Loose crystal in 148gtl

[American-Vulture]

Got a 148 GTL from late 80's .Rattle inside.opened it up and a crystal was bouncing around inside.
Right next to L9 ,Can not read what it is. Any one know?It was rusted off the board.
Looked like water or coke got to it.Grey plastic coating on it.Probably should know what the value of the one next to L10 is also.That one is probably just as good.

 

[999]

X1 7.345
X3 11.325

http://www.cbradio.nl/cobra/Service_Manual_Cobra_148GTL_ENG.pdf

 

[loosecannon]

american vulture.

it's not coke.
it's called sony bond and its an adhesive they used back then (still do) to keep components from vibrating around.

the problem with it is that when it dries out it becomes corrosive to metal and conductive.

so the crystal you are talking about always has some of this goop on it and it sounds like yours corroded away.

there is probably a lot more of that sony bond all over the radio doing the same thing, and it needs to be removed before it takes out any more components.

you can use this stuff to re-soften and remove it:
https://www.newark.com/gc-electronics/10-312/chemicals/dp/92B1417

it is available from other places also.
LC

 

[American-Vulture]

X1 7.345
X3 11.325

http://www.cbradio.nl/cobra/Service_Manual_Cobra_148GTL_ENG.pdf

Know a place I can purchase these from?Or do I have to find some in other radio's?

 

[kopcicle]

http://www.kenselectronics.com/lists/cbxtal.htm

 

[American-Vulture]

Like around 30 bucks. don't even know if radio will work after replacing them.
maybe I can find some pulls in other radios.or even transfer them out of another radio.
to see if it works before I spend my hard earned money.

 

[loosecannon]

remember that one of those crystal looking things is actually a crystal filter and not an actual oscillating crystal.
the one with two legs on it is the 7.345mhz oscillator crystal.

the one with three legs on it is a 7.8mhz crystal filter.

not that it's going to be any easier to find than the crystal but at least you'll know what you're looking for.
LC

 

[American-Vulture]

I transplanted one out of another radio and it worked.Only one problem.
Channel 1 doesn't work all other 39 do .No tx or rx?light doesn't even change.

 

[loosecannon]

that's a VCO adjustment issue.

set the radio to channel 40, and connect a DC voltmeter to TP9 (bare lead of R207/pin 5 of the VCO chip)
with the negative lead going to PC board ground (not the radio chassis).

now set L19 for 3.5 volts DC.

go back to channel 1 and check that it is more than 2 volts DC.

you should have all 40 channels now.

in all reality, all you really need to do is give the VCO coil (L19) a small tweak in one direction, as your VCO is skewed to cover the higher portions but not all of the lower portions.

one easy way to do it is to set the radio for channel 1, key the mic, and slowly adjust L19 until the TX light turns red.
just don't turn more than about 1/4 turn in either direction.

hope this helps.
LC

 

[American-Vulture]

Thanks will give it a try.

 

[NZ8N]

If you remove R95 (1.5k), this will give you a little more "leg room" in the voltages that the PLL can send to the VCO on the lower end of the voltage scale.
Or increase to a higher value, like 4.7k or 10k.
This resistor pre-sets the voltage, or pulls it up, so the VCO will never see anything below about 1.5-2v, as I recall, I haven't worked on a 148 (or Grant etc...) in 20 years.