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Cobra 142GTL alignment Q?


Ok this strange ill let the radio warm up more and try agen...

The clarifier is unlocked but it's done the same way as my uniden Washington..

I know its not the counter i had it varafied at a local shop and it is dead nuts with my Ts-2000...
 
this is strange for sure. if you align it with the clarifier in the 12 o clock position it should not move to the 2 o clock position after you align it. this is a strange one to me. I am at a loss. hope you get it figured out and be sure to leave info as what you had to do to correct it.
just a thought, you said it has a 11.3258 crystal in it. I assume it has extra channels in it since that is what you do to the 148 in most cases. it has been a couple years or so since I put channels in a 142 radio but I may be wrong but you had to cut a ground loose on I think pin 9 of the PLL to get it to align properly with the 11.3258 crystal. just thinking out loud here.
 
sonoma said:
this is strange for sure. if you align it with the clarifier in the 12 o clock position it should not move to the 2 o clock position after you align it. this is a strange one to me. I am at a loss. hope you get it figured out and be sure to leave info as what you had to do to correct it.
just a thought, you said it has a 11.3258 crystal in it. I assume it has extra channels in it since that is what you do to the 148 in most cases. it has been a couple years or so since I put channels in a 142 radio but I may be wrong but you had to cut a ground loose on I think pin 9 of the PLL to get it to align properly with the 11.3258 crystal. just thinking out loud here.
Click to expand...

yea some one put extra channels in it but it was a mess so i removed them and just put 1 switch in for 4 up..
ill play with it today.
 
I was just thinking and are you sure the crystal is a 11.3258 and not a 11.325. I ran into this a few years ago and the crystal was not a 11.3258 and was causing a problem. I put it in my crystal tester and sure enough it was throwing me off just a little.
 
It's possible someone already modified the radio, beyond just changing resistors.
I would look up Cobra 142 GTL "slide/clarifier mods", and start looking at the parts designators mentioned, compare that to what's in the radio.

If they've changed the varactor diode to something other than factory, or simply added an inductor in series w/ the factory varactor, the clarifier position will likely not be centered after alignment. (at least this is what i've found in my own experience)
 
The sequence for setting the clarifier to 12 o'clock must start by setting USB first.

The capacitor CT3 that sets USB is always in the circuit for the other two modes. Turning CT3 will change the settings of L19 and L20, so you have to set CT3 first.

Only after setting CT3 for USB will the other two adjustments L19 and L20 set properly. Doesn't matter what order you set L19 and L20, so long as CT3 was set first.

That radio was built with a 11.1125 crystal. To make the channels line up, pin 10 of the MB8719 PLL was grounded at the factory. The 11.325 works, but only after that ground connection on pin 10 is broken. Changing the crystal is usually done to obtain upper channels you'll get by grounding pin 10 with a switch. The original 11.1125 crystal just can't get you very far above channel 40. Grounding pin 10 with a switch gets you up to 28.045 MHz with the 11.325 crystal.

If the value of fixed resistors in the clarifier circuit have been changed, this will affect the position of the clarifier knob to get the channel centered. This radio does not "stretch" the clarifier a whole channel very readily. Even so, folks will hack this circuit in the attempt anyway.

Never underestimate how many circuit details can be altered in the PLL section of a CB. There are more "secret sauce" tricks for this than you can count.

73
 
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nomadradio said:
The sequence for setting the clarifier to 12 o'clock must start by setting USB first.

The capacitor CT3 that sets USB is always in the circuit for the other two modes. Turning CT3 will change the settings of L19 and L20, so you have to set CT3 first.

Only after setting CT3 for USB will the other two adjustments L19 and L20 set properly. Doesn't matter what order you set L19 and L20, so long as CT3 was set first.

That radio was built with a 11.1125 crystal. To make the channels line up, pin 10 of the MB8719 PLL was grounded at the factory. The 11.325 works, but only after that ground connection on pin 10 is broken. Changing the crystal is usually done to obtain upper channels you'll get by grounding pin 10 with a switch. The original 11.1125 crystal just can't get you very far above channel 40. Grounding pin 10 with a switch gets you up to 28.045 MHz with the 11.325 crystal.

If the value of fixed resistors in the clarifier circuit have been changed, this will affect the position of the clarifier knob to get the channel centered. This radio does not "stretch" the clarifier a whole channel very readily. Even so, folks will hack this circuit in the attempt anyway.

Never underestimate how many circuit details can be altered in the PLL section of a CB. There are more "secret sauce" tricks for this than you can count.

73
Click to expand...


yes i do my USB adjustments on CT3 first i seen it was tied to the crystal in the schematic.

right now Pin 10 is cut for the normal 40 Ch

I would think just setting the clarifier to 12 and getting the adjustments would just fall in to place but i guess not..
 
The counterclockwise (left-hand end) lug of the clarifier control normally goes to a 3.3k resistor R415. The other end of R415 goes to ground. This restricts the end-to-end coverage of the control. If R415 has been "jumped" to expand the range and the clarifier control can turn all the way down to ground, this will skew that 12-o'clock setting to one side.

73
 
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ok it is working good now o_O i think it may had some thing to do with the temp in the room and having a fan in the room when i was setting it up..
I had it running for 1 hr and when i had the lid off it cooled down.. i may have taken to long to make the adjustments..
 

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