Cobra 29 with an odd problem.

[wjm1129]

I have a 2016 model Cobra 29 ltd classic. When I modulate, the rf meter doesn't move. I switched mics and that isn't the problem. The meter works on receive and swr cal. The only thing I have adjusted is modulation. The radio works great except for the meter on xmit. Has anyone experienced this problem? If so what is wrong? TIA

 

[nomadradio]

Does the meter come up to a steady reading when you key the mike? Or does it drop all the way to the left end of the scale?

Do you have any resources to draw on besides just the radio and mike? A wattmeter? Another radio to listen and hear what is or isn't coming out of this one?

Simply turning a trimmer pot to adjust the modulation limit should not put it off the air.

73

 

[wjm1129]

When I key up to talk there is no movement. There is full movement when I use swr calibrate and swr check. I have a wattmeter and vom and another radio. The Cobra is modulating and sounds normal. Key up wattage is 4 watts.

 

[RCIGuy]

You can try adjusting VR5 while keyed up see if meter moves, might not be set right. Note where its positioned before you adjust in case it does nothing and you can put it back where it was.

 

[wjm1129]

I did that and it didn't change anything.

 

[Handy Andy]

You may have thought you adjusted MOD but instead you may have adjusted the wrong VR


Just reset the pot you thought you were adjusting MOD, back to mid point - then TX, see if you get your TX RF meter back in TX mode - if so, the RX and TX meters - you may have a damaged component.

The Circuit for S meter and TX RF metering is pretty simple - but if one pot is damaged or shorted - and/or turned the wrong way, you may have lose indication in a mode - but the other mode seems to be ok.

Some radios they "clip" the limiter, but if they did it to the wrong diode - well there's your ballgame, just have to resolder a new diode there and clip the RIGHT one they should have done in the first place.

 

[wjm1129]

Nothing has been clipped in this radio. I only adjusted vr4 for modulation. The meter has worked since new until last Thursday.

 

[Handy Andy]

External meter hooked thru - in to a dummy load- shows RF - 4 watts.

Ok, two things suspect; switch or wiring - you get S meter and SWR cal - so is S meter reading from before - has it changed? These two share the same "portion" of the circuit.

D12 is a germanium diode - so ... sorry for the "Horizontal, but it may help us understand more of what may have gone wrong.



The only thing I can see that can go bad, are 3 sections of the TX metering - then the S/RF meter circuit combines into the one line and shows. (Referring to the needle moving - or the "Show" it provides to the operator, that as they TX, the thing swings)

So, you didn't go into a lot of details, but some Cobra 29's came with ANT warm, as well as MOD metering - thinking since you mentioned SWR and CAL seem ok, we don't have something getting sucked out that way.

I'd just unsolder the pot - remove it, place a 3.3K across the two terminals it uses to feed into this averaging circuit that even the RX side uses (C81 and C80) to test RF metering for a quick TX key up.

Does the meter work now? (Just lower) Then - the Pot itself just may have been "torqued" and now has lost the crimp that keeps the variable wiper arm to the substrate - that may be all that is wrong with it - just re-crimp the pot back together and retest the leads - make sure the composition is working.