cobra 29ltd '03 china, off freq by about 9khz low

[Uncle Ronnie 336]

what could be potential causes of this? (other than made in china)
haven't cracked it open yet, was told it was used in the operation of baling hay in VT so it was a former work rig.

 

[groundwire]

cb radios are never spot on from the factory. probably just a half ass alignment from the manufacturer and then getting beat around in a work truck for almost 20 years in the hot and cold. 29's are pretty solid rigs, probably just needs a touch up. easy job on a 29

 

[Woody-202]

what could be potential causes of this? (other than made in china)
haven't cracked it open yet, was told it was used in the operation of baling hay in VT so it was a former work rig.

maybe they put a switch in to drop it 10kc to get the "A" channels

 

[Low_Boy]

Normally a bad solder connection at the crystal or around that area.

 

[nomadradio]

I have seen the 10.24 MHz crystal drift off frequency, but not all that often. Making sure the tuning slug in the can behind the crystal L24 still turns freely is where I would start. And if that gets it close, but not close enough, suspect the crystal.

And if the slug is cracked and seized in place at one end of its travel, maybe that's the root of the error.

73

 

[Handy Andy]

Better check the "Delta Tune" knob (if it has one) see if the pots been damaged or otherwise repurposed to serve another purpose (ECHO - e&c)

When the Delta Tune is removed, this shift happens.

 

[nomadradio]

Andy's right. If the tuning voltage from the Delta-Tune circuit is lost, the channel frequency will be low. Didn't think of that.

73

 

[Uncle Ronnie 336]

the pot is intact, theres the 8.6v leading to it.

 

[Handy Andy]

Is the crystal 10.240 or 10.000MHz? (Just kidding)

But in light of this 9kHz low, the Delta tune knob is just that, but you can see if it's tracking right - do this check in RX and TX modes - look for voltage on the pot while switching modes (into a dummy load) - only RX would have it - then go to the "pair" of steering diodes located by L21 and L18 - (TP5) that also looks for 8V - so the RX voltage and TX voltages THERE should be nearly the same where those 2 diodes meet. (Check on their banded end)

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IF you don't have them consistent with each other, you'll have to find out why.

So that might mean a tuning cap is gone or going out.