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Cobra 2000GTL channel mod help

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Cobra 2000GTL channel mod help

Post by Tobin » Sunday, 25 February 2018, 13:25 PM

I have a Cobra 2000 GTL that was modified for extra channels (3 switch configuration) Now my radio is off frequency by pretty much one channel. All channels are one frequency too low. The modification works but the radio displays roughly one channel to low on all channels. The guy who modded the radio just used the online directions but he must have missed a step or two. the radio was on frequency before he modified the radio. The clarifier was unlocked I believe. I don't know if he locked it or not with his mod. I hope you can help. Thanks.
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Re: Cobra 2000GTL channel mod help

Post by MDYoungblood » Monday, 26 February 2018, 9:27 AM

Hello Tobin,

Welcome back. I moved your post to it's own topic because the problem your having is different than the topic you originally posted in.

Those switch mods usually make the radio go all over the place until you figure out the switch position configuration. If in regular CB position the channel is one off see if you can correct it using the clarifier, if you can then it's just a matter of having the radio aligned.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Monday, 26 February 2018, 11:23 AM

I can get the radio almost near the right frequency by turning the clarifier (both fine and Coarse) to the farthest point it can go one way. I think it is something else being the problem.
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Re: Cobra 2000GTL channel mod help

Post by MDYoungblood » Monday, 26 February 2018, 11:45 AM

Is one of the switches the 10kc mod, that would put it off one channel.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Monday, 26 February 2018, 14:41 PM

Honestly, the tech never explained anything to me but I can try and see if I can get the switch configuration to get it back on regular channel. Thanks for your help. i'll get back to you if you don't mind
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Re: Cobra 2000GTL channel mod help

Post by MDYoungblood » Monday, 26 February 2018, 15:23 PM

Yes let us know, you aren't the only one using that configuration. On Galaxy radios only 2 switches are used in a channel mod and a third is like I said, bumps the frequency up or down 10kc to get the skipped channels on the selector. There is also a lot of doubled and a couple tripled channels when flipping around. Best to make a map of how they work, luckily the 2000 has a freq counter/display. Start with regular CB 1 through 40, then switch one down, 1 through 40, switch one up - switch two down 1 through 40, etc..

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Monday, 26 February 2018, 17:26 PM

The radio has only two switches. The clarifer set to dead center on fine and coarse is exactly one channel below the channel readout. One switch seems to control the upper frequencies while the other switch just controls some frequencies below channel one. HELP!
Maybe I should be on channel 2 to get one with this mod but I don't think so.
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Re: Cobra 2000GTL channel mod help

Post by MDYoungblood » Monday, 26 February 2018, 17:50 PM

Okay,, in your initial post you said 3 switches. Is the frequency counter reading off as well? Sounds like an alignment is needed, most that do the mod don't have the proper equipment to realign the TX and RX. I'm wondering if he did the mod but never changed out the crystal.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Monday, 26 February 2018, 19:50 PM

The radio was originally modded when he received it for repair. he claimed he had to unmod the radio to service it. He never fixed anything. He then apparently remodded the radio and I picked it up after that. the radio has low TX and RX which was the original issue. Whatever he did when he remodded the radio, he caused the frequency to be off by exactly one channel no matter what position the switch is in. For example, 27.555 is on channel 25 with the switch engaged instead of channel 24. The second switch seems to find lower channels. I am very sure the proper crystal is installed. If I thought incorporating a third switch would fix it I'd give it a go but I have not seen any third switch configuration that will accomplish that.
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Re: Cobra 2000GTL channel mod help

Post by MDYoungblood » Tuesday, 27 February 2018, 8:55 AM

Are the regular CB channels reading right?

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Re: Cobra 2000GTL channel mod help

Post by sonoma » Tuesday, 27 February 2018, 10:41 AM

there is at least 3 or more versions of the channel mods and it changes where each one is at. are you looking at the proper channel chart for your radio mod. if need be I can give you links for 2 of them. the other I have on my hard drive. and I have seen one other mod in the past.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Tuesday, 27 February 2018, 11:41 AM

Please forward whatever information you can send. If you need an email, I can provide one.
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Tuesday, 27 February 2018, 12:43 PM

here is one version
http://www.cbtricks.com/members/cblinco ... ersion.gif
her is the 2nd version

http://www.cbtricks.com/members/cblinco ... rsion2.gif

if you will PM me your email I can send you the other files I have.
you never did say if the regular 40 11 meter channels are right or not. that would be a big help also

here is another site for the mod. not sure what the channels are on this one.

http://www.oocities.org/siliconvalley/p ... 8/8719.htm

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Tuesday, 27 February 2018, 15:36 PM

All bands are out by one channel my friend. Even the regular 40 channel band. I will send you a PM with my email. Thanks.
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Tuesday, 27 February 2018, 18:36 PM

you can pop the covers and see what pins of the PLL have been modded. this might help you see just what all has been done. you have about ever 8719 PLL mods I know of right now except for the last one I have not found as of yet. I believe the last one you could get 27.415 on the radio. most do not have that channel in most of the mods. I know I have it some where in my paper mods just have not found it as of yet. in fact it has been about 15 years since I remember doing that one mod. some of the locals here ran that channel and that was the last time I used it back then.
let me know if you were able to get the download. one of the mods I sent you shows what you have to do to get the 10KC mod. you can look at the PLL and see if it has been done

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Re: Cobra 2000GTL channel mod help

Post by sonoma » Thursday, 01 March 2018, 9:36 AM

Tobin have you ever figured out the channel mods as of yet. look at pin 16 I think it is . if it has a mod done to it would be the 10KC jump that mdy was talking about. should have a couple wires ran to it plus a resister across the cut trace if it has the mod done to it.
the last link I sent you above has the mod shown.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Thursday, 01 March 2018, 18:00 PM

I will have a look soon when I get a chance. Oddly, if it is modded that way then somebody forgot to put a switch there to disconnect the 10kc slide.
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Re: Cobra 2000GTL channel mod help

Post by Tobin » Thursday, 01 March 2018, 18:16 PM

I just looked at the underside and I see several connections to the PLL but nothing with a resistor. I sent some snaps to sonoma. I don't know how to send the snaps in here
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Thursday, 01 March 2018, 22:38 PM

Tobin, I looked at the pics you sent. looks like they used pins 10, 11 and 12. the board has so much flux on it I can not tell much about it. I would get some electronics cleaner for a circuit board and a tooth brush and clean the brown gunk off the board.
you have the the green jumper that I have no idea what it was used for unless it has a cut trace that I can not see they are repairing. can not tell if pin ten trace is cut or if it does not have to be cut. some had pin ten soldered to ground and some did not.
you have not verified if the radio has a 11.1125 or a 11.3258 crystal in place. if it has the 11.1125 crystal that will throw you down in freq's. the guy that did the mod for you have you talked to him about the radio being off freq? you said he had to unmod it for a repair then put the channels back in. since the guy must know some thing about radios to do the repair. I sure would be talking to him about it off freq.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Friday, 02 March 2018, 5:40 AM

The proper crystal is in the radio. I brought the radio back to the "TECH" and he was unable to put the radio back on frequency. Turns out, he is self taught possibly by trial and error and works mostly on PLL 858 radios. I will check the green jumper and possibly disconnect it and see what happens. I don't see a cut trace there just the same.
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Friday, 02 March 2018, 6:26 AM

verify what crystal is in the X3 spot by numbers. and what PLL is in the radio. they came with 2 different PLL's in them and one had to be changed out. some radios had the 11.3258 crystal and some the 11.1125 crystal and you had to pull the .1125 and install the .3258 in them.
also look at pin 10 and see if it has a solid trace to the PLL. if so it has to be cut to isolate it from the main board for the mods to work as it should.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Friday, 02 March 2018, 9:40 AM

I cleaned up the board as suggested and I decided to reflow some solder points that looked like they needed reflowing. When I turned on the radio it was back within reasonable frequency but it needs an alignment big time. This is way over my head but there is no decent technician with 500 miles of me that I know of and so I am slowly gonna try and get AM and SSB closer to the proper frequency. I am looking now for the alignment points but I am wishing I just could have a professional tech do it as is obvious. thanks for all your help so far. This radio has been off frequency a long time and finally I am making some headway.
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Re: Cobra 2000GTL channel mod help

Post by Tobin » Friday, 02 March 2018, 12:49 PM

sonoma wrote:
Friday, 02 March 2018, 6:26 AM
verify what crystal is in the X3 spot by numbers. and what PLL is in the radio. they came with 2 different PLL's in them and one had to be changed out. some radios had the 11.3258 crystal and some the 11.1125 crystal and you had to pull the .1125 and install the .3258 in them.
also look at pin 10 and see if it has a solid trace to the PLL. if so it has to be cut to isolate it from the main board for the mods to work as it should.
The crystal is 11.3258 and the PLL is 8719. Currently the radio frequency mod seems to be working just fine. Please see my recent post as I have got the radio back to regular frequency now but it needs an alignment now desperately.
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Friday, 02 March 2018, 13:23 PM

sounds like you are getting there.cleaning off all that goopy stuff and checking all those solder joints may get you up and running as it should. that stuff needs to be cleaned off after a few years so it does not mess up the solder pads.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Friday, 02 March 2018, 14:51 PM

Yes indeed, you have managed to figure out the issue that I had several people guessing at for about 3 years now. Congrats. Good call. As for the radio, she is in need of a good alignment now and I don't have the necessary skill. i am gonna try and see about getting somebody else to do that. i am only fooling things up more as my eyesight is not the greatest and poor lighting does not help
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Re: Cobra 2000GTL channel mod help

Post by sonoma » Friday, 02 March 2018, 15:18 PM

I see you show to be in Canada. hard to believe there is not some one here on the forum close to you since there is a lot of guy's on the site that live in Canada.

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Re: Cobra 2000GTL channel mod help

Post by Tobin » Friday, 02 March 2018, 22:02 PM

As luck would have it, Canada has a percentile of technicians percapita much less than that of the USA.
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