The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

hello, i have a cobra 146gtl that will not tx or rx from channel 30 to 40 and from channel 1 to 29 is ok.i tried to adjust the VCO with no luck could it be the pll chip is bad?

You could just try replacing the PLL and what gives or if you have some test equipment DVM, Frequency counter you could test the PLL first. With a Frequency counter check TP4 the frequency should be for 16.270 to 16710 MHZ.

Rick.

well i dont have a 2816 pll to try but i did try a 2824 out of my cobra 29 but i t did not work so i put it back in my 29 with no problem?but one thing i forgot to mention is that i had a intermittent problem before i always had good rx but once in a while the tx would sound very bad i had to give a good wack on the radio to get it to work good again and could never find the problem always work good on the bench ?had the radio for about 3 years and it only happend mabe 1/2 a dozen time when i was mobile.

i was doing some reading on the net tonight and i was thinking it might be a VCO problem?how can i check?i have a few radio's for parts can i take the VCO in anyone of them to replace the one in the 146gtl if it is the problem?will it work??

Well with out any test equipment it is not very easy to find the fault, you can just keep changing parts until the fault is fixed but this is not the way to fix it. It maybe the VCO is not setup correctly, to set the VCO you need a DVM connect to TP2 and the radio on channel 1 adjust the VCO (L14) for 1.5 volts and on channel 40 you should have 4.5 volts. You may have a bad solder connection or dry joint; it may be a good idea go touch up all the soldering joints with new solder. I can not real give you any more help with you having the right test equipment.

Rick.

well i did check the voltage on the VCO about 2v on channel 1 and around 6.5v on channel 29 cant check channel 40 because it only transmit from 1 to 29, from 30 to 40 its 8.2 volt no matter the setting of the VCO?

If you can not adjust the VCO the likelihood is that the PLL is faulty

Rick.

thats what i was afraid of,the pll,anyway thanks for your info Rick and i will try to find a new pll to try and hope for the best .thanks

I may have a S/H PLL let me know if you wish me look for it, as it may take a day or so.

Rick (Euro Radio Co).