Hey, I am having frequencies issues with a Cobra 29 LX BT, I replaced the Crystals in the radio, the 10.695 was bad. Now I can get receive, but it is off frequency, can I get a process of how to go about setting the 10.240 and the 10.695 transmit and receive Crystal frequencies on the radio. I am getting transmitt,very scratchy as it is off and very low receive. I appreciate any help from anybody, all I need is the tuning process of the crystals. Thank you, enjoy the day, Mark, KB9GTB. All it needs is the Crystals retuned and set at the transmit and receive frequencies.
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Setting frequencies on a Cobra 29 LX BT, after Crystals replaced.
- Thread starter Mark A Bradley
- Start date
I don't think that radio has a 10.695 MHz crystal, does it? The PLL has a built in 455 KHz upshift offset when in TX, and the 10.240 MHz oscillator is mixed into the TX mixer.
Yes, It has 2,10.240 and 10.695,this is the LCD screen 29,with the Bluetooth,and you can change the colors of the front panel.It just seems that I cannot get the frequency to stay. I peak out the first 2 cans, set the 3.50 Volts,then align the receive, and then go to the transmit. I do use a signal generator and set it to what the manual tells me,I have the radio tweaked to the max, I see the frequency is just about on the transmit 27.1185,as I am on 19, and then it seems when I go to do the 10.695 and the transmit frequency, the 10.240 goes out of wack. I keep retuning the coils and then before you know it, everything is all out of frequency. Either I am doing something wrong, or the radio mat also have a bad 10,240 Crystal,I do not know, until I get the exact procedure to set the Crystals. This is where I stand right now, confusing to explain, hope you understand what I am going through and doing. Thank you...
http://www.cbtricks.com/radios/cobra/29_lx_le/index.htm
Looks like this one, except with Bluetooth built in?
Looks like this one, except with Bluetooth built in?
I believe the name is Glen, thank you for the link, I have been through that alignment, what I need is,the way to set the frequency's on the Crystals. I know if you to the alignment that the frequencies get really close to the settings, I was wondering if there is a different way to do this if they are still off center. What I will do is do the alignment again, and see again, if the frequency gets close to the settings for the Rx and Tx, but it seems that to set one the other goes off frequency, does not make sense to me. I am also going to throw in a 10.240 Crystal, I did the 10.695, as I cannot believe that 2 Crystals would go bad in one time. I will update this evening, after I am doing doing it again. Talk soon,wish me luck that it is another Crystal, nothing left to adjust.
The 10.695 crystal you refer to, did it have 3 legs and was between 2 metal IF receive transformer "cans"? This is not a crystal, er actually, it is a crystal of a sorts, but it is not an oscillator crystal, it is a Monolithic Crystal Filter.
This is used to narrow your receive frequency window so you minimize as much of the adjacent channel bleedover as it can.
You would need to repeak the "cans" before it and after in Receive.
Do you have a frequency counter and an oscilloscope?
And, most people know me as Rob, from my middle name Robert.
This is used to narrow your receive frequency window so you minimize as much of the adjacent channel bleedover as it can.
You would need to repeak the "cans" before it and after in Receive.
Do you have a frequency counter and an oscilloscope?
And, most people know me as Rob, from my middle name Robert.
Yes, I have all the necessary equipment, I will have to look again, I am certain when I took that out, it had a 10.695, and I kept it separate from my other Crystals, but this has it's own markings on it. I added the pic of the Crystal. I am going to finish the yard and get on the radio, I will post my outcome this afternoon, and before I start, I am also going the throw a 10.240 Crystal in also, and see what goes on now. To be continued, THANK YOU for helping me out, all is definitely appreciated from all.
Attachments
One more thing, nice to meet you Rob, I just looked at your first name on the ARRL website. I appologize if I have it wrong, there were only 2 with that call, and one was not registered, so I figured this was you left,LOL..I took a stab at it and called you Glen, and I am sorry if I offended you in any way Rob..Talk soon, sorry, and thank you, Mark
Put that 3 legged crystal filter back in, it will help you with the RX alignment later. Unless you replaced it with another 10.695 crystal filter.
http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29ltd_sm.pdf
The alignment procedures start on page 13 of this.
The LX version merely adds the fancy computer controlled LCD display control panel in the front to control the same (mostly) main radio board design they had been using since the days of the 29GTL. They have changed manufacturers several times, changed the PLL from a uPD2916 to a "Cobra29" chip, which they are having made to replace the uPD chip, and they changed the main audio chip from a TA7222 to a TDA2003 (TA7222 was discontinued).
But, the main layout is still the same though.
Here are the schematics of the 29LX-LE, if yours has BT added, that is an add-on board to the mic input to the front, like the 29LTD-BT model.
http://www.cbtricks.com/radios/cobra/29ltd_bt/index.htm
As to my given name, I didn't know my first name was Glen (with 1 N ;-) until I first went to Kindergarden, when they asked me which do I prefer to be called. So, mainly for legal purposes or the bank, I am Glen. But most everybody else knows me as Rob, some know me as either or both.
NZ8N in Tampa.
http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29ltd_sm.pdf
The alignment procedures start on page 13 of this.
The LX version merely adds the fancy computer controlled LCD display control panel in the front to control the same (mostly) main radio board design they had been using since the days of the 29GTL. They have changed manufacturers several times, changed the PLL from a uPD2916 to a "Cobra29" chip, which they are having made to replace the uPD chip, and they changed the main audio chip from a TA7222 to a TDA2003 (TA7222 was discontinued).
But, the main layout is still the same though.
Here are the schematics of the 29LX-LE, if yours has BT added, that is an add-on board to the mic input to the front, like the 29LTD-BT model.
http://www.cbtricks.com/radios/cobra/29ltd_bt/index.htm
As to my given name, I didn't know my first name was Glen (with 1 N ;-) until I first went to Kindergarden, when they asked me which do I prefer to be called. So, mainly for legal purposes or the bank, I am Glen. But most everybody else knows me as Rob, some know me as either or both.
NZ8N in Tampa.
Hello Tampa,,it was the 10.240 Crystal or a bad solder. I replaced this Crystal, and reinstall the other Filter or Crystal, it has the 10.695 writing on it, either one it us back in the board. Now the 10.240 and the 27.1185 stays one, may drift a few re adjusting the receive, but not as bad as it did before. I also went over the solder on the Pots, I went over the audio area solders and mostly the important areas of the board. I may have had 2 bad solder joints also, when I saw these solders, I hooked up the signal tracer, and one of the solder areas showed no contact, or a faulty part, went over the solder with the heat and the signal tracer started picking it up, bad solder there.
The radio seems to be working now, staying on the frequency it is to be at, either the Crystal was bad, a few of the pots needed to be reheated and re-soldered ,but it seems to OK now.
That was a tricky issue, it is hard to believe a Crystal may go bad, but I guess it happens.
What do you think of the IRF520 Power Mod, have you heard of any issues with this Mod, or do I do the right thing and leave well enough alone, I would like a bit more punch out of the radio, but all I have to do is lower the power a hair, and just use my Amp, it will do around 350 or more, more in, more out. But I have a main trucker route 1/2 mile away, and do not want to piss off these Truckers, I am in Cedar Lake,Indiana, and off the main Indianapolis Blvd, Route 41, main cut through, I think this is a side route for the trucks to get to Chicago, and the Southern Suburbs. I think my Base, with 350 Watts+ may screw up there radios, so I may leave well enough alone with the Amp, and just enjoy my 10 Watts I set it at and just talk to my Buddies, and leave the Mods alone.
One question, do you trust these Power Mods, do they work, smoke the radio, what is you opinion Sir? Mark
The radio seems to be working now, staying on the frequency it is to be at, either the Crystal was bad, a few of the pots needed to be reheated and re-soldered ,but it seems to OK now.
That was a tricky issue, it is hard to believe a Crystal may go bad, but I guess it happens.
What do you think of the IRF520 Power Mod, have you heard of any issues with this Mod, or do I do the right thing and leave well enough alone, I would like a bit more punch out of the radio, but all I have to do is lower the power a hair, and just use my Amp, it will do around 350 or more, more in, more out. But I have a main trucker route 1/2 mile away, and do not want to piss off these Truckers, I am in Cedar Lake,Indiana, and off the main Indianapolis Blvd, Route 41, main cut through, I think this is a side route for the trucks to get to Chicago, and the Southern Suburbs. I think my Base, with 350 Watts+ may screw up there radios, so I may leave well enough alone with the Amp, and just enjoy my 10 Watts I set it at and just talk to my Buddies, and leave the Mods alone.
One question, do you trust these Power Mods, do they work, smoke the radio, what is you opinion Sir? Mark
Sorry for the late reply, the 10.240 Crystal was bad
, I could not get down to that freq, installed the new one, and bingo, had it in no time. Then I got the POP, and everything just started to work, had the tune the transmit6 a bit, and receive was pretty darn close. Thank you for the tips, worked out great.
I am thinking of putting in IRF730's, Mosfet, can I use both for the driver and final, I never messed with these and feel like trying these out, as they are Chinas transistor's, and who knows if they will work,,maybe 1 out of 20....I jusy feel like trying something old, but new,and questions for me, feel free to ask,,Have a great Monday off,
, I could not get down to that freq, installed the new one, and bingo, had it in no time. Then I got the POP, and everything just started to work, had the tune the transmit6 a bit, and receive was pretty darn close. Thank you for the tips, worked out great.
I am thinking of putting in IRF730's, Mosfet, can I use both for the driver and final, I never messed with these and feel like trying these out, as they are Chinas transistor's, and who knows if they will work,,maybe 1 out of 20....I jusy feel like trying something old, but new,and questions for me, feel free to ask,,Have a great Monday off,
B
baconater4749
Guest
Diesel stinks,raw or burnt,gag me with a spoon. And I own a diesel,cannot stand the smell of diesel,and I drive F250 Superduty,7.3 litre,truck. Does not make sense.
B
baconater4749
Guest
I am just getting in to messing with CB's,as I work on trucks and cars for 30 years,back cannot go any more,so I pick up this hobby,messing with these CB's. Been a ham operator since the early 90's,this is when I had to do ,10 words a minute in CW,I believe I did around 13 words a month nite,and of course,I forgot most of the letter beeps,it has been a while. I figured doing this radio,repairs and mods is a bit easier to hat breaking my back working on vehicles,and the wife won't let me work on any vehicles,even my Father's van and car.So,I started this when the Government grounded us last year,still learning these CB radio's,and lots of reading to do. Oh well,my back feels better working on these radios,lots to learn about the way they work,but I have the concept of repairing them,at least the Cobra brand radio. No I am looks Ng at a HR2510,that is a interesting setup,but I believe I can handle this one,first sideband I gave ever worked on.Wish me luck,LOL.
