Cobra 148 GTL w/RFX95HD

[Hawkeye351]

Got a return Cobra 148 GTL that I previously installed an RFX95HD on up on the desk today.

Issue:
Owner got long winded on it the first night he had it, and the amp got so hot that it wouldn't key up anymore. The power started fading from 110w down to nothing.

Evaluation:
Although it ran scorching hot, the amp still works perfect, it just needed to cool down.

After running it a bit, I decided to flip the amp off and run barefoot. Well, we have no output whatsoever barefoot, sidebands or AM, nothing. All I did to disengage the amp was removed the 8v transmit only wire and ran to a spst switch. I have the fan on another spst switch. When I flip the amp switch to ON position, the output is around a 15w key and swings up to 110w PEP (45w average). When I flip the amp switch to OFF position to run barefoot, I have no output whatsoever on any mode. But, if I take the output wire off the so239 center pin and run a jumper from the so239 center pin to the spot on the board where the so239 center pin suppose to go and flip the amp switch to OFF position, then the radio will transmit barefoot.

I'm thinking he got it so hot that it damaged one of the relays in the amp or something else in the amp is shot.

Any ideas guys/gals?
He said he's fine with it always on.

 

[Shadetree Mechanic]

Sounds like the relay contacts are not making a good connection when it is off.

 

[Hawkeye351]

Sounds like the relay contacts are not making a good connection when it is off.

That's what I'm thinking also. I think it's due to his extended key down which got the amp scorching hot. The heat may have damaged the relay contacts.

10 minutes on the key, 2 minutes off the key, 15 to 20 minutes on the key, 2 to 5 minutes off the key. That went on for about 5 hours til his power started dropping, but he kept talking until it had no output cause it was so hot. He thought he blew it up, but I told him to just let it cool off a bit and it should go to working again, as I've noticed with these RFX95HD amps, they're pretty damn resilient, bounce back after output failure. But he wanted me to check it out anyway.

Note: when this happened, he had no fans on it or no way to keep the amp cool. I have fans on it now.

 

[Eldorado828]

With all the fets we're using, they keep getting bigger for more power and create more heat.... Another 10 years and we'll be having to have water pumps and radiators on our radios

 

[TM86]

With all the fets we're using, they keep getting bigger for more power and create more heat.... Another 10 years and we'll be having to have water pumps and radiators on our radios

Can't find it now, but there was a video of a guy who built a water cooling setup for his mobile radio installation.

 

[Eldorado828]

Can't find it now, but there was a video of a guy who built a water cooling setup for his mobile radio installation.

Yes it was a ranger 2970 series radio. He went wild with that build.

 

[Eldorado828]