Cobra 2000 pll

[Ecvspokes]

Pll voltages are mostly wrong, And the freq at pin 8 is over 30 mhz could this mean that the Pll is bad? ecvspokes

 

[caspear1978]

The first question i have for you is what was the radio doing to make you look at the pll?

 

[Ecvspokes]

The radio was given to me from a friend as parts. It was pretty rough. No Receive or transmit no sound at all. When i looked i could see c92 by the pll and ic2 looked bad. I changed that and now all i get is static, but its a start. Louder on upper and lower ssb than on am.

 

[caspear1978]

it will always be louder static wise on upper and lower so yes you are right that is a good start,,,the reason why i asked what the radio was doing was ive seen pll chips go bad from some ppl trying to do a channel mods on it,, look at the bottom of the pll and see if you can tell if there was any soldering done to the pll or not that would be a good sign if some one tryed to do a channel mod or not,,,mark

 

[Ecvspokes]

Yeah they did, pin 10 on the pll. They hacked the anl, nb, cb]pa switches too, as well as cutting d23 in the middle of the board. TP 9 has no voltage at all. Spokes

 

[Carl]

did they change the pll to a 8719 or does it still have the mb8734 pll in it? the original mb8734 isn't modifiable for channels so it has to be changed.

 

[Ecvspokes]

yeah they changed it to a 8719. Spokes

 

[Robb]

You checked the VCO voltage @ Test Point 9 - and it showed nothing?
???
It should be 3.0v on ch 40 and ~2.0v on ch 1.
If no voltage there; then start at the voltage regulator/MB3756 for proper output.
Then trace from there to the PLL feed voltage.
BTW - there is a large electrolytic cap near the PLL chip (think it is C84?) that might be bad - a known fault. See if the PLL is getting ~8.0v feed @ pin 9 (I think that was it).

Be interested is seeing what you find was at fault. Be sure to update us on your next steps. I'll be watching this thread closely . . .

 

[Ecvspokes]

Yes its getting the 8v at pin 9. The voltages on the Pll are as follows, pin1=4.20, 2=3.06, 3=3.72, 4=3.5, 5=3.5, 6=8.14,7=2.10,8=3.5,9=8.23,10=7.78,11=7.78,12=0,13=0, 14=.28 15=7.73, 16=7.74, 17=3.5, and 18=0. Its alot I know! Spokes