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Cobra 146 Frequency Mod For Switch Kit and Others
- Thread starter CollinsMan
- Start date
I have a cobra 146gtl, realistic trc-453 in my nightmare pc 122 xl so if i fix the last one im going to get two more n Galaxy kit so far :headbang its very difficult. I have tried so many times already and i still can't do it
SWITCHKIT quotes:
Did you use the 27pf cap over C-72 ? This can really help with stability on freq ? I've been able to set them with out the cap at times , but most of the time the cap is a plus for locking freqs' in .
thankyou SwitchKit that was the key to solve the problem. this is what i did i just followed the service manual CH:40,AM,RX Clarifier in center. Test point 2 adjust L13 for 4.5 V. then i checked CH:40 for right reading frequency on all three postions then switch to channel 1 adjust L38 as you say and bingo i got the right reading frequency on all three postions thanks again.
Did you use the 27pf cap over C-72 ? This can really help with stability on freq ? I've been able to set them with out the cap at times , but most of the time the cap is a plus for locking freqs' in .
thankyou SwitchKit that was the key to solve the problem. this is what i did i just followed the service manual CH:40,AM,RX Clarifier in center. Test point 2 adjust L13 for 4.5 V. then i checked CH:40 for right reading frequency on all three postions then switch to channel 1 adjust L38 as you say and bingo i got the right reading frequency on all three postions thanks again.
Thats great Jose 
glad to read you got it going. IM going to start sending all my stuff to you . Good going.
glad to read you got it going. IM going to start sending all my stuff to you . Good going.
i just finished the project i was working on cobra 146gtl
heres the pictures and video
YouTube - radio
Thanks for watching and for your support 73,s
heres the pictures and video
YouTube - radio
Thanks for watching and for your support 73,s
Hello is this a picture of your PC122XL with the Galaxy N kit installed , I am getting ready to put mine in the Novice 10 meter band. I found a place to but the N kit although I may just make my own. kb3kwy@verizon.netWell Bob , I really don't know about all that. But FM is basically not used here in the states (or at least not by me) I had asked AC the same questions I had asked you concerning this radio and the Galaxy N kit , well I figured it out , the directions were wrong unless the President AX-144 / Uniden AR-144 is slightly different from the Cobra 146 GTL ?
I've seen and been through variations of this board before , I believe the TRC-451 is also this chassis (Uniden made) the PC-122s and TRC-456s and TRC-453s are close but built somewhat differently. And the fact that they put mic gains on the AX and AR - 144s
I have never had much luck with Expo N Kits with there cyrstals , (they were always very hard for me to stabilize on freq) in the late 90s these Galaxy N Kits (blue box) came out with there two IC's , although they can be set for the lower freebands , higher freebands or even 10 meters ,with vco and down mixer adjustments, you can only have the choice of one. For me and SSB's radios , it's always the upper freebands from 27.425 to 28.045 I set them on.
The Galaxy N's are very stable channel kits with usuallly ease of installation. These kits will work in both AM and SSB type radios with many different pll styles.
Cannot get it locked in.........
Nothing like reviving and old thread.............
I've used this thread to put a couple of Galaxy N kits in radios with very good luck. I've run across one nut I cannot crack.
The radio is a Midland 7001....basically the same chassis as the 146GTL. I just cannot seem to get the VCO dialed in. It's wired properly and looks just like the last set of pics posted here.
In tuning L13 I cannot for the life of me get the spread I need to cover the regular band and then to get the PLL to lock when using the switch in high or low position. It takes a tiny tweak to get it to lock when I move the switch but it just will NOT do both when going from normal to high or low. When I do get it to lock when the switch is activated, it doesn't have the full 40 channel coverage without falling out again.
Any suggestions? I've done the swap according the the instructions....and I've stopped before I wear out the tuning cans ! ! !
Nothing like reviving and old thread.............
I've used this thread to put a couple of Galaxy N kits in radios with very good luck. I've run across one nut I cannot crack.
The radio is a Midland 7001....basically the same chassis as the 146GTL. I just cannot seem to get the VCO dialed in. It's wired properly and looks just like the last set of pics posted here.
In tuning L13 I cannot for the life of me get the spread I need to cover the regular band and then to get the PLL to lock when using the switch in high or low position. It takes a tiny tweak to get it to lock when I move the switch but it just will NOT do both when going from normal to high or low. When I do get it to lock when the switch is activated, it doesn't have the full 40 channel coverage without falling out again.
Any suggestions? I've done the swap according the the instructions....and I've stopped before I wear out the tuning cans ! ! !
Perhaps the VCO has a weak electrolytic cap or two.
After all; and old radio has old radio problems.
Given that everything else is equal, as you claim it to be . . .
EDIT:
C68 & 69 are tantalum 2.2uf caps; that is what I would check/replace for starters.
http://www.cbtricks.com/radios/cobra/146gtl/graphics/cobra_146gtl_sch.pdf
After all; and old radio has old radio problems.
Given that everything else is equal, as you claim it to be . . .
EDIT:
C68 & 69 are tantalum 2.2uf caps; that is what I would check/replace for starters.
http://www.cbtricks.com/radios/cobra/146gtl/graphics/cobra_146gtl_sch.pdf
Last edited:
Nothing like reviving and old thread.............
I've used this thread to put a couple of Galaxy N kits in radios with very good luck. I've run across one nut I cannot crack.
The radio is a Midland 7001....basically the same chassis as the 146GTL. I just cannot seem to get the VCO dialed in. It's wired properly and looks just like the last set of pics posted here.
In tuning L13 I cannot for the life of me get the spread I need to cover the regular band and then to get the PLL to lock when using the switch in high or low position. It takes a tiny tweak to get it to lock when I move the switch but it just will NOT do both when going from normal to high or low. When I do get it to lock when the switch is activated, it doesn't have the full 40 channel coverage without falling out again.
Any suggestions? I've done the swap according the the instructions....and I've stopped before I wear out the tuning cans ! ! !
Try a bigger capacitor at C75 from 27pf to 58pf in parallel and parallel an NTE614 Diode at D25
Tantalum capacitors don't dry like electrolitycs,they work or don't work
For the Midland 7001, it uses a different loop mixer scheme than the standard Cobra 146GTL. While it uses a similar PLL chip (D2816) you HAVE to make sure that pin 20 of the PLL chip is floating (ie not grounded, or tied "hi" to the PLL control voltage) in order for the Galaxy "N" kit to work. The D2824 PLL used in the Cobra 146's do not have a T/R shift function in the PLL, which is on pin 20. However, on the Midland 7001, since they use the D2816 PLL, that PLL DOES have the T/R shift function (455khz), and it is controlled on pin 20. Since the T/R shift pin is grounded in this case, tying this pin "hi" (to the PLL control voltage, +5V) will cause it to shift 455khz BELOW normal CB frequencies, or 26.510-26.950. You do not want this pin in any state other than floating, since the Galaxy "N" kit is a reference divider, and changing the state of pin 20 will not allow the Galaxy "N" kit to divide the reference frequency properly before it goes to the tripler can (L13).
You have to isolate pin 20 from ground before you can make any modifications. Try isolating pin 20 from ground, and see if you can dial in the extra frequencies. Let us know how you get on. Good luck!
~Cheers~
You have to isolate pin 20 from ground before you can make any modifications. Try isolating pin 20 from ground, and see if you can dial in the extra frequencies. Let us know how you get on. Good luck!
~Cheers~
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I forgot to add that the 7001 I have is a Domestic 40 channel version....not an export.....so my 7001 has a D2824 PLL. The entire board in this radio looks almost identical to the 146GTL.....up to and including the component numbering scheme. It literally is a twin of the 146GTL.
The Galaxy N Kit comes with a 100 pf NPO type cap which replaces C75 in the circuit. I can certainly try the diode...
Appreciate the suggestions guys.....keep em' rolling ! !
The Galaxy N Kit comes with a 100 pf NPO type cap which replaces C75 in the circuit. I can certainly try the diode...
Appreciate the suggestions guys.....keep em' rolling ! !
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The export version uses a Cybernet chassis and uses a different PLL.
The domestic version is suppose to have a D2816 PLL in it. Might want to double check to see if someone swapped out the PLL on that radio, as my schematics show a D2816, and the couple I have modded in the past have have had D2816 PLL's also. Interesting that yours has the D2824. See if someone soldered in a different PLL, let us know how you get on.
~Cheers~
The domestic version is suppose to have a D2816 PLL in it. Might want to double check to see if someone swapped out the PLL on that radio, as my schematics show a D2816, and the couple I have modded in the past have have had D2816 PLL's also. Interesting that yours has the D2824. See if someone soldered in a different PLL, let us know how you get on.
~Cheers~
The PLL in the radio appears to be a factory original. The soldering job is way too clean to have been re-done.
Going to try a couple things when I get back home this next week. (traveling this weekend)
I'll let you know how it goes and perhaps put up a few pics.
Going to try a couple things when I get back home this next week. (traveling this weekend)
I'll let you know how it goes and perhaps put up a few pics.
I made some incremental progress last evening. I shortened up the "yellow" wire, (feeds the downmixer coil), a considerable amount by drilling through the PCB, (in an open area to affect nothing else), and re-soldering the wire back to the board. This cut about 3.5" off the length of the wire. I can now get all 40 channels to lock in the middle "Normal" position of the expander board and the "Low" position of the switch on the expander board. When I go to the "High" position of the switch on the expander board, I can get channels 1-20 to lock, but any higher and it falls out of lock. I can get a few channels higher adjusting the VCO coil, but then I start to loose what I accomplished on the other two switch positions.
So.....any ideas how I can get this last little piece of goodness ??? So far I have done the following:
-Removed C75 and replaced with tantalum cap provided with kit.
-Removed and transplanted C72 according to kit instructions.
-Shortened up the Yellow downmixer feedline as much as possible.
I need to get this thing to lock on the last 20 channels in the high range....and cannot seem to get it there !
Thanks
So.....any ideas how I can get this last little piece of goodness ??? So far I have done the following:
-Removed C75 and replaced with tantalum cap provided with kit.
-Removed and transplanted C72 according to kit instructions.
-Shortened up the Yellow downmixer feedline as much as possible.
I need to get this thing to lock on the last 20 channels in the high range....and cannot seem to get it there !
Thanks