Cobra 142 GTL

[brandon7861]

I wonder what type of phase detector is inside the 8719 chip. Can the clarifier being out of whack be causing the PD to lock on to a harmonic?

I would go over the clarifier circuit with a fine-tooth comb. That was the real reason for my detailed explanation of that circuit. Not necessarily to modify it, but to find what was modified.

 

[vswr]

I plan on it trust me. Im just so fried right now having put a solid week of at least 5 hours a day into it so I need a little timeout. I will get you that d36 voltage shortly. Tx Am channel 19 and my 7.800mhz is dead on. I donplan to tear out the entire clarifier and test each part 1 by 1. I will keep you posted. Thank you for soooo much,excellent support!

 

[vswr]

Tlright now, it stands that I put the open clarifier back correct. Im taking an 8 volt source from the receiver at the point where the sams says it goes, a 3.3k resistor to ground was also installed, the original pot I replaced. Didnt change a thing. The transmit is working fine. The receive off by 10k.

The hack mod had the positive 8 volts taken from the cap beside the PLL chip. Thev3.3k resistor was not installed. Instead, the wire was grounded. I found a cut wire in the bundle. Nicely tucked in. Im gonna open the bundle and trace it back. Its a white wire.

 

[vswr]

I wonder what type of phase detector is inside the 8719 chip. Can the clarifier being out of whack be causing the PD to lock on to a harmonic?

I would go over the clarifier circuit with a fine-tooth comb. That was the real reason for my detailed explanation of that circuit. Not necessarily to modify it, but to find what was modified.

Im thinking that the outputs are all correct. The highs and lows all check out. Even the skips check out. Thats what makes mevthink that the chip is fine. Ibdid test the output of the chip on channel 19 and its 27.175. 20 skips as 19 would normally to 27.195!

I heated up the crystal and I was able to get it to dial in but thats cheating and would probably throw off the AM and LSB to the point of not being tunable.

I checked D36 andbits 3.27V. On 19.

 

[vswr]

Correction 3.37v

 

[brandon7861]

In both RX and TX. The idea was to see if there is a difference, to see if the clarifier has the ability to provide the same voltage as TX, and then to see if the channels are still off in RX

 

[vswr]

Channel19 L13 frequency. I hear the clowns from 38L on 39L. AM, is also offset by 10 k.

 

[vswr]

In both RX and TX. The idea was to see if there is a difference, to see if the clarifier has the ability to provide the same voltage as TX, and then to see if the channels are still off in RX

Oh. Ok. Wasn't sure. I will get those in the morning. You want them centered in rx and tx AM only?

 

[vswr]

Perhaps I misunderstood earlier. I have been under the assumption that the VCO is outputting the same thing in TX and RX. Is that not true? If TX and RX are different at the VCO, it has to be something in the clarifier.

What is the voltage at the anode of D36 in RX and TX?

The anode is giving me .56 volts. The cathode is 3. 3 volts rx and tx is 3.7. I checked some components today and they are all good readings.

 

[brandon7861]

Oh crap, I see my typo. Yes, I meant cathode lol.

Can you make the cathode 3.7v in RX by adjusting the clarifier?

If so, can you then see if RX is still off by 10kHz with both voltages matching?

 

[vswr]

Thats exactly why I removed the open clarifierbmod and put the radio back to factory. To isolate the rx and TX. I will take a few measurements. Give me a moment...

 

[vswr]

My bad. The TX and RX are both off by 10k. This leads me back to L13 and its associated circuitry. D36, lsb, 19, center is 3.21v, left is 1.19, right is 7.48. Anyhow, I figured out something here.. with L13 adjusted to receive maximum freq level, and Ct3 as High as I can getnit close to the correct freq, I tune the slug of L19 to the absolute top to where its literally setting on top, and clarifier hard right, I can get channel 38 lsb just coming in. Im using the 111 guy to get my signal. I get as close as 27.3798.

Problem is and always was, I cannot tune L13 to get the freq that Im supposed to see. The strongest signal coming out of L13 aligns me 10k lower. Im definitely not on any adjacent freq. Cant be. 10k lower is just too strong and there is no harmonic that works.

Back to square 1.

 

[vswr]

Pardon the bad leds. Its 38L.

 

[vswr]

Slug resting on can.

 

[vswr]

Clarifier hard right