Another abused Cobra 2000 brought back...

[Hawkeye351]

Got another Cobra 2000 that was abused brought back to life.

Before:
AM - deadkey 7w, swing to 10w peak, swing backward to 4.5w in average.
SSB - 10w peak.

Homemade channel board checked out. Seems as though it doesn't leak emissions or RF, seems stable. Screwy clarifier mod.

Now:
AM - 2.5w deadkey, swings to 14w peak, swings forward up to 7w in average.
SSB - 15w peak.
All issues fixed.

Keep them old girls coming my way, I gotcha on a 2000.

Thanks to all the knowledgeable people on this site for helping me get this far.

 

[guitar_199]

This is a "noble quest". Keep up the good work!!!!!

 

[Hawkeye351]

The purple wires are for a variable key.
The red meter lights I still have to replace.

Thank you for the compliment....

 

[Hawkeye351]

What has been done previously that the owner wanted left in it:

Passthrough regulator changed to an NTE-152.

Final replaced with an NTE-236.

R131 clipped.

Homemade channel board installed.

What I did (I do the same with all 2000s):

Replaced the 10v blues caps.

Checked tolerance of all other caps (all barely in tolerance but still good).

Checked all IC and transistor voltages.

Replaced R126 and R124 (someone placed 1k ohms in those spots, factory is usually 10k ohm), with 5.1k ohm resistors.

Replaced C109 (10uf) with a 4.7uf 25v.

Replaced C18 (330uf) with a 470uf 35v.

Reset bias.

Realigned entire radio.

Tuned the output.

I know many may frown on changing R124 and R126 out for lower values, but I've had great success at 5.1k ohms with no breakdowns or heating issues, and the signal still remains somewhat clean. And again, I would have put R131 back together but the owner said he wants it to stay like that.

I've been told several times by Cobra 2000 owners, after they got their radios back from me, that their radio never drove their amps the way they do now, lol... The drive these radios can produce does not come from power mods/swing mods/etc ... The drive comes from the alignment, plain and simple.

The VCO voltage coming from the VCO, the VCO buffer(s) and the oscillators are the key to making a radio drive an amp, it's where the gain comes from.

In short, (this info is for anyone wanting to redo their 2000 the same way):

Replace all the "10v blues" caps.

Replace passthrough regulator (1419 or 1135) with a 6487G. Also replace the regulator (1419 or 1135) on the power supply board with a 6487G.

Replace C18 with a 470uf 35v up to 1000uf 35v.

Replace C109 (AMC Timing capacitor) (10uf) with a 4.7uf 25v.

Replace R124 and R126 (10k's) with 5.1k ohm resistors.

Replace R228 (560 ohm) to a 1.2k ohm.

Lift rear leg of R228 up from board and solder the unbanded end of a 1N4001 diode to that lifted R228 leg, solder the banded end of that same diode into the empty hole left when you lifted the leg of R228.

Replace the limiter if it's been removed or disabled.

Make sure VCO voltage is adjusted properly.

Make sure VCO Buffer(s) are maxed out (this is where the audio sensitivity for receive and transmit comes from, which in turn produces more gain, more drive).

Make sure PLL offset oscillators are dead on frequency with clarifier control in the center position.

Make sure the carrier offset oscillators are "Zero-Beat" to a good quality ham rig as the transmit signal to zero beat to.

Adjust transmit frequency.

Adjust bias.

Adjust RF Stage.

Tune the output.

That is everything I do to a Cobra 2000, other than fixing issues.

 

[guitar_199]

Final replaced with an NTE-236.

A related question.

I just looked in the SAMS for the C-2000.

The schematic shows the final to be a 2SC1969

Does THIS MEAN that the NTE-236 is a workable replacement????

If so.... I think that would make this one of those "holy grail" things....

 

[Hawkeye351]

Yes, NTE-236 can be used in place of a 1969, 2312, etc...for a final.
Also, the NTE-235 can be used in place of a 1306, 2166, etc...for a driver.

1969 still has more gain than the 236 and 2312. I would rather have the 1969.

One more tip:
Around the pre-driver you will see a cluster of resistors, one of those resistors will be either a 10 ohm or 12 ohm. If it's a 10 ohm then leave it alone, if it's a 12 ohm then replace it with a 10 ohm. Some 2000s/148s came with 10 ohm in that location and some came with 12 ohm. This resistor controls the gain the driver receives from the pre-driver.

 

[guitar_199]

Yes, NTE-236 can be used in place of a 1969, 2312, etc...for a final.
Also, the NTE-235 can be used in place of a 1306, 2166, etc...for a driver.

1969 still has more gain than the 236 and 2312. I would rather have the 1969.

One more tip:
Around the pre-driver you will see a cluster of resistors, one of those resistors will be either a 10 ohm or 12 ohm. If it's a 10 ohm then leave it alone, if it's a 12 ohm then replace it with a 10 ohm. Some 2000s/148s came with 10 ohm in that location and some came with 12 ohm. This resistor controls the gain the driver receives from the pre-driver.

Thank you sir! I am collecting these notes!!!!!!

 

[Keto]

My Cobra 2000 has seen better days, It needs help but not sure how much?

 

[nomadradio]

It's the years and the miles, both. If it's a 1979 radio you'll most likely need to consider replacing all the electrolytic capacitors in the radio. Sometime after the 40-year mark they will randomly fail for no other reason than old age alone.

But a 1993 radio that was run 24/7 for 20 years may need the same treatment because of the mileage. Heat exposure also speeds up the eventual failure of electrolytic caps. The hottest part of the radio is inside the clock/counter shield. A radio with counter trouble that has to have all the caps inside that box changed will probably need the rest of them before too long.

The oldest 2000 will probably need a lot of love, unless it has only 500 original miles on it. And the newest one will as well, if the mileage is high enough.

73

 

[Woody-202]

In short, (this info is for anyone wanting to redo their 2000 the same way):

Replace all the "10v blues" caps.

If you went as far as replacing all the 10v blue caps, and the others were just barely in tolerance but checked "okay" I'd tell the customer he could run it with the just in tolerance caps but you recommended that they too should be replaced (after all, you're already in a prime position to replace 'em), and put the Yay or Nay on him.

( I'd just flip it with my head as if this were a car being inspected and tired were barely within limits - but passable).

Does he want to got through this again when it could have been done the last time it was in the shop, or cross-fingers and hope it makes it for another year or two. As a customer, I'd pick what was behind door number one - replace all of the barely in tolerance caps, because ultimately, it would be less expensive as you would have pointed out (we're at the point where we can start putting it back together or, because half the labor to get to this point has already been done, they'd save money and your time in doing it now or roll the dice).

As well, if one or two of those barely in tolerance caps went bad a few months later, and took out other components, you can just remind them it was their choice when it was in the shop earlier. I eventually had receipts printed like auto repair receipts: Items okay; Items in need of immediate replacement; and, items recommended to be replaced at the time of that visit. The customer would then pick A, B, or C, then circle their choice and sign the receipt (i got tired of some people trying to weasel out of things by saying something akin to: "Well, you never warned me about this - it's your fault".)

If they did have their receipt, or claimed it was lost, just pull out your copy.

My .02 cents

 

[Hawkeye351]

I don't do this as a business, it's only a hobby for me. Only money I make is for parts, supplies and gas because I pickup and deliver. I'm only helping these guys out until someone else comes along, because their decades old radio/amp tech passed away a year or so ago. I just share with others on here info that I feel may be of use for others that run into similar issues, if I did it for a business then I would have to neglect my other priorities in life, this is just a hobby. And I haven't had a complaint as of yet, thanks to a lot of others on this site that offers great info in issues I may run across.

I look at it like this,
I didn't pay anything to learn this,
I didn't attend any electronics courses,
The info I gather is offered freely to all,
So why should I get rich off my friends in their time of need? I can't take advantage of others.