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

hi all,i will try to describe what the fault is.
switch the radio on receives fine on all uk 40 channels,but will not transmit,now if i switch to pa and back it transmits and receives fine on the channel your on ,but then will not change channell.
now if i switch the channell 19 swich on and of the channels start working on the channel switch, but then the no tx comes back.

thanx in advance for any help

Check the VCO, and the RX/TX switching.

hi rick,can you give me a bit more info im a learner with cbs,what no is the vco in this radio and what volts ??.

and any chance if you have the alighnment info for the cobra uk 40 rick,

I do not have any alignment information for this radio, this is where experience comes in handy.

Check, the Emitter of Q206 in TX it should be about 8 volts.
Check, the Collector of Q207 in RX it should be about 8 volts.
Check, the frequency at C301 in TX.
Check, the frequency at D100 in RX.
Is this radio fitted with LC72322 MCU/CPU?
Let us know what results you find.

yes rick radio is fitted with LC72322N MCU/CPU,
which is the vco test component,?

just noticed when it transmits after switching pa on and off it is not receiving
but it does transmit .so to get it to tx i have to switch pa on and off and to get it to rx i have to switch ch19 on and off.

readings done on channell 1 uk 27601
c301 frequency in tx after switching pa on and off=26.036
e of q206 in tx=6.20 volts fluctuating

d100 frequency in rx after flicking ch19 switch on and off=16.870
c of q207 in rx=7.62 bolts

thanx rick

It looks like you have the all too common fault with this radio.
In that, the MCU/CPU has failed.
That is why I ask you which MCU/CPU was fitted to the radio.
The MCU/CPU was change in later radios just before they stop making the radio for a more reliable device.

You could check transistors Q403, 404, and 405 they could have a short no one or more of them, but it is most like to be the MCU/CPU.

ok rick i will check those.
also rick i have the cobra uk 29 ltd st that works fine so yesterday i did the channel unlock mod but its only working on some bands it wont lock/key on some seems like the vco needs adjusting,what do you recomend,which is the vco ther is 2 cans coverd in wax is it the 1 nearest the front.
thanx angus

The VCO is L501, DO NOT adjust L502.

hi rick,i have give up on the cobra uk 25 think yourright the mcu is cream crackerd.

but on the cobra uk 29 with the channell mod,i removed the top cover no speaker and it has had somekind of mod.do u no what it is ,there is a 5488 tranny a 103 cap 2 resistors 1 diod 1 piece of wire with 1 more resister on the other end it connects to c306 and into the area with the vco in with all the wax around and to the like small piece of circuit board with coils on stood up near c306.

also this radio was only putting out 3 watts.
and if you transmitted with the soundtracker on it just sent loads of feedback noise.
so i have now removed this mod ,and its now keying on all channels ,the wats has gone upto 10watts,and the feedback has gone seems like the radio is fine now what do you think will it be ok.
and also noticed it has a c1969 fitted.

thanx rick

rick where u gone ??????????