Cobra 2000 gtl

[my2995dx]

Got this radio 2000gtl now needs work waiting on the new caps to come and audio chip.But this has extra channels in it I want to remove now with this mod to remove it's just the 2 wire on the 8719 I seen a pic online it showed 3 wires on the 8719 plus the ground but is what I want to know with this mod is there any resistors removed or diodes I want to take it back to stock.Its a work in progress no Tx or Rx so soon as the caps come from Klondike Mike's I'll get to work on that

 

[my2995dx]

Question guys on my 2000 I have another radio about 3 ft from it when I transmit on the 2000 I can hear it in my other radio but I have no receive I'm guessing caps still waiting on my caps to come

 

[nomadradio]

In other words, this radio can receive the strong signal from a radio an arm's length away, right?

But can't hear a noise level on an antenna?

I think that's what you mean.

73

 

[my2995dx]

In other words, this radio can receive the strong signal from a radio an arm's length away, right?

But can't hear a noise level on an antenna?

I think that's what you mean.

73

Correct and the Rx light doesn't light

 

[nomadradio]

Rx light doesn't light

The "RX" and "AM" bulbs nearly always burn out first. Good chance that's why it's dark.

Any chance someone tried to "fix" it by turning adjustment slugs at random?

Alignment is always the first troubleshooting step for a weak receiver, even if there is no history of the radio being tweaked.

The transmit problem could easily have that same cause. And even if the problem is a circuit failure of some sort the way it responds to the alignment adjustments becomes a diagnostic clue.

Somebody (else) needs to post a YT vid for this radio, "forensic alignment". First troubleshooting step for a weak radio.

73

 

[my2995dx]

The "RX" and "AM" bulbs nearly always burn out first. Good chance that's why it's dark.

Any chance someone tried to "fix" it by turning adjustment slugs at random?

Alignment is always the first troubleshooting step for a weak receiver, even if there is no history of the radio being tweaked.

The transmit problem could easily have that same cause. And even if the problem is a circuit failure of some sort the way it responds to the alignment adjustments becomes a diagnostic clue.

Somebody (else) needs to post a YT vid for this radio, "forensic alignment". First troubleshooting step for a weak radio.

73

Don't know any history on this I found c142 burnt right by L36 fixed that have to go through it more over.the weekend got this at a sale.

 

[nomadradio]

C142 is a 27pf disc cap in series with L36. Together they make up a 54 MHz 2nd-harmonic trap circuit, meant to reduce TV interference. Not a typical failure.

Makes it sound like lightning, but there would be other casualties if that's what happened.

A burned C142 by itself is a puzzle.

When a radio shows up here for repair that's in a coma, I ask how many attempts have already been made to fix it since it first acted wrong.

The owner might know, might not. But for every pair of hands that was in the radio and failed to make it work, I assume at least one new fault besides the original problem. The average is probably closer to two.


73

 

[my2995dx]

The "RX" and "AM" bulbs nearly always burn out first. Good chance that's why it's dark.

Any chance someone tried to "fix" it by turning adjustment slugs at random?

Alignment is always the first troubleshooting step for a weak receiver, even if there is no history of the radio being tweaked.

The transmit problem could easily have that same cause. And even if the problem is a circuit failure of some sort the way it responds to the alignment adjustments becomes a diagnostic clue.

Somebody (else) needs to post a YT vid for this radio, "forensic alignment". First troubleshooting step for a weak radio.

73

Even the resistor in front R254 was burnt but looking over the rest there is no other burnt marks had to order the caps should have them in a few days want to replace all caps and go from there that way I know there good and for some reason it has a C1307 final I have a 2312 the original 2sc-2312 and some ifr520

 

[my2995dx]

C142 is a 27pf disc cap in series with L36. Together they make up a 54 MHz 2nd-harmonic trap circuit, meant to reduce TV interference. Not a typical failure.

Makes it sound like lightning, but there would be other casualties if that's what happened.

A burned C142 by itself is a puzzle.

When a radio shows up here for repair that's in a coma, I ask how many attempts have already been made to fix it since it first acted wrong.

The owner might know, might not. But for every pair of hands that was in the radio and failed to make it work, I assume at least one new fault besides the original problem. The average is probably closer to two.


73

Ok got new caps in made sure all was good took my time didn't do the freq counter yet but when I turn one the radio the freq counter says 92.2000 what happen

 

[nomadradio]

On the side of the clock/counter module alongside the radio's main pc board is a 4-pin socket with two shielded wires on it. If this comes loose from the header pins on the module, you'll get that number on the display.

The clock/counter module has a particular hazard built into it. The power to the clock is always on, even when the radio is turned off. If you pull that plug with the two shielded wires loose while the line cord is plugged into the wall, this can damage the input circuits in the counter. The counter/clock is on all the time the radio is plugged in. But if the radio power switch is off, this creates a possible surge. Likewise, plugging that connecter back in while the cord is plugged into a wall outlet can also do this.

Never mind how I discovered this.

The "92.200" reading looks puzzling, but it's actually what serves as a zero reading when the counter has no input. Because the counter has to subtract 7.8 MHz from the PLL frequency feeding into it, a 'zero' input doesn't display zero like a normal external counter will do. If you add 7.8 to 92.2, you get 100. But since that's one more digit than it has on it, this is the same as a "zero" reading with no input. For this counter, anway.

Short version: The counter thinks that there is no input feeding it.

The question is "how come?".

73

 

[my2995dx]

On the side of the clock/counter module alongside the radio's main pc board is a 4-pin socket with two shielded wires on it. If this comes loose from the header pins on the module, you'll get that number on the display.

The clock/counter module has a particular hazard built into it. The power to the clock is always on, even when the radio is turned off. If you pull that plug with the two shielded wires loose while the line cord is plugged into the wall, this can damage the input circuits in the counter. The counter/clock is on all the time the radio is plugged in. But if the radio power switch is off, this creates a possible surge. Likewise, plugging that connecter back in while the cord is plugged into a wall outlet can also do this.

Never mind how I discovered this.

The "92.200" reading looks puzzling, but it's actually what serves as a zero reading when the counter has no input. Because the counter has to subtract 7.8 MHz from the PLL frequency feeding into it, a 'zero' input doesn't display zero like a normal external counter will do. If you add 7.8 to 92.2, you get 100. But since that's one more digit than it has on it, this is the same as a "zero" reading with no input. For this counter, anway.

Short version: The counter thinks that there is no input feeding it.

The question is "how come?".

73

Kind of weird the frequency counter worked until I put the new caps in radio when I went.to check it on 12v.I'll have.to go back through it see what's causing this

 

[nomadradio]

Um, okay. That 4-pin header that the two shielded wires plug in to is labeled "J412" on the clock/counter module.

One of the reasons we won't sell rebuilt clock/counter modules for this radio is the risk that the buyer will plug or unplug that connection with the power cord still plugged in to the wall outlet.

The risk is that the buyer will do exactly that, become annoyed that his newly-rebuilt module reads "92.200" and wants to send it back.

Of course, he has no idea that he just blew out the counter's input circuits.

Shutting off the radio with the push-button on the front still leaves circuits with power on them, so long as the power cord is plugged in to a live outlet. The cord has to get pulled from the wall before you can safely molest J412.

Maybe that's what went wrong with your radio, maybe not.

Just wish someone would come up with a reliable test for this failure that doesn't require an oscilloscope. That's the only tool I know to confirm this breakdown when it happens.


73

 

[my2995dx]

Um, okay. That 4-pin header that the two shielded wires plug in to is labeled "J412" on the clock/counter module.

One of the reasons we won't sell rebuilt clock/counter modules for this radio is the risk that the buyer will plug or unplug that connection with the power cord still plugged in to the wall outlet.

The risk is that the buyer will do exactly that, become annoyed that his newly-rebuilt module reads "92.200" and wants to send it back.

Of course, he has no idea that he just blew out the counter's input circuits.

Shutting off the radio with the push-button on the front still leaves circuits with power on them, so long as the power cord is plugged in to a live outlet. The cord has to get pulled from the wall before you can safely molest J412.

Maybe that's what went wrong with your radio, maybe not.

Just wish someone would come up with a reliable test for this failure that doesn't require an oscilloscope. That's the only tool I know to confirm this breakdown when it happens.


73

It was unplug when I did the caps I was only using the 12v to test after.It went dark after I called the radio didn't even do the freq counter yet so I did that and still dark will have to go back through it and see if i messed up