My problem with this radio is that it's rx is fine,but when i try to key up the led light goes out(no red).I've checked the pa with an external speaker and no modulation.The weird thing is if you look close enough to the led it try's to change to red when you key up?.No dead key carrier at all,could it possibly be the audio chip?,any help here guy's. bigun :? (p.s)yes the mike is good,i think it's in the audio section around the audio chip)
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
cobra 29 ltd nw classic
- Thread starter bigun297
- Start date
bigun297 said:
IM fairly sure that you would get audio out the PA if the audio chip was good , but your also saying there's no dead key , which I think your assuming no power being transmitted ? Anything different happen before you noticed all of this ? I've seen some pretty weird things in my time , could you have hooked it up backwards maybe ? I've seen protect diodes go to the point where they would still fire up the radio but nothing else , and if you were to look at them , they would still look good to the naked eye when in reality they were dead. Good luck to you 297
Check your mic first... sounds like the radio is not keying.
First thing to try is to jump the tx and ground pins on the mic jack.... ground is pin 1.... tx is pin 3... they are diagnal from each other. Anyhow take a screwdriver or anything you have to jump these 2 pins together..... when these 2 pins are connected the radio will "key".... you should see the tx light come on and you should see carrier (deadkey) power on the rf meter.
The fact that the light is flickering or "trying to come on" makes it seem like there is an intermittant connection in the mic.
If you had carrier power showing on the meter BUT had no swing with the TX light on... then you would switch to PA mode to check the audio amp out.
But because you have no carrier and the tx light isn't coming on ( or its slightly flickering) is basically showing you that the radio isn't keying or going into tx mode. If the switching in the mic isn't working in cb mode, it won't work in PA mode either.
No carrier and no tx light is a big hint the radio isn't keying.
Easiest way to check this is to jump the tx pin to ground and see if the radio keys ( tx light comes on) and you get carrier power. If you get carrier and a tx light you have a bad mic.
Most of the time keying problems are mic related.
Good luck..... take care
First thing to try is to jump the tx and ground pins on the mic jack.... ground is pin 1.... tx is pin 3... they are diagnal from each other. Anyhow take a screwdriver or anything you have to jump these 2 pins together..... when these 2 pins are connected the radio will "key".... you should see the tx light come on and you should see carrier (deadkey) power on the rf meter.
The fact that the light is flickering or "trying to come on" makes it seem like there is an intermittant connection in the mic.
If you had carrier power showing on the meter BUT had no swing with the TX light on... then you would switch to PA mode to check the audio amp out.
But because you have no carrier and the tx light isn't coming on ( or its slightly flickering) is basically showing you that the radio isn't keying or going into tx mode. If the switching in the mic isn't working in cb mode, it won't work in PA mode either.
No carrier and no tx light is a big hint the radio isn't keying.
Easiest way to check this is to jump the tx pin to ground and see if the radio keys ( tx light comes on) and you get carrier power. If you get carrier and a tx light you have a bad mic.
Most of the time keying problems are mic related.
Good luck..... take care
If you rule out intermittent connections, then its liekly a shorted cap or problem with the 8-volt regulator ciruit (power transistor in the middle of teh board near the mic jack). Touch up the solder joints near that transistor and see what happens. If no change, replace it and see what you get. If that doesn't do it, its schematic time
cobra 29 nw classic
Ok! i jumped the pins just to make myself happy that it was'nt the mike.No key up or red led,thnx for the info dtb i'll check it out tomorrow.I have plenty of old cobras laying around for parts,it's very possible it's the 8volt regulater and i'll look under the microscope for burnt traces also in that area.Question! what will the caps look like if they are bad,black?,oily looking,darkish brown mabe?. bigun :?:
Ok! i jumped the pins just to make myself happy that it was'nt the mike.No key up or red led,thnx for the info dtb i'll check it out tomorrow.I have plenty of old cobras laying around for parts,it's very possible it's the 8volt regulater and i'll look under the microscope for burnt traces also in that area.Question! what will the caps look like if they are bad,black?,oily looking,darkish brown mabe?. bigun :?:
The caps may not look any different, and probably wont look any different. Thats where a schematic and proper test equipment come into play. You will need a voltmeter at least to check each power supply voltage on the schematic. the SAMS manual is best, #117. its close enough to the newer 29's to work for you if you're careful.
- No one is chatting at the moment.
-
-
-
@ BJ radionut:
Discord - A New Way to Chat with Friends & Communities
Discord is the easiest way to communicate over voice, video, and text. Chat, hang out, and stay close with your friends and communities.discord.com
-
-
