Galaxy 99v problems?

[smokinjoe]

I have a galaxy 99v 360014b main board that has a problem on channel 13 only the radio acts like it has a 7db carrier all the time on this channel but you can receive other signals over it. Every thing else on radio works fine. I noticed that when radio is on channel 12 i can turn clarrifier to with in 2khz of channel 13 and its not there but if i use the 10khz jump switch its still there. I also unhooked dummy load and carrier signal on the meter on channel 13 was still there but dropped 1 s unit. At first i thought it might be channel selector but i can switch to different bands with channel selector on 13 and carrier isnt there curious as to what may cause this could it be a bad ic? Thanks in advance to any replies.

[kc8mob]

Sounds like sombody has a CB on 13 around you.

You know, you hook one up to a car bat. and dead key the rig, you can kill somebodys recieve on what evber channel.

Good prank actually

[nomadradio]

Uh, that little problem is "built in" on the 8-band Galaxy radios. What you are hearing is the second-harmonic frequency of the so-called "offset" crystal in the radio's PLL section.

The PLL uses a crystal to "mix down" your VCO frequency in that radio. On CB channel 1, the VCO feeds 16.270 MHz (on AM mode) into the receiver mixer and the transmitter mixer. The 8-band Galaxy with that pc board uses a 13.56 MHz crystal to "mix down" that 16.27 so that what is fed into the MC145106 PLL chip's pin#2 is 2.7 MHz. Older 3-band radios from 15 years ago used 15.360 Mhz crystal. Later 5-band models used a 14.01 MHz crystal. When they expanded that radio's design to 8 bands, the crystal was dropped to 13.56 MHz.

Now, the older models all had this "second harmonic" frequency leaking into the receiver, but that would be 30.72 MHz, or 28.02 MHz on the older models. Nobody is listening to those frequencies, so nobody notices a problem.

With the 13.56 crystal, that second harmonic is now hovering between channels 13 and 14, more or less. Because that crystal is "pulled" up or down 2.5 kHz when you change modes, the frequency of your phantom carrier will move about a half of a channel if you look for it on USB or LSB.

Simplest cure is to rob a 14.1 MHz crystal from a junked early-90's 5-band or 6-band Galaxy/Connex/Superstar type radio. You'll have to adjust the three trimmer coils that set the clarifier to the center of the channel on each mode when that crystal is changed.

This doesn't make the second harmonic carrier go away, just moves it up to about 28.2 MHz where you probably won't be listening.

If the circuit around that crystal were laid out differently, you could consider shielding that circuit to keep that second harmonic from leaking into the receiver. But it's not a practical way to go about fixing the problem. Changing the 13.56 crystal to 14.1 will cause you to lose the lowest two bands. The highest two bands will now cover well into the 10-meter ham band, above 28.32 MHz where it stops now.

That carrier is built in. Besides, it's a 10-METER RADIO, RIGHT? Who's gonna listen to CB channel 13 or 14 with a 10-METER radio, anyway?

Or, that's probably what the engineers were saying to themselves when the marketing department told them to add two more bands to the six-band design.

73

[kc8mob]

Sometimes I get tired of typing.

[smokinjoe]

Thanks nomadradio you are right i never use channel 13 i was just curious as to what caused this problem. Thanks for the detailed explanation as to what was causing this and Thanks again to the forum and every one else who makes this site so helpful.

[Rick]

I had one like this last year to work on and it turn out to be the frequency counter I just unplug it and it stop, the cure was to add some de-coupling caps to the frequency counter and all was ok.

Rick.

[smokinjoe]

Thanks for the reply Rick i didn't try unplugging the frequency counter but i did turn it off and it didn't make any difference but i will try it to see if it works if it does what value caps did you use and where exactly did you place them? If it is to difficult to do with me not having much experience working on radios the 10 meter mod. may be the easiest way to go not sure which way will be best. Thanks for every ones help.

[Rick]

If you have tried unplugging it and it did not stop the problem then add de-coupling caps will not cure the problem. You could try re-aligning the PLL section and is if this helps you can find the info for this at www.cbtricks.com/radios/galaxy/dx99v/index.htm

I have worked on lots Galaxy over the years and it?s a fault which crops up from time to time.

Rick.

[smokinjoe]

Thanks for the information Rick i will unplug the counter this week end and see what happens if the problem is still present i will do the 10 meter mod. like nomadradio suggested and realign the pll section. I will let you know how things work out. Thanks.

[smokinjoe]

Rick tried aligning pll section and unplugged freq.counter and it didn't change anything so i did the 10 meter mod. as nomadradio suggested and that took care of it. Thanks for every ones help.