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Old Cobra 29 LTD Sound Tracker No Receive until it warms up

Crossbow

Crossbow

Well-Known Member
Mar 25, 2016
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Anyone ever had a cobra 29 LTD Classic Sound tracker that would not receive until it warms up?

No matter what you do to it it will not receive until at least 4 or 5 min warm up time then it just pops on and will work the rest of the day with not problems.

This happens each and every morning when I turn it on. I have checked for cold solder joins and found nothing. You push on the board all you want or move things around in the circuit with no luck of it coming on until it warms up.

Thanks in advance for any help on this matter. About ready to take a hammer to it! LOL
 
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Well, I assume you mean that it also modulates on transmit if not let us know. If it modulates on transmit and can be heard on a speaker through the PA speaker "I know I didn't ask that" but you get the idea. So far it is limited to either not being heard on receive which if you had a radio or walkie talkie or something or a friend with a radio you may be able to see if the S meter is moving in unison with another radio being keyed while the 29 is in receive mode and this would indicate it is receiving but not getting to the audio section and would reduce the possible issues to isolated circuits. And this still could be electrolytic but I still like the process that narrows it down to the exact part at that time if you wish to replace all electrolytic as a preventative measure great. Now that is me I don't like replacing all the caps and not knowing the one that caused it. And it is possible to replace all caps only to find out that was not the issue I have had a few radios brought in and told all the caps were replaced so it can't be that only to find out they put a cap in wrong or even caused solder issues that didn't exist before Ok I have rambled on long enough.

(these tests would be handled on most workbenches all at once) but here we take care of them one at a time so bear with us.
 
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OldTech03 said:
Well, I assume you mean that it also modulates on transmit if not let us know. If it modulates on transmit and can be heard on a speaker through the PA speaker "I know I didn't ask that" but you get the idea. So far it is limited to either not being heard on receive which if you had a radio or walkie talkie or something or a friend with a radio you may be able to see if the S meter is moving in unison with another radio being keyed while the 29 is in receive mode and this would indicate it is receiving but not getting to the audio section and would reduce the possible issues to isolated circuits. And this still could be electrolytic but I still like the process that narrows it down to the exact part at that time if you wish to replace all electrolytic as a preventative measure great. Now that is me I don't like replacing all the caps and not knowing the one that caused it. And it is possible to replace all caps only to find out that was not the issue I have had a few radios brought in and told all the caps were replaced so it can't be that only to find out they put a cap in wrong or even caused solder issues that didn't exist before Ok I have rambled on long enough.

(these tests would be handled on most workbenches all at once) but here we take care of them one at a time so bear with us.
Click to expand...

Yes Sir the radio will talk fine when the RX is missing. PA works fine also.
The only thing that is not working is the receiving part until the radio sits on for like 3 to 5 mins then pops on and works fine all day until you turn it off for the evening.
Does not matter if there is an external speaker or the factory speaker.
The S meter will not show any RX as well until the RX comes back on.
In other words there is no RX at all until it warms up.
I have tested the S meter idea from using another radio on another bench to see if I could see any movement in the S meter or hear anything. It is dead!
 
1. PLL out of lock on RX.
Before butchering radio by recapping without reason tell me what is VCO voltage on ch40 when deaf and when OK?
2. Defective if filter might be a reason as well.
What is a voltage on output of 455(450)KHz filter when deaf and when OK?
This simple measurement will save stress, money and time. Radio as well.
Mike
 
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sp5it said:
1. PLL out of lock on RX.
Before butchering radio by recapping without reason tell me what is VCO voltage on ch40 when deaf and when OK?
2. Defective if filter might be a reason as well.
What is a voltage on output of 455(450)KHz filter when deaf and when OK?
This simple measurement will save stress, money and time. Radio as well.
Mike
Click to expand...

Mike, I will have to set it up and be ready to get those readings for ya in the morning when the radio is dead. Once it starts working it stays working until the power is taken away over night or many hours powerless I should say. I will try to get them before it comes alive. Only talking a few mins and BAM she pops on working.
 
You could even go back to good ole thermal troubleshooting, get you a can of canned air at WalMart they sell 3 in a pack for $14.95 if held upside down it will be freeze spray
use on an area that could be most likely to cause issue which seems to be only in receive section if it's transmitting on freq then it's not PLL related that confines it quite a bit. a very small sprit of cold may cause it to show up.
 
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nomadradio said:
I would also suggest switching the channel selector from channel 1 to channel 40 while it's "sleeping".

If it will receive on one or the other before the warmup period has passed, that would point to the VCO adjustment.

73
Click to expand...

Done ruled that out. Tried all 40 channels while its sleeping. Nothing happens.
The radio has been tuned to specs when it was working so I know it is not an adjustment problem.
 
nomadradio said:
I would also suggest switching the channel selector from channel 1 to channel 40 while it's "sleeping".

If it will receive on one or the other before the warmup period has passed, that would point to the VCO adjustment.

73
Click to expand...
Yes, I didn't think in that realm it's really a chore sometimes to remember all the variables/possibilities/things/stuff, thanks Nomad that could be relevant. I have an excuse I'm claiming amnesia.
 
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