Cobra 29 ltd classic TX issues

[abitrulez]

i had a blown final replaced it and the rf driver keys up fine then after you start talking for a few the lights dim and the needle will fall back with backwards modulation unkey key back up talk and it does it again now i have replaced the volt reg, changed some elect caps but still have the problem i checked voltage at jp36 and it starts going crazy anybody have any ideas? audio ic seems fine

 

[bandaid kid]

What is the SWR on the antenna? High SWR can cause the radio to shut down on transmit.

 

[abitrulez]

What is the SWR on the antenna? High SWR can cause the radio to shut down on transmit.

i am usin a dummy load, this is being tested on the bench

 

[bandaid kid]

Okay! Good luck with it. I have no ideas to give you. I was thinking that the dimming was SWR related but it's not. I'll think some about it.

73

 

[nomadradio]

Ummm. Bad power switch?

Don't see it too often, but checking voltage on first one, then the other lug on the power switch would reveal this in a hurry. Or, if bridging across them with a probe tip makes everything come back to life, that's the trouble.

73

 

[abitrulez]

Ummm. Bad power switch?

Don't see it too often, but checking voltage on first one, then the other lug on the power switch would reveal this in a hurry. Or, if bridging across them with a probe tip makes everything come back to life, that's the trouble.

73

i tried that and still the same it evens dims the light on my powersupply when this happens i thought maybe thermal short,
but nothing is out of norm for the temp. i have tried two new sets of finals and drivers still the same after a few keyups with audio then it has a load on it crazy thing i have ever seen..also changed out audio ic

 

[DTB Radio]

If its dimming the supply, then there has to be a short somewhere. hook up a current meter to check for current hgher than about 2-3 amps when transmitting. Also, check the supply voltage at the power supply itself when this happens. You might have a faulty supply.