COBRA 142GTL

[KD2GOE]

I am working on my friends cobra 142 GTL and I need to fined what parts and transistors to look at to fix the AGC on the radio. I am in NY and I get people all over that are putting out a lot of power they sound the same on this 142GTL as my uniden Washington. but people putting out "stock power" that are 12 miles away don't even move the meter vary much..

so I am guessing some thing is not right with the AGC... there was a few transistors that I found that where dead I replaced from a parts cobra 29 I got it this far... but I don't want to blindly swop every transistor..



here is a video if it helps

http://www.youtube.com/watch?v=Qytbfz9xfag&feature=youtu.be

 

[Robb]

I'm sorry; I don't see an issue here.

BTW - do you just 'blindly swap' transistors; or do you bother to just take them out and test them at all?

 

[KD2GOE]

Well I guess it is not apparent in the video but the reseave is low and and only the real strong singles are making it wile the weeker ones are soft and don't move the metter like my uniden..


Yes I did test the transistors but u have to take them all out to test them... I am not "blindly swapping" transistor's the ones that where bad where TR9, TR10


Who ever worked on this radio befor my friend got it put china driver and finals in as well.. I put a NOS driver in and a eleflow cb-20 in...

 

[melaza]

:thumbdown:

 

[Robb]

Well I guess it is not apparent in the video but the reseave is low and and only the real strong singles are making it wile the weeker ones are soft and don't move the metter like my uniden..


Yes I did test the transistors but u have to take them all out to test them... I am not "blindly swapping" transistor's the ones that where bad where TR9, TR10


Who ever worked on this radio befor my friend got it put china driver and finals in as well.. I put a NOS driver in and a eleflow cb-20 in...

Doesn't mean that there is a part failure here. That could be the result of a receiver that is slightly out of tune/alignment. If there was a problem with the AGC; then all signals would be loud and others louder and distorted. I don't see that here - at all.

Some signals should be weak on the S-meter. If there wasn't a variation, then I would be concerned. Not all signals that reach a radio are equal by any means. They are anything but equal.

 

[KD2GOE]

Doesn't mean that there is a part failure here. That could be the result of a receiver that is slightly out of tune/alignment. If there was a problem with the AGC; then all signals would be loud and others louder and distorted. I don't see that here - at all.

Some signals should be weak on the S-meter. If there wasn't a variation, then I would be concerned. Not all signals that reach a radio are equal by any means. They are anything but equal.

I did go through the tune/alignment it helped a lot but it still is not right...

 

[Robb]

Re-aligning the receive portion of a radio is probably the toughest part to do right. It also requires a lot of experience and expensive gear. It is safe to say that unless you have both, then that could be problematic.

I use a Hp 8656B Sig/gen and a SINAD meter. The tuning procedure is not anywhere as simple as the Service Manual makes it out to be. That has been my experience.

 

[sonoma]

you could even have a lazy s meter. it may not be responding to low signals very well due to age. the VR could be weak causing low meter readings also.

 

[KD2GOE]

Re-aligning the receive portion of a radio is probably the toughest part to do right. It also requires a lot of experience and expensive gear. It is safe to say that unless you have both, then that could be problematic.

I use a Hp 8656B Sig/gen and a SINAD meter. The procedure is not anywhere as simple as the Service Manual makes it out to be. That has been my experience.

I have neather but I am counting this as radio shop 101. And hope to save up to get some gear to do this... Right now I am poking along "wife lost her job" but when she get a new job I can start saving up...

 

[MR_Frequency]

I have a 142 that was doing the exact same thing. Its as if the signal is getting held up somewhere. It it is working, I just know the radio should have better ears. I have put new meters in as well as all the electrolytic caps, several transistors, including tr 9 and 10 as mentioned in this thread and any germanium (if I got that right) diodes too. New 8 pin regulator ic and audio amp and finals and its still not right. My friend has the proper alignment gear and we have gone through the alignment step by step per the sams photo fact and still its not quite right. It is working much better than when I first turned her on after 13 years in a box.

 

[sonoma]

the only thing I see feeding the S meter is VR10, D48 and D49 , c146 and c147. if the receive is adjusted properly as Robb mentioned this is a start for thr main parts to look at in line with the S meter.