Cobra 142 GTL

[brandon7861]

I am starting to think you have a VCO problem. Turning L13 should only momentarily change the frequency with the PLL bringing it right back to where it was (hopefully before you even notice). If you are turning L13 and the frequency changes without moving right back to what it was, the VCO varactor on the UHIC007 could be shot.

Could also be the PLL's PD output. Does the voltage on TP9 change when turning L13?

 

[vswr]

Yes. The voltage changes. Going by the sams im supposed to lock in at 5v but i remember mentionning that it woudnt lock into anything until around 3 volts. Im pretty sure its around the VCO area. I will have to see if there is a cap inside the can or pull one from another radio donor

 

[vswr]

I am starting to think you have a VCO problem. Turning L13 should only momentarily change the frequency with the PLL bringing it right back to where it was (hopefully before you even notice). If you are turning L13 and the frequency changes without moving right back to what it was, the VCO varactor on the UHIC007 could be shot.

Could also be the PLL's PD output. Does the voltage on TP9 change when turning L13?

UHI007. What is that the part number of something?

Edit: I see it on thecschematic. I'll have a look at the circuitry.

 

[brandon7861]

Its the VCO chip, a circuit board about an inch long and half an inch wide that stands on edge. Usually covered in black truck bed liner.

but if it locks at 3v and L13 can be moved without permanently shifting the frequency, its probably fine.

 

[vswr]

Yeah. I saw it on the schematic. Is there a varactor inside of it?

Looking at the schematic, I see where L13 hooks up to it. Im wondering why I get such avstrong dignal that is exactly 10k off. L13 has no cap inside from the schematic, and if all that is controlled by the 11.1125 crystal, im thinking maybe the crystal has shifted down somewhat? Considering my heat test brought everything into perspective. CT3 doesnt move the frequency very much at all.

The clarifier also works with that crystal and the TX section. To me its the crystal circuit or coil circuit. Thoughts?

 

[vswr]

Its the VCO chip, a circuit board about an inch long and half an inch wide that stands on edge. Usually covered in black truck bed liner.

but if it locks at 3v and L13 can be moved without permanently shifting the frequency, its probably fine.

Grasping at straws here. How about the channel switch? Could it be a cause ofvthe shift? Although when I did my data tests, the highs and lows appeared correct as per the truth table. Hmmmmmmm...........

 

[vswr]

Im wonderingnif thisvradiobwhich had uppers and lowers also got broadbanded? There is a disc cap soldered accross avcut run that has crappy solder work. Im gonna find out where it appears in the schematic.

 

[brandon7861]

If the trimmer has little to no effect but the clarifier working on the varactor does, then you have a bad trimmer.

...and a high frequency does result from a lack of capacitance.

 

[vswr]

If the trimmer has little to no effect but the clarifier working on the varactor does, then you have a bad trimmer.

...and a high frequency does result from a lack of capacitance.

I replaced it twice. It tests good on the bench. Early days into this project. I even swapped out the trimmer for a higher pf then went back to a new 20pf. They cant all be bad. There appears to be another cspbin parallel with the trimmer on the schematic.

 

[brandon7861]

Is that electrolytic thats tcked on to the crystal filter go to R72? What does that cap connect to??

 

[vswr]

Is that electrolytic thats tcked on to the crystal filter go to R72? What does that cap connect to??

I think it does. I removed one side and didnt notice any changes

 

[vswr]

Is that electrolytic thats tcked on to the crystal filter go to R72? What does that cap connect to??

There appears to be some sort of diode with what looks like a SMD diode hooked to it. Its on the right side of this crystal. Image might not show it until you click on it. Its in series with a diode which looks like a varactor diode. Has a green band. Could be a broad band thing. I put a short accross it. Not much of a change.

 

[brandon7861]

Not seeing that in this picture. I see nothing but the edge of a big disk cap to the right of the crystal

 

[vswr]

Better shot. Ive since cleanedvoffvthat blob of solder and flux. See the small square?

 

[vswr]

It could be a home made type of varactor. Diode and capacitor. But its mote. It proved to make a minor clarifier change when bypassed