CB World Informer December 1996 Issue, Midland 79-290 Review.
Excerpt from that page:
The following will unlock and keep the standard clarifier range:
Remove D58
Follow the wire (white or green) from R44 and remove the other end from the PC board and connect it constant +8 volts (IC4 pin 3).
I like this method because it keeps VR5 active so that the TX frequency can be adjusted. Pulling D52 - as the other mod on this thread suggests - makes VR5 inactive. And if the radio is off TX freq - probably - you are in a world of hurt. You need VR5 if you want the radio to be dialed in with your frequency counter for alignment purposes.
I use the method - on that page/link I provided - that does't extend the slide range - and doesn't clip D52.
As it also makes it much easier to clarify since it will slide only ~2kc's either way.
First, lift just one leg of D58 off of the board; it is near the squelch VR near the front of the radio.
Next, there will be a wire near R44 - that also goes to a point near that squelch VR.
Lastly, unsolder that same wire - from the point near that squelch VR - and route it to C84 "+" side (IC4 pin 3).
OR to the "+" side of the 8v regulator - either way is fine.
That should check on your voltmeter as being +8v from the voltage regulator.
CHECK IT FIRST!
This source gets solid +8v in TX and RX; that is necessary.
Then, center the clarifier knob and then re-align the VCO.
Done.
(not responsible for work done wrong)
I've gotten a couple of used 148's and GrantXL's that had the 'D52 clipped'/method from locals or a hamfest that needed their radios aligned. I then reversed their work and did it by the method above. It aligns correctly when VR5 is working as it should.
I did unlock this reviewed Cobra 148GTL - BTW.
I also aligned it and put in four Shottky 1N6263 diodes (D1, D2, D21, D22) and two Sanyo 2sc2999e's (one for AM and the other for SSB - TR14 and TR19).
This radio could NOT have been aligned as I requested for this review. It was waaay off, even before unlocking the clarifier. The net result after a full alignment was favorable; it really got great reports. Got 4-12 PEP on AM and almost 17 watts PEP on SSB.
Here is another thing that can be done for the 148 - that I have not seen anywhere on the 'net . . .
The first step in aligning the Cobra 148/GrantXL is to check pin 8 on the PLL chip for 10.240000mhz +/- 20hz. Chances are, it will be off - even if it is new. What to do? Remove C85/10pf next to the 10.240mhz crystal, and install a 3-18pf variable capacitor. Either on top of the board or underneath the board - whichever is easiest and more convenient for you to do. Now you can adjust pin 8 of the PLL to exactly 10.240000mhz +/- 20hz! Also works on the 142 and probably other Cobra radios that use the 8719 PLL chip. Works great. Either you get a new 10.240mhz crystal for ~$6; or you can spend $.40 for an adjustable capacitor. Even new crystals aren't exact - BTW. So it is worth the time and effort for this simple and cheap mod. I've done it to all of my 148's and XL's . . .
Excerpt from that page:
The following will unlock and keep the standard clarifier range:
Remove D58
Follow the wire (white or green) from R44 and remove the other end from the PC board and connect it constant +8 volts (IC4 pin 3).
I like this method because it keeps VR5 active so that the TX frequency can be adjusted. Pulling D52 - as the other mod on this thread suggests - makes VR5 inactive. And if the radio is off TX freq - probably - you are in a world of hurt. You need VR5 if you want the radio to be dialed in with your frequency counter for alignment purposes.
I use the method - on that page/link I provided - that does't extend the slide range - and doesn't clip D52.
As it also makes it much easier to clarify since it will slide only ~2kc's either way.
First, lift just one leg of D58 off of the board; it is near the squelch VR near the front of the radio.
Next, there will be a wire near R44 - that also goes to a point near that squelch VR.
Lastly, unsolder that same wire - from the point near that squelch VR - and route it to C84 "+" side (IC4 pin 3).
OR to the "+" side of the 8v regulator - either way is fine.
That should check on your voltmeter as being +8v from the voltage regulator.
CHECK IT FIRST!
This source gets solid +8v in TX and RX; that is necessary.
Then, center the clarifier knob and then re-align the VCO.
Done.
(not responsible for work done wrong)
I've gotten a couple of used 148's and GrantXL's that had the 'D52 clipped'/method from locals or a hamfest that needed their radios aligned. I then reversed their work and did it by the method above. It aligns correctly when VR5 is working as it should.
I did unlock this reviewed Cobra 148GTL - BTW.
I also aligned it and put in four Shottky 1N6263 diodes (D1, D2, D21, D22) and two Sanyo 2sc2999e's (one for AM and the other for SSB - TR14 and TR19).
This radio could NOT have been aligned as I requested for this review. It was waaay off, even before unlocking the clarifier. The net result after a full alignment was favorable; it really got great reports. Got 4-12 PEP on AM and almost 17 watts PEP on SSB.
Here is another thing that can be done for the 148 - that I have not seen anywhere on the 'net . . .
The first step in aligning the Cobra 148/GrantXL is to check pin 8 on the PLL chip for 10.240000mhz +/- 20hz. Chances are, it will be off - even if it is new. What to do? Remove C85/10pf next to the 10.240mhz crystal, and install a 3-18pf variable capacitor. Either on top of the board or underneath the board - whichever is easiest and more convenient for you to do. Now you can adjust pin 8 of the PLL to exactly 10.240000mhz +/- 20hz! Also works on the 142 and probably other Cobra radios that use the 8719 PLL chip. Works great. Either you get a new 10.240mhz crystal for ~$6; or you can spend $.40 for an adjustable capacitor. Even new crystals aren't exact - BTW. So it is worth the time and effort for this simple and cheap mod. I've done it to all of my 148's and XL's . . .
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