Hello everyone, i recently aquired a cobra 29 LX that had no output. Turns out the final transistor was cracked and a resistor was cooked. I replaced both components and the output came back. But when you modulate, it swings backwards and i cannot figure out why its doing this. Any help will be appreciated. Thanks in advance.
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Backwards Swing
- Thread starter CB RADIO FREQ
- Start date
What is it doing on the meter?? Chances are its set too high of a dead key.
Something is being over-driven, here. Are you running an amplifier? If so, reduce your dead-key to 2 watts or less.
I have run across this before but it is not always related to this problem, The meter diode, RF sense, may have been damaged from what ever happened to the final. Be sure to set the bias current and do not over modulate, approaching 90% is just fine.
73 mechanic
73 mechanic
I am not running an amplifier and on the meter it dead keys about 4 watts and swings back to about 2.5 watts. I am using a 15 amp power supply. I did find a diode that was burnt up (D8) and i replaced it but it did not effect anything. Im also not sure how to set the bias. Thanks
See if you can borrow a larger power supply just for a test. I've seen this symptom when the power supply just couldn't cut it.
use the 29LTD for tuneup. or use the ones off cobras site.
https://downloads.cobra.com/CB/Models/29-SERIES/
https://downloads.cobra.com/CB/Models/29-SERIES/
I have tried a 30 amp power supply but it still swings backwards. I do not think its a matter of a tune up as I have already tried the general tune up procedure.
Some good info here about what might be going on. Not so much in laymens terms, but hope it helps.
http://www.cbtricks.com/members/kd6tas/page4.htm
http://www.cbtricks.com/members/kd6tas/page4.htm
Check if dc volts at the final and driver are holding up under load, try turning down the modulation and see what happens.
Check if dc volts at the final and driver are holding up under load, try turning down the modulation and see what happens.
Ok everyone. I think I have narrowed it down to the adjustment slugs used to tune the radio in the tune up procedure. The adjustments are totally out of whack and I think it's causing to swing backwards. Does anyone know the factory settings for those adjustments?