Cobra 142 GTL Weak Mod Ok AM Power.
SSB is weak also.
Tried re-align as per SAM's with two tone signal generator...no real gain.
Replaced Finals...no change...replace IC4 AF Output TA 7222P...no change.
IC4 voltage's not correct!
PIN 2 = High @ 7+ volt should be 2.95v
PIN 5 = Low @ 1.1v should be 1.9v
PIN 6 = Low @ 1.17v should be 1.9 volt
Any Ideas?????
Cobra 142 GTL Weak Mod Ok AM Power
Re: Cobra 142 GTL Weak Mod Ok AM Power
Have you tried replacing the mic? SSB and AM being weak would suggest that the fault is mic related as the radio does not use the TA7222AP in SSB mode and is only used in the AM mode. Have you tried a PA test as this may help narrow the fault down? Question what is the output power on AM and SSB. Hope this helps. Lets us know how you get on.
Rick.
Rick.
Cobra 142 GTL Weak Mod Ok AM Power
I have tried various Mics Including: Astatic D104 Silver Eagle & D104-M6B
as well as Stock Cobra and President Mic's.
I did not know that the TA 7222P was not used for SSB mode, so that info will help narrow it down (SSB is weak too)...I am still concerned about the low voltage on Pins 5 & 6 as well as High voltage on Pin 2 of the TA 7222P.
I will try the PA speaker audio and post the results.
I have a President Mckinley mobile for comparison that is now working good. I had blown the voltage regulator during a coil retune. I replaced many parts in vain starting with the Finals the MB3756 solved the problem. It is now dead keying 4 1/2 watts swing to 15 AM with 100% mod on AM
SSB swings 15 watts and will swing 100% mod.
This Mckinley uses the same basic PC board as the Cobra 142 GTL and is more like like Cobra 140 GTL mobile.
Using BluePoint DVOM
and Palomar PW-5000 for testing.
as well as Stock Cobra and President Mic's.
I did not know that the TA 7222P was not used for SSB mode, so that info will help narrow it down (SSB is weak too)...I am still concerned about the low voltage on Pins 5 & 6 as well as High voltage on Pin 2 of the TA 7222P.
I will try the PA speaker audio and post the results.
I have a President Mckinley mobile for comparison that is now working good. I had blown the voltage regulator during a coil retune. I replaced many parts in vain starting with the Finals the MB3756 solved the problem. It is now dead keying 4 1/2 watts swing to 15 AM with 100% mod on AM
SSB swings 15 watts and will swing 100% mod.
This Mckinley uses the same basic PC board as the Cobra 142 GTL and is more like like Cobra 140 GTL mobile.
Using BluePoint DVOM
and Palomar PW-5000 for testing.
Re: Cobra 142 GTL Weak Mod Ok AM Power
It maybe worth check the Dyna Mike control VR405, C83, C84, C121 and transistors T27, 28, 29, 30, 31, 32 and 33. The voltages around the audio chip maybe just a red herring. Due to the age of the radio is most like that the electrolytic caps have dry out which maybe causing the problem.
If you have a scope you could find the fault very quickly.
Rick.
If you have a scope you could find the fault very quickly.
Rick.
Cobra 142 GTL Weak Mod Ok AM Power-Working??
I was going to check the PA speaker audio but the radio has the Mod limiter switched On/Off threw the PA/CB switch. While looking into a remap of the PA switch and to put the Mod limiter back to original I found a bad solder joint at the PLL. Although it did not appear to be the real problem either?? Cleaned up some solder splatter with a small screwdriver and a toothbrush.
I was going to recheck the output as you had requested and for whatever reason it seems to have good swing on the watt meter (4 1/2 dk @ swing 14-15 watts w/mod ) and full 100% Mod even using a stock Mic. With the D104 I had to drop the Mic gain on the radio to half throttle and still 100% on meter!
SSB has swing at 14-15 watts and 100% Mod.
I then rechecked the voltages on the TA 7222P, but they have not changed.
Still high on Pin 2 and low on Pin 5 and Pin 6.
I bought this radio used about 17 years ago and I dont know if the Mod was good before the channel mod was done. It just didn't have the mod that other Cobra / Uniden radios have. Years later out of desperation I had some of the lower channels taken out thinking it was just to widebanded. It used to go down to 26.165 up to 28.085 now it is 26.815 to 28.085
I hope this is for real! I sure like to see that mod meter kick up there!
Thanxs to all for your help. For some reason I had no responses on the Copper Forum posts while I was working on the Mckinley???
I was going to recheck the output as you had requested and for whatever reason it seems to have good swing on the watt meter (4 1/2 dk @ swing 14-15 watts w/mod ) and full 100% Mod even using a stock Mic. With the D104 I had to drop the Mic gain on the radio to half throttle and still 100% on meter!
SSB has swing at 14-15 watts and 100% Mod.
I then rechecked the voltages on the TA 7222P, but they have not changed.
Still high on Pin 2 and low on Pin 5 and Pin 6.
I bought this radio used about 17 years ago and I dont know if the Mod was good before the channel mod was done. It just didn't have the mod that other Cobra / Uniden radios have. Years later out of desperation I had some of the lower channels taken out thinking it was just to widebanded. It used to go down to 26.165 up to 28.085 now it is 26.815 to 28.085
I hope this is for real! I sure like to see that mod meter kick up there!
Thanxs to all for your help. For some reason I had no responses on the Copper Forum posts while I was working on the Mckinley???
Cobra 142 GTL Weak Mod Ok AM Power-Working??
For some reason the RF driver bias is jacked up and I can barely bring it dowm to 60+ mA...but TX / RX seems to be woking good.