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Cobra 140 gtl tx/rx meter replacement

red97k1500

Well-Known Member
Nov 26, 2012
359
293
73
texas
i am restoring a cobra 140 gtl that I bought on eBay for less than 50 dollars shipped to my door..... I own 5 uniden pc385 boarded radios all mobile versions, I bought a cobra 25 replacement meter off eBay, and it does not work. I Naively thought all cb radio metors were the same.... but I am wrong without a doubt.

If anybody knows from experience, please tell me which replacement meter to order off eBay for a cobra 140 gtl please.

Doing it through trail and error is to expensive
Considering they cos between 10-12 dollars apiece.
 

Well I contacted an eBay seller, and he claims that a cobra 25 meter will work in a cobra 140 gtl... maybe I just got a bad one? He also stated that cobra 25 29 and 148 gtl Meters are all the same. Any body know this to be true?
 
I know the 25's used to be common cathode, but are common anode now. The sellers claim can't be true, therefore he may be wrong about the 140 also.

I'd guess the 140 is common cathode if the 25 meter didn't work.
 
Thanks... that’s one of the reasons I wanted to use a 25 meter is because it does not have an swr cal on it.... I know there is a + and - and I hooked it up just the same as the old one even tried tweaking the vr adjustments, it didn’t help I think I just got a bad one
 
Is vr1 the only adjustment for the S meter in a pc385 radio. It seems to have more affect on am.... my S meter reads different on all three modes. It’s reading to high on side band, I’m hoping there’s another adjustment to lower the S meter on lsb.
 
it has been about 4 years since I worked on one. check VR10 and see what it does. that is all that comes to mind for the s meter for SSB.

never mind VR10 is the power meter.. only shows VR1 for the s meter on my manual.
 
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I have vr1 all the way down... I wonder if there’s a way to modify a circuit,to lower it more like changing out a resistor.
 
after thinking about this radio with SSB signal acting up.
are you testing the meter on a dummy load so it does not have a signal coming in? if you are and the needle moves up you may have some harmonics going on in the SSB modes. let us know if you are testing it with a dummy load or on a antenna.
as old as the radio it may be time to recap it. a cap can cause the problems you are having.
 
it has been about 4 years since I worked on one. check VR10 and see what it does. that is all that comes to mind for the s meter for SSB.

never mind VR10 is the power meter.. only shows VR1 for the s meter on my manual.
Actually, VR10 would be for RF output meter there is only one adjustment for the S meter which is VR1. IF there is an issue with the meter movement you may want to test the amount voltage being delivered to TR12 essentially this is the meter driver biased by a signal from L3 so I don't know what you have for equipment but a meter capable of reading very small signals would be helpful even a scope which is what I would be inclined to use. I don't know what kind of equipment you may have but if you test the meters with DVM on an ohms scale you should be able to see significant meter movement. It's not impossible to have several meters that are bad just not likely. I'm inclined to believe there are issues with something in the line feeding the meter driver you may try adjusting L3 just take note where it is and slowly adjust but you would need a signal to try this like I said I don't know what you have at your disposal.
 
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Ok thanks every body for the info.... the radio in question is the old pc385 boarded president Mckinley.... in the last month I have recapped the radio using all new nichicon electrolytic capacitors... I think I changed 32 of those... and I also changed every tantalum capacitor 11 or 12 of them.... My test equipment consists of a 35 dollar dvom, a 50 ohm mfj dummy load, and a radio shack swr/ watt meter. I do not own a scope or a signal generator. And I have been testing it on a dummy load and an antenna.... even when connected to my dummy load It shows s3 on lsb.....

Let me give y’all the whole story... the receive has seemed a little low on this radio since I have owned it, I would have to have the volume 3/4 the way up to hear people good.so on Saturday I drove two hours one way to take it to a tech for an alignment...

told him about the issue with the volume, and that I had recently recaped the radio and would like a full transceiver alignment. He said the tx side was fine, and did not need to be messed with... so he did a receive alignment.... he also added a 1 micro farad capacitor on the solder side of the board to the emitter of tr36...this brought the recieve way up, now I only need to turn the volume 1/4 the way up, like my other pc385 radios. I have tried lifting a leg of this capacitor and it does not fix the S meter... whatever the receive alignment is that he did pegged my S meter... I mentioned this to him while the radio was still on his bench, he assured me the area his shop is in just has a lot of noise... so I just assumed he has s9 of noise in this area.... the alignment did help the receive, the radio sounds just fine to me, and still gets good audio reports.... the only thing it seems to have messed up is the S meter. The S meter was pegged all the time I’m just trying to match it to what my bone stock cobra 140 gtl’s S meter does.

Thanks for any help y’all can give me
 
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are you saying you still have a s meter reading. sounds like the alignment may be off some. see what the other guys think.
 
Yes when hooked to a dummy load I still have an S meter reading of about s3 on lsb... if I switch to am no S meter reading at all... if I switch to usb on dummy load s2 on meter.
 
S-meter reading on sideband receive suggests the carrier oscillator isn't set right. Should be 7.8025 on USB, 7.7975 on LSB and 7.800 on AM transmit.

The shaft inside the trimmer capacitor for those two crystals can oxidize and shift those crystals off frequency after a few decades.

73
 

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