Cobra 200 GTX DX

Owch. Could that have been a 200 GTL DX instead of GTX DX? I'm not familiar with the model number given.
The model I suggest was the higher power foray that Cobra tried to make into the world of an actual 10 meter ham rig instead of a CB radio, but even at its best it suffered from underrated parts and a badly unstable SSB signal. But a lot of loyal users like them for the higher power as an AM radio after a simple conversion to CB.
You didn't mention whether it was the power lead or the antenna that your friend had hooked up wrong, but since it's dead now, either a backwards DC cable with a really big fuse, or the wrong antenna with a long key-down time, will have killed the final transistors. There are actually two, and the original ones ceased to be available in 2006. The replacements are in shorter and shorter supply, and must be replaced as a pair, even if only one is shot. A pair from one of the big distributors goes for $149.80 (dealer cost), plus shipping, plus the accessory parts that get replaced with them, plus bench time, and any other parts, etc. If it was the DC line that got reversed, add in the cost of an audio chip, several electrolytic capacitors, etc.
Unless that particular radio had been dipped in gold and hand delivered by cherubs from one of Michelangelo's paintings, it would probably take a qualified tech under ten minutes to determine that this poor Cobra's repair costs would exceed replacement with a more modern and reliable product.
Some older radios that have had similar catastrophic occurrences like this one has can be uncomfortable to repair, as a tech has to always wonder if he's caught every single component that was stressed *just short* of failure before he sends it out the door, only to have it start showing up again every month or two for a warranty re-work.
Sorry to be so wordy, especially with such bleakness. Sometimes it's easier & faster to just open up the case screws in front of the customer and let him see the charred parts and carbon tracks and let them speak for themselves.
But maybe the protection diode did its job, your friend stopped when the small fuse in the red wire blew, and no harm was done, and it will only be a 15-minute fix.
Hope springs eternal.
73,
Handlebar

 

Lucky man indeed. There's a small diode just inside the radio that's placed "backwards" across the power terminals, so that if someone hooks up the power reversed, that diode shorts out (and stays that way), and blows the fuse in the power lead. As long as the user doesn't pull the all-too-often of putting in bigger and bigger fuses until he finds a value that *doesn't* blow, and just stops right then and there like your buddy apparently did, all that's needed is to replace the little replacement diode inside and the power lead's fuse.
That sound you hear is the bullet he dodged
I'm glad it worked out OK for him. Thanks for the update, too. I was worried it was going to become a doorstop from the original description of what went wrong, and what all too often happens before they finally get taken in to a shop.
Well, it's 3am local here, so I guess it's time to close up the bench and go see if that Guinness is cold yet.
Cheers & 73,
Handlebar

 

toss out that cobra 200, Nothing but junk, JMO

 

Grouch,
I've never had any Tram gear myself, but have had a few go over the bench over the years. It's kinda neat that, even though none of this stuff that was built 30 or 40 years ago was expected to last even 20 years, a lot of it is still chugging merrily along. And a lot of it is doing it without any help; go figure!
Right now I've refurbishing 3 old Hammarlund "boatanchor" receivers built between 1959 & 1962. Only one had had any parts replaced before it came to me; two of them were working when they arrived. They both need some parts replaced just on general principles, but it's still amazing that they work.
Uniden has usually had a good manufacturing stream. The same factory that made their stuff for years also made a mid-tier commercial two-way product sold around the world.
I think a lot of it can be chalked up to how stuff is treated. You're apparently better with your stuff than a lot of folks are.
73,
Handlebar