Cobra 2000 No voltage at Test points 7 and 8

[guitar_199]

Not to muddy the waters any more than they are.....but......

My two brain cells voted.....and they think it might be interesting to unsolder/remove the driver....... at least the base pin IF you can do that..... to see if the PAD for the base IS GETTING the RF to turn the transistor on.

Just "calling in some plays" from "halfway up in the bleachers"....

 

[Brian G]

Not to muddy the waters any more than they are.....but......

My two brain cells voted.....and they think it might be interesting to unsolder/remove the driver....... at least the base pin IF you can do that..... to see if the PAD for the base IS GETTING the RF to turn the transistor on.

Just "calling in some plays" from "halfway up in the bleachers"....

I’ll try anything. Thanks.

 

[guitar_199]

My thinking is...... if the driver is shorted internally pulling that signal down.... when you unsolder the base.... it SHOULD pop RIGHT back up.

If it doesn't..... that is what HA is getting at here. SOMETHING is wrong with the path (meaning the copper/component path from the cap after L44) that is drawing the RF signal level down. It can be a tough "row to hoe" but this is the only way to get there!

Best of luck my friend....

 

[Brian G]

My thinking is...... if the driver is shorted internally pulling that signal down.... when you unsolder the base.... it SHOULD pop RIGHT back up.

If it doesn't..... that is what HA is getting at here. SOMETHING is wrong with the path (meaning the copper/component path from the cap after L44) that is drawing the RF signal level down. It can be a tough "row to hoe" but this is the only way to get there!

Best of luck my friend....

Sooooo here is something weird. I unsoldered that base leg. There is 0.7 volts at the pad which is what it should be according to Sam’s. But while I was putting my VOM probe on the base pad while it was keyed up, the probe slipped and for a second it bridged between the collector and the base pads and my other meter set up to check the bias all of a sudden popped up and gave near normal reading! I quickly and carefully duplicated it a few times. Could there be a broken connection between those 2 legs? It looks like from the Sam’s that there is a junction between c200/R209/c156. Is that possible where the problem is? The board over there is a bit beat up so I couldn’t really visualize the traces. But if that’s the case, I need to restore that connection and maybe I’ll have it but I didn’t want to do that without seeing what you all thought first so I don’t create a new issue. Let me know what you think.

 

[kaos513]

I would check the voltage regulator

 

[Handy Andy]

You ask a GREAT question.

That is the NFB circuit...it helps to keep the 1307/1969/2312 (I've seen at least these types and a 2078) from seeing excessively high peak power - the 2166 is capable of being a 4 watt FINAL on it's own - so that tells you the power capacity.

Just look at several different Uniden radios from the older days, including 510/520 and the 538 - you'll see where this and a 2086 did the job pretty effectively...

Schematically, this is what it functions as...

NBF may seem unimportant, even diminutive
- but it is a necessary requirement.
That is, if you wish to have parts in radio's last longer.
Since this radio is no longer made, to leave this out may
be a BIG mistake...
​

You should keep these in there, but replace them with fresh nonetheless.

Break the connection at the cap and resistor - this may wind up being the "short to ground" you'll have to repair later. See if power returns like you found earlier without them in place.

Clean up that area - there is board groudn next to it, so strands, shards or other frayed wiring - these spots are open to the board to straddle two components to form a loop circuit - wise.

• - designed to control the level of power present in the driver, so the whatever is used behind it, doesn't blow up from too much power or worse, becomes a problem forming secondary harmonics and even making your radio sound horrible if you don't keep it in there.

You have some time to fix this but the location is here...right in front of the Driver...

Notice that the Cap and Resistor location is VERY CLOSE
to the RF and Board ground.
CARE NEEDS TO BE TAKEN SO RF POWER
AND DC POWER Do Not SHORT out to GROUND Here
The Results can be catastrophic!​

 

[Brian G]

You ask a GREAT question.

That is the NFB circuit...it helps to keep the 1307/1969/2312 (I've seen at least these types and a 2078) from seeing excessively high peak power - the 2166 is capable of being a 4 watt FINAL on it's own - so that tells you the power capacity.

Just look at several different Uniden radios from the older days, including 510/520 and the 538 - you'll see where this and a 2086 did the job pretty effectively...

Schematically, this is what it functions as...

View attachment 44398

NBF may seem unimportant, even diminutive
- but it is a necessary requirement.
That is, if you wish to have parts in radio's last longer.
Since this radio is no longer made, to leave this out may
be a BIG mistake...
​

You should keep these in there, but replace them with fresh nonetheless.

Break the connection at the cap and resistor - this may wind up being the "short to ground" you'll have to repair later. See if power returns like you found earlier without them in place.

Clean up that area - there is board groudn next to it, so strands, shards or other frayed wiring - these spots are open to the board to straddle two components to form a loop circuit - wise.

• - designed to control the level of power present in the driver, so the whatever is used behind it, doesn't blow up from too much power or worse, becomes a problem forming secondary harmonics and even making your radio sound horrible if you don't keep it in there.

You have some time to fix this but the location is here...right in front of the Driver...

View attachment 44397

Notice that the Cap and Resistor location is VERY CLOSE
to the RF and Board ground.
CARE NEEDS TO BE TAKEN SO RF POWER
AND DC POWER Do Not SHORT out to GROUND Here
The Results can be catastrophic!​

Yeah I was poking around there after I posted. I think I smoked the driver again. WTF!!!!! I need to get another one and hope that's all I did. Right now from checking, everything else appears to be ok. SOOOOOO tired of this. Anyone want to buy a parts only Cobra 2K? LOL!!

 

[Handy Andy]

I love one, but I couldn't pay you enough...you put a lot of time into it - so you're best to keep the radio and get it working - then decide to sell it off - a six figure amount on the listing would tell the rest of the world...

 

[Brian G]

I love one, but I couldn't pay you enough...you put a lot of time into it - so you're best to keep the radio and get it working - then decide to sell it off - a six figure amount on the listing would tell the rest of the world...

LOL! Thanks for the help so far. I will get back to you once I get the new driver in (should have it in tomorrow or Friday).

 

[Brian G]

Do you happen to have a good closeup of the solder side of the board at the driver? Like taken right over the top of that area to see the traces.

 

[1iwilly]

brian this what mine looks like

Do you happen to have a good closeup of the solder side of the board at the driver? Like taken right over the top of that area to see the traces.

 

[Brian G]

brian this what mine looks like View attachment 44423

Great thank you!! Also what is the value of that green cap over near the right edge?

 

[Handy Andy]

That varies @Brian G - this helps "tune" so be ready with several values - and choose the one that allows for the best low-level SSB power "transfer" - use your voice into your mic, as whispers and low-level ambient sounds work best for this - to find the best transfer peak power.

What I've used are variable caps - trimmers, adjustable from ~7pF to ~40pF - Jameco has several types or ranges of values.

It shows 3 legs, but you use two - like on a potentiometer - only it's a capacitor One side to Twisty other to Pre-Drivers RED leg of L44

You can either use it to FIND the right value - turn - tune to trim to find the peak, then sub in correct FIXED value.

Or if you're keeping it inside and in a controlled environment - use it and trim for best peaking results, and just leave it in there. It doesn't handle a lot of power, but it will work just fine in this setup to help with the peaking of this section.

 

[Brian G]

That varies @Brian G - this helps "tune" so be ready with several values - and choose the one that allows for the best low-level SSB power "transfer" - use your voice into your mic, as whispers and low-level ambient sounds work best for this - to find the best transfer peak power.

What I've used are variable caps - trimmers, adjustable from ~7pF to ~40pF - Jameco has several types or ranges of values.

It shows 3 legs, but you use two - like on a potentiometer - only it's a capacitor One side to Twisty other to Pre-Drivers RED leg of L44

You can either use it to FIND the right value - turn - tune to trim to find the peak, then sub in correct FIXED value.

Or if you're keeping it inside and in a controlled environment - use it and trim for best peaking results, and just leave it in there. It doesn't handle a lot of power, but it will work just fine in this setup to help with the peaking of this section.

Maybe dumb question, which 2 legs do I use? Does it matter? I have a few like this so once I get the main problem resolved I’ll go back and revisit this. Thanks.

 

[Handy Andy]

Center to one side - Center is part of the variable - across the two other-outer legs are the fixed value.

So these trimmers are also "dividers" when it comes to RF - but that is another story for later.