobby, and have some questions. I got this for free from a friend, and have no idea what to do with all the knobs/switches. I do not seem to get any reception, but i might be doing things terribly terribly wrong.
what i tried was... i have a ac/dv inverter in my truck, so i plugged it in there, and used the antenna from my current (cheapo uniden) cb. i also used the mic from the same unit. i noticed that when talked the swr/mod meter would move accordingly. oh, i have the settings at:
anl, off
cb (not pa)
rf/mod.
also i have the radio set to am, not usb or lsb.
anyway, when i talk, the swr/mod meter moves, but i dont get any reception, not even static. i have the squealch all the way down, and the gain all the way up, still no static or anything. when i hook everything back up to my uniden, i get chatter on channel 6 (always someone on there) but again, i get nothing on the cobra.
i have a couple questions:
will this unit work in a vehicle? the antenna is grounded, do i need to ground the unit as well?
why do i need to plug the mic in to get reception?? (i noticed this on the uniden)
thanks guys!

 

[Dipole]

It cold be that the mic is pinned differently from 1 radio to the other. I would start there. Some radios depending on the circuitry require the mic to complete the audio circuit some don't.

 

[Gnommad]

ok, so i'm super duper new, how do i see how my mic is pinned? also how do i tell how the unit wants my mic to be pinned?

 

[357magnum]

If you get it working other than its size I thought that model had a 12v plug on the back it would work in you vehicle .

 

[Robb]

http://www.cbtricks.com/radios/cobra/139xlr/index.htm

 

[Gnommad]

ok, so there is not a specific place to ground the unit? i didnt see a green screw or anything like that on the back.... there is a three pronged male type plug thing on the back of the unit, i'll look at the schematics in the post above to see about both the mic, and what those wires are for.

just a noob question, why does the mic need to be plugged in, in order to recieve transmissions?

 

[Gnommad]

duh, just looked at the mic, its made by cobra. probably a few years newer, but is it safe to assume that any cobra mic is properly wired for any cobra radio?

 

[357magnum]

The 3 prong plug is the 12 v plug I was talking about if you don't have the "cobra " plug an hook it up wrong you will fry the radio !

 

[Dipole]

duh, just looked at the mic, its made by cobra. probably a few years newer, but is it safe to assume that any cobra mic is properly wired for any cobra radio?

NO!just because it is a 4 pin it is no guarantee and you can actually do damage to the radio in some instances if it is wrong. However in this case your fine.

 

[Gnommad]

ok, so as far as i can tell, the mic is fine, where would i look next?

 

[357magnum]

Any sound at all ? Is the speaker Good ? It is an old radio moisture does crazy thing to the caps an such .

 

[Gnommad]

i think the speaker is good. the caps appear to be in good shape via visual inspection, i know they mushroom out a little on top when they go. i may show my ignorance here, but seeing as how i dont seem to be receiving any signal (the s/rf pwr meter never twitches) should i trace the wires from where the antenna comes in, and test the components somehow?

 

[Gnommad]

or is there a component which is known to go bad with age on a unit like this where i should look first?

 

[357magnum]

If you have it connected in the vehicle next to the other radio that works an is connected to the antenna set the 139 close by with both radios on the same channel without the antenna hooked to the 139 key the mic on the good radio you should be able to hear something if not you got some serious work to do . lol

 

[Robb]

First thing to do is to try the radio in PA mode with that mic. If you get sound out; then you know you have a receive problem.

Next, you said you don't know how to use the controls. If that is so; then check the squelch knob by making certain that it is turned all of the way to the left.

When you have the radio hooked up to the antenna in AM mode; do you see the meter moving at all on ch 19? Change channels and see if the meter is moving/changing at all.

If you didn't get any sound out of the radio in PA mode; then either you mic is wired wrong for that radio (see my first post; that link has the mic wiring for that radio/mic). Or the internal speaker isn't working.

If the needle is moving/changing at all in AM mode; then the radio is receiving.
If the needle is moving in receive/AM mode and you have no audio out of the radio and the mic is wired correctly; then there is a fair chance that the audio amp is blown.

Or one of the caps have failed. Caps don't have to bulge - to fail. They also fail because they dry out inside due to age and being exposed to extreme temps - both cold and hot.

This old radio is a classic, since you paid for very little for it and it is a keeper; then it might be worthwhile for you to send it to a shop to give it what it needs. Radio makes a decent base station radio; but if you want to run it in your car; then more powa to ya . . .