Cobra 148 GTL
PC-412
No mods yet Clarifier was unlocked but back to stock now
I cant get the frequency to align, keeps jumping around, If RX is close enough to have ears, TX is way low.....
I have 12 volts on pin 9 of IC 1 Pulled the chip and I still have 12 v on the PCB A working 148 I have beside it on the bench is 9 v any clue where to look?... I'm gettin frazzled on this one....
Last edited by RedEye on Saturday 6th Jan 2007, 17:41, edited 1 time in total.
Thanks a Ton Rick!!! It was bad, I replaced it and now it's stable... but the new problem is now it wont change frequency, all channels are the same freq. Replaced the 8719 and still no change. L23 dosen't change freq when turned.... Arrrgh!!! I double check for solder bleed over all clean...
Have also replaced tr 20, tr 28
If you have changed the PLL with a good one? then it sounds like IC2 UHIC 007 which is the VCO they do not like 12 volts, you may also find the bal mod IC has also blown IC3 AN612. Hope this helps. let us know how you get on.
Replaced IC3 ( you were right again!!!)Freq stable now... but.... No change in freq when channels switched..
Freq adjust is now through L20 and L23 makes no change...
IC1 pin 8 freq is 2.8~3.0 not 10.240 - Changed crystal and both caps C85-C86 - No change... I can adjust L20 (?!? not L23) and get 27.1850 stable and can RX and TX but no change on the channel selector...
4 volts on IC1 Pin 8 and crystal - 3.2 volts on other pin of crystal...
Thanks again Rick for putting up with this crazy radio with me.....
It sounds like the PLL is put out a out of lock voltage, what is the voltage on Pin 6 of the PLL? and pins 11 to 16 do they change when you change channel? and what is the voltage on TP9 and TP10?.
The PLL is unlocked pin 6 should be about 7vdc if working correctly, this can because by various faults. You need to set you DC input voltage to 13.8 VDC with the wrong input voltage all checks you do will be wrong. Check transistors TR20, TR29 and TR30. Do you have a frequency counter?
Yes I do have a freq counter, I'll switch to my other PWR supply, the volage is variable so I'll set it to 13.8
I normally dont use it because it does not have a high amp output, only about 2 watts..(Analog/Digital test pad w/ +/- 12v +/- 5v)
I'll check the tr's and get back.....
Right now I can "tune" channels in by adjusting VERY slowly L19 & L20
TX matches the freq input i "tune" and tx just fine - RX is working well too, Just not from the channel selector... if on Chan 19 and adjust L20 to rx 27.185 then Chan 18 is about 27.1770 and Chan 17 is back to 27.1850
heh heh - go ahead...... tell me.... put it on the shelf and use for parts......
Check the frequency at TP10 using a 10 to 1 probe, also check the frequency at the emitter of TR20 and check the frequency at Pin 1, 7 and 8 of the PLL, change channel while monitoring the frequency's, let know how you get on.
RedEye,
It sounds like you have put the PLL chip in the wrong way round. Check that Pin18 is ground and pin1 is connect to junction of R95, R96 and R99.
