Cobra 142 GTL

[vswr]

Here is that cap that seens to do nothing.why was it installed during the hack?

 

[vswr]

Here Ivreplaced the ct3 trimmer and put the 11.11125 crystal back into its home. Notice the blob of solder on the top ofvthat crystal? It was attacedvto the top of 2 other crystals using solder wick. A real mess and obviously overheated.

 

[vswr]

I have not touched ct1 or ct2 at all. Im still not there becausenof my 20k and clarifier issue. You can seevthe blob of scum that was covering that diode. Im still goingbto clean it properly.

 

[brandon7861]

If transmit is spot on, you don't have a problem with the 11MHz crystal. That has to work to have proper TX.

This is a single-conversion receiver, meaning AM signals coming in are mixed with the VCO (nothing else), passed through a couple filters, and directly detected at 7.8MHz.

You say you have to pull the VCO to 34.775 to receive ch1. This means that either your crystal filter moved by 10kHz (really doubt it, and SSB would be all screwed up), or your test transmitter is transmitting off by 10kHz.

edit: and that crystal isn't burnt, thats just rosin flux

 

[brandon7861]

I would definitely check that test transmitter for a 10kHz switch. See what it outputs.

You mentioned doing this at a shop. Is this a radio/electronics shop with other electronics gurus? Perhaps one of them sidelines as a comedian? Thats something I think I might do to an apprentice just to see where they were at. Shift their test radio by 10kc lol.

 

[vswr]

AM transmit is good at 7.800mhz. Channels all transmitnon freq. Its the rx thats 10k off. Cant seem to figure this one out.

 

[vswr]

If transmit is spot on, you don't have a problem with the 11MHz crystal. That has to work to have proper TX.

This is a single-conversion receiver, meaning AM signals coming in are mixed with the VCO (nothing else), passed through a couple filters, and directly detected at 7.8MHz.

You say you have to pull the VCO to 34.775 to receive ch1. This means that either your crystal filter moved by 10kHz (really doubt it, and SSB would be all screwed up), or your test transmitter is transmitting off by 10kHz.

edit: and that crystal isn't burnt, thats just rosin flux

I pick up everyone from 38L on 39L. Superbowl is on 7. 28 is now 29. My SDR is my test radio. Its dead on. The problem is in the 142 receive. No doubt about it.

 

[vswr]

AM transmit is good at 7.800mhz. Channels all transmitnon freq. Its the rx thats 10k off. Cant seem to figure this one out.

I would definitely check that test transmitter for a 10kHz switch. See what it outputs.

You mentioned doing this at a shop. Is this a radio/electronics shop with other electronics gurus? Perhaps one of them sidelines as a comedian? Thats something I think I might do to an apprentice just to see where they were at. Shift their test radio by 10kc lol.

I have my own shop. Im alone there

I would definitely check that test transmitter for a 10kHz switch. See what it outputs.

You mentioned doing this at a shop. Is this a radio/electronics shop with other electronics gurus? Perhaps one of them sidelines as a comedian? Thats something I think I might do to an apprentice just to see where they were at. Shift their test radio by 10kc lol.

If transmit is spot on, you don't have a problem with the 11MHz crystal. That has to work to have proper TX.

This is a single-conversion receiver, meaning AM signals coming in are mixed with the VCO (nothing else), passed through a couple filters, and directly detected at 7.8MHz.

You say you have to pull the VCO to 34.775 to receive ch1. This means that either your crystal filter moved by 10kHz (really doubt it, and SSB would be all screwed up), or your test transmitter is transmitting off by 10kHz.

edit: and that crystal isn't burnt, thats just rosin flux

Transmit is spot on.

 

[brandon7861]

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?

 

[vswr]

I pick up everyone from 38L on 39L. Superbowl is on 7. 28 is now 29. My SDR is my test radio. Its dead on. The problem is in the 142 receive. No doubt about it.

I ised your charts to check the VCO frequencies. Even the skips are at a 10k jump. One fellow said I should replace the 8719 but Its perfect on thevtruth table pin outs. It hascto be a coil, diode, crystal or cap. Disc caps are funny things. Ive seen them shorted, hi and low resistnce short, or open as you would expect, though not working. Diodes easy, coils easy, tuning caps easy tuning coils could be tricky if they have tiny caps inside. One thing for sure is my CT3 will not tune to the sams spec, my ct1 same deal. Both USB. My LSB I can tune statically because if I put them directly on frequency my clarifier has to fetch them way off center. Im going to study your notes and do more tests. Pull out parts and test them individually. I appreciate the time you've spent helping me, but now I think I've worn out my welcome with this radio as its just too messed up. Thanks again and 73s.

 

[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?

I'll get that for you asap. Im taking a break for now to cogitate this conundrum.

 

[vswr]

Time for me to put in my 2¢...........

Try replacing L24 to see if your 10K problem goes away, after all it is part of the clarifier circuit.

Are you also using an Oscilloscope as called for in the alignment section for L14 & L18? (This can't be done by ear.)

Have you verified that the setting for ct1 & ct2 are correct even though you say you haven't adjusted them?

Also need pictures (of the bottom side of the board) of the VCO and clarifier circuit area, also to see what that cap between crystals is all about too.

Good Luck and 73. . . . .

Interesting you say that. I just noticed that the slug in L24 is cracked! Now, i know that this radio has been golden screwdrivered.

 

[doffo]

Down with cracked slugs! lol.

 

[vswr]

Down with cracked slugs! lol.

Yeah. I just saw it. Now I know some effing clown yook a jewelers screwdriver to it and most likely to every slug.

 

[vswr]

Another interesting find. When the clarifier if tuned to 9 oclock and 8 oclock, inpick up channel 38 perfectly while Im on channel 40. What a mess!