Cobra 2000 barely any transmit power going out ???

[FlyBoy50]

Around a week ago I noticed my Cobra 2000 barely moving the power needle on my SWR meter when I keyed the mic. ( tried several mics ) The transmit light lights up on the Cobra and if I talk to my test radio in the other room I can hear it receive the transmit from the Cobra but with no authority. So I decided to try the radio on my kitchen test set-up. Same thing on that meter, it barely moves the needle on that meter, and yes on AM ! So what is the probable cause and a approximate cost to fix. I could make a 3.5-4 hour trip to DTB Radio for a fix but at my age I'm not crazy about the idea of that and shipping it is a flat out NO NO. That's why I've been buying new radios because I knew this day would come. I haven't opened the radio up yet but that is next. Anybody got any ideas ! HELP Please PS. Dave at DTB Radio is a great guy and my Ace in the hole if need be.

 

[nomadradio]

Did you try to transmit in AM and sideband both?

73

 

[Onelasttime]

Has the radio been recapped yet? Have you checked the input voltage from the internal power supply? Have you checked the final?

 

[Ghetto]

If you can hear it on the other radio chances are the pre driver/driver is working and the final is blown or final bias circuit problem. Could be an easy fix if it was just the final.

 

[FlyBoy50]

Did you try to transmit in AM and sideband both?

73

It's the same way on sideband. And I bought it off of ebay a couple years ago so I don't know the radio history but everything worked fine except 1 meter light which I fixed. And I laughed because when I got it I didn't know it had extra channels until I stumbled on to a couple repurposed switches. And it's been a good radio up until now but that is to be expected with something that old. That why a old mechanical mechanic like me decided to buy some new radios. Thanks for your help !

 

[9C1Driver]

If you have a trusted shop that close it would be pretty easy to ship it to them. Just double box it and use those foam peanuts.

 

[BayouRadioAmplifier]

just looked at DTB Radio website.
This is funny that he posted:

Due to issues with RCI quality issues we no longer
stock or recommend any RCI products. We will still
do special orders.

---------------------------------------------

I like working on them RCI / Galaxy radios.
I have a 2950 and two Galaxy Saturn's to work
on today. Fun, fun, fun, except for the circuit
board damages around the RF output section.

But,

A few weeks ago, I had a 2000 doing the same thing.
It had weak, less than half a watt of RF output.
It was worked on before by somebody, a few times.
Around the TR39 pre-driver transistor there is circuit
board damage, and other bad soldering around
the RF driver and final. The problem here turned out
to be that capacitor C163 was bad. Just an example
here, and hopefully you can find someone that can
probe around with a scope, to find the problem,
and not just "try this" and "try that" and do a bad
job of soldering, causing damage to the circuit
board. I get this quite often.

 

[FlyBoy50]

If you have a trusted shop that close it would be pretty easy to ship it to them. Just double box it and use those foam peanuts.

Thanks for the info and it is some thing to consider. Shipping a radio is almost like playing Russian Roulette with the gorilla baggage handlers, but it is tempting to ship down and pick up for the return ride. I might open it up and look for a No Brainer Obvious problem. Not often but some times a Man Gets Lucky. Then I could sell it and end of problem. LOL

 

[nomadradio]

Ditch the peanuts. Bubble sheet is the way to go. The large 3/4-inch bubbles are best for a radio. A two-inch (or more) layer of bubble on all six sides of a radio will protect it from most hazards so long as they don't rip the carton open. And a double-boxed radio is mostly protected even from that.

Just ditch the peanuts. They settle out and leave empty space inside the carton. Never leave room for a radio to move around the tiniest bit. Any empty space inside the carton invites impact damage if it can rattle around inside. Bubble sheet won't shift around and let the radio rub against the inside of the carton.

73

 

[FlyBoy50]

Ditch the peanuts. Bubble sheet is the way to go. The large 3/4-inch bubbles are best for a radio. A two-inch (or more) layer of bubble on all six sides of a radio will protect it from most hazards so long as they don't rip the carton open. And a double-boxed radio is mostly protected even from that.

Just ditch the peanuts. They settle out and leave empty space inside the carton. Never leave room for a radio to move around the tiniest bit. Any empty space inside the carton invites impact damage if it can rattle around inside. Bubble sheet won't shift around and let the radio rub against the inside of the carton.

73

That's one thing I do is save packing material from previous shipments and some sturdy boxes. Right now I have more important items on my plate but it will be like a wife that I don't have. Nag Nag Nag ! LOL

 

[loosecannon]

most likely the final or it's associated bias diode are bad, but that's just guessing.

if you want to try installing a final you can get one here:

2SC1969C HG

stores.goldeneagleradios.com

you can also remove both the final and the bias diode (thing that bolts to the front of the final transistor) and test them.

you can find tutorials on YT.

im not sure where to find the bias diodes these days.
maybe someone else knows.
LC

 

[nomadradio]

The bias diode in a Cobra 2000 almost never goes bad, unless it gets a lightning surge or something equally violent. The bias diode isn't connected directly to the final transistor's base circuit like so many radios made by RCI. There is a NPN buffer transistor between the bias diode and the final transistor's base circuit. The buffer transistor generally protects the bias diode when a final transistor croaks. A radio that connects the bias diode directly to the final's base circuit makes the bias diode a potential surge victim when a final fails.

73