Cobra 2000 No voltage at Test points 7 and 8

[guitar_199]

By the way.... do you have all of the CB Tricks content?

http://www.cbtricks.com/radios/cobra/2000gtl/index.htm

 

[Handy Andy]

To help you both...

Also - looking at this link...
https://www.worldwidedx.com/threads/cobra-2000-help.261424/#post-758519


Which contains this...

and the Mode / SWR 4 pole switch layout of a 148...

​

It is best to do a continuity check.,

Start by checking continuity at TP7 and 8 routing back to the posts back at the Power Choke, look at your traces, you'll find a wire from there that goes to the front panel - THERE IS YOUR COMMON at the MODE switch.

The Power Choke provides a Separate POWER supply which then supplies Pin 1 Audio Chip, and R193 - it shows continuity, now you know where the R193 leads are, then trace OTHER SIDE of R193 back to a wire that goes to the front panel to MODE switch - this is your AM REGULATOR output - ties to COMMON back to Power Chokes TP7 and TP8.

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

 

[guitar_199]

Absolutely sweet!!!! Thank you!

From what I have seen the inputs to that switch segment look good..... just NOTHING is coming out of it's common pin.... no matter which mode he selects.
I have been wanting a more "rear looking" picture of that switch and THIS has it..... along with a bunch of other handy info.

Thank you sir!

I wish I was there by his side........

so many things occur so quickly..... but "long distance/remote troubleshooting" just takes time.......

Thanks again!

To help you both...

View attachment 44052
Also - looking at this link...
https://www.worldwidedx.com/threads/cobra-2000-help.261424/#post-758519


​

It is best to do a continuity check.,

Start by checking continuity at TP7 and 8 routing back to the posts back at the Power Choke, look at your traces, you'll find a wire from there that goes to the front panel - THERE IS YOUR COMMON at the MODE switch.

The Power Choke provides a Separate POWER supply which then supplies Pin 1 Audio Chip, and R193 - it shows continuity, now you know where the R193 leads are, then trace OTHER SIDE of R193 back to a wire that goes to the front panel to MODE switch - this is your AM REGULATOR output - ties to COMMON back to Power Chokes TP7 and TP8.

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

 

[guitar_199]

And there is a pot o'gold in that statement!

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

 

[Brian G]

And there is a pot o'gold in that statement!

Voltage at tr42 emitter/41 base is 6.4 volts. Voltage at tr42 base is 6.8 volts. However! Both are variable as you adjust VR10. Incan adjust them by turning vr10 to get basically zero volts there to well over 8. Should those be adjustable in that manner? f I lift the base pin of tr41 off the solder pad, it shows 6.2 volts and the pad shows 13.8.

 

[Brian G]

To help you both...

View attachment 44052
Also - looking at this link...
https://www.worldwidedx.com/threads/cobra-2000-help.261424/#post-758519


Which contains this...

and the Mode / SWR 4 pole switch layout of a 148...

​

It is best to do a continuity check.,

Start by checking continuity at TP7 and 8 routing back to the posts back at the Power Choke, look at your traces, you'll find a wire from there that goes to the front panel - THERE IS YOUR COMMON at the MODE switch.

The Power Choke provides a Separate POWER supply which then supplies Pin 1 Audio Chip, and R193 - it shows continuity, now you know where the R193 leads are, then trace OTHER SIDE of R193 back to a wire that goes to the front panel to MODE switch - this is your AM REGULATOR output - ties to COMMON back to Power Chokes TP7 and TP8.

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

Voltage at tr42 emitter/41 base is 6.4 volts. Voltage at tr42 base is 6.8 volts. However! Both are variable as you adjust VR10. Incan adjust them by turning vr10 to get basically zero volts there to well over 8. Should those be adjustable in that manner?

To help you both...

View attachment 44052
Also - looking at this link...
https://www.worldwidedx.com/threads/cobra-2000-help.261424/#post-758519


Which contains this...

and the Mode / SWR 4 pole switch layout of a 148...

​

It is best to do a continuity check.,

Start by checking continuity at TP7 and 8 routing back to the posts back at the Power Choke, look at your traces, you'll find a wire from there that goes to the front panel - THERE IS YOUR COMMON at the MODE switch.

The Power Choke provides a Separate POWER supply which then supplies Pin 1 Audio Chip, and R193 - it shows continuity, now you know where the R193 leads are, then trace OTHER SIDE of R193 back to a wire that goes to the front panel to MODE switch - this is your AM REGULATOR output - ties to COMMON back to Power Chokes TP7 and TP8.

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

First question, what’s the “power choke”?
Voltage at tr42 emitter/41 base is 6.4 volts. Voltage at tr42 base is 6.8 volts. However! Both are variable as you adjust VR10. I can adjust them by turning vr10 to get basically zero volts there to well over 8. Should those be adjustable in that manner?
If I lift the base pin of tr41 off the solder pad, it shows 6.2 volts and the pad shows 13.8.

 

[Brian G]

To help you both...

View attachment 44052
Also - looking at this link...
https://www.worldwidedx.com/threads/cobra-2000-help.261424/#post-758519


Which contains this...

and the Mode / SWR 4 pole switch layout of a 148...

​

It is best to do a continuity check.,

Start by checking continuity at TP7 and 8 routing back to the posts back at the Power Choke, look at your traces, you'll find a wire from there that goes to the front panel - THERE IS YOUR COMMON at the MODE switch.

The Power Choke provides a Separate POWER supply which then supplies Pin 1 Audio Chip, and R193 - it shows continuity, now you know where the R193 leads are, then trace OTHER SIDE of R193 back to a wire that goes to the front panel to MODE switch - this is your AM REGULATOR output - ties to COMMON back to Power Chokes TP7 and TP8.

Since rework always uses different Colors for wiring - the best way is to use the HARD WIRED routes of where the point to point continuity on the traces, locate open pads then resolder PROPERLY to connection points.

There is normal (13.8) volts at both pin 1 of IC chip and the "input" side of R193. The red wire coming off the other side of R193 that goes to the mode switch is also showing 13.8 which as I understand it, is to high?

Not 100% sure about the rest of your note in red though.

. Again I see the orange wire that come off the mode switch to TP 7 and 8 that looks like it is the power feed to those. However there is zero volts on that orange wire so there is zero at the test points.

 

[guitar_199]

Re-thinking this.........

First off.... yes.....that VR will change the bias conditions on TR42/TR41.....

And I just thought about something......

With the switch "in question" ... that means....even when your mode switch is in AM......TR41's emitter is FLOATING. THAT is why you are seeing 13.8 on the red wire.

With the emitter floating...... 0 current is flowing through TR41 OR the resistor strapped across it. With ZERO current flow..... neither TR41 or that resistor will be dropping any voltage..... therefore you WILL see 13.8v o the red wire.

We need to get that switch situation fixed!!!!!!!!!

 

[guitar_199]

Okay!!!! I am back to "this request".......

Can you get me a pic of your mode switch.......as STRAIGHT ON FROM THE BACK AND as CLOSE as you can possibly get it???

And..... are your soldering "chops" okay? You feel okay soldering on that switch???

 

[Brian G]

Re-thinking this.........

First off.... yes.....that VR will change the bias conditions on TR42/TR41.....

And I just thought about something......

With the switch "in question" ... that means....even when your mode switch is in AM......TR41's emitter is FLOATING. THAT is why you are seeing 13.8 on the red wire.

With the emitter floating...... 0 current is flowing through TR41 OR the resistor strapped across it. With ZERO current flow..... neither TR41 or that resistor will be dropping any voltage..... therefore you WILL see 13.8v o the red wire.

We need to get that switch situation fixed!!!!!!!!!

I do think the switch is bad and at the end of the day, that will be proven the source of most of the problems. I did order a new one (per Nomad's post) from ebay but it is coming from China (boo!) and won't be here for weeks. I think that will be next test unless there is another reason why the orange wire is not showing any voltage and therefore none at the test points....

 

[guitar_199]

Okay, if you have ordered one.... I'll drop it.
I was hoping that we could find one of the spare switch sections and move the white/red/green/orange wires to the right pins on the unused switch section...and it would just work. That way you could get around having to buy another switch.

So anyway... you DID find a source for that switch?????

 

[Brian G]

Okay, if you have ordered one.... I'll drop it.
I was hoping that we could find one of the spare switch sections and move the white/red/green/orange wires to the right pins on the unused switch section...and it would just work. That way you could get around having to buy another switch.

So anyway... you DID find a source for that switch?????

Yeah, nomad had a link for it on Ebay. Looked right but we will see. I just didn't want to mess with the current one. Are you agreeing it is a good bet the switch is bad? I just don't see any other reason orange wire is not providing the 13 volts to the test points since it originates at the mode switch to the test points. That seems to be main issue at the moment....I need to fix this problem before I go back to the original problem (from other threads) about no RF power out.

 

[guitar_199]

Oh YEAH! I really do think that switch section is toast!!!!
And you say that the original problem was NO RF OUT?
I am wondering if, once you get the switch working, you WILL have RF out!!!!!

This would certainly stop it! This switch section that you are fighting is how your driver and final get their "power"!

 

[Brian G]

Oh YEAH! I really do think that switch section is toast!!!!
And you say that the original problem was NO RF OUT?
I am wondering if, once you get the switch working, you WILL have RF out!!!!!

This would certainly stop it! This switch section that you are fighting is how your driver and final get their "power"!

I agree. I think in the end I may find that was the source of my all my issues with this radio. We will see.... Once I get it in and installed I will be back on to update you!

If anyone has any other things to check in the meantime, let me know...
Thanks for all the help.

 

[Handy Andy]

First question, what’s the “power choke”?

I keep forgetting...

You're on a 2000, the Power Choke is that big power supply transformer...



You have a big empty space where the MOBILE version of this board uses the POWER CHOKE in part of the Power supply filter the 148 uses.

IN a 148 this is what it looks like - by AM Regulator.

I did not realize that some BASE radios don't have this Power Choke.
Then I remembered the work I did to the ones I repaired at the shop.
They had power Chokes in them, because they were set up to use a external
power supply to handle a separate amp but they (owners) installed a
power choke to lighten the load (Filter) off the Amps power supply.​

SIGH - My bad...
​