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Cobra 29 unstable dead key
- Thread starter Illahe
- Start date
Unsure if it will help, but maybe heat related? Possibly a cold solder joint somewhere? Gently push around the board with a plastic tool when it happens to see if the deadkey watts jump back up... Just an idea to try. 
Otherwise, hoping its not something else more severe.
Otherwise, hoping its not something else more severe.
Now that I think about it, My Galaxy 99v does randomly drop power... Comes back randomly. I did try to poke around the board, but it was still acting up. I will need to take a much closer look at each solder joint.
Another Uniden PC66XL radio I bought at auction for a couple dollars wasnt working. It wasnt until one particular solder joint looked a bit off, and after adding a little more solder, receive came in nice and loud. I fixed a couple more PC66XL radios like this.
Another Uniden PC66XL radio I bought at auction for a couple dollars wasnt working. It wasnt until one particular solder joint looked a bit off, and after adding a little more solder, receive came in nice and loud. I fixed a couple more PC66XL radios like this.
You will want to document signal levels at different points in the transmit circuit chain when the radio is operating properly, then compare them to the ones you see when it falls off. This should narrow the problem down quite a bit.
I just had a Cobra 1000 that has a similar main board in it
with your same problem, then the RF out quit completely.
the problem was a burnt-out resistor R49 that
goes in line with the modulated voltage to the RF driver.
But I see on the 29's it does not have that resistor there.
and I just noticed on these 29 schematics they show a 1N4148
diode at D8. that must be a mistake. should be a 1N4001 type.
on many radios this diode is bypassed, to get that extra .7 volt
positive modulation swing.
check diode D8. key up radio. monitor the voltage at
the cathode side for about 12 to 13 volts.
with your same problem, then the RF out quit completely.
the problem was a burnt-out resistor R49 that
goes in line with the modulated voltage to the RF driver.
But I see on the 29's it does not have that resistor there.
and I just noticed on these 29 schematics they show a 1N4148
diode at D8. that must be a mistake. should be a 1N4001 type.
on many radios this diode is bypassed, to get that extra .7 volt
positive modulation swing.
check diode D8. key up radio. monitor the voltage at
the cathode side for about 12 to 13 volts.