cobra 148 gtl locked up on tx all the time

[doc holliday]

i have a cobra 148 gtl with the mb8719 pll chip in it. it is locked on transmit both am an ssb. any suggestion?

[smokinjoe]

Check to see that someone has not replaced TR38 and installed it wrong i have seen this happen and cause this problem. If the driver has not been replaced and is installed correctly check the keying transistor it may be shorted not sure what the TR number is right off maybe Rick or someone will chime in and give the correct number hope this helps.

[doc holliday]

I checked tr38 it is ok i am prety sure its the keying transistor.. but don't know the tr number.

[smokinjoe]

TR38 is the 2sc2166 driver the keying transistor is located toward the front of the radio hopefully some one will get the number for you if not i will try and look it up for you tonight.

[doc holliday]

ok thanks . when ever you get a chance.

[smokinjoe]

Try checking TR21 voltage in RX b. 0.24v c. 2.99v e. 0v and in TX mode b. 2.55v c. 1.87v e. 0v. If the volts are ok check TR22 and TR23.

[doc holliday]

I checked tr21 22 23 with a transistor checker they are ok.. radio is still keyed up all the time

[smokinjoe]

Is the fault still there even when the mic is not connected to the radio?

[doc holliday]

yes it is doesn't matter if the mike is pluged in or not

[Rick]

As you have given very little information has to which model of Cobra 148GTL, I will assume that this the model with the voltage regulator IC4 bolted to the side of the chassis if this is so.
First try removing TR35, if it stops transmitting then replace TR35 with a new transistor, if it is still stuck in the TX mode unsolder Pin 8 of IC4, if it stops transmitting then replace IC4 (MB3756).

[doc holliday]

Rick I tryed what yo said an it stayed keyed up untill i unsoldered pin 8 of ic 4... so I am replacing it when i find the part...hopely soon..well let you know what it does....thanks alot.

[doc holliday]

I replaced ic 4 ..... radio works fine now.... thank you Rick