| Author |
Message |
    
Jose22
| | Posted on Saturday, May 11, 2002 - 9:24 pm: | 
|
Tech Man, just got a Cobra 142GTL and when vol.is up 2/3 or more get high pitched squeel. Has output of only 3/4 watt, Backward modulation, and bad receive. (could be someone has screwdrivered It). Where can I get alignment specs. and can you give help on vol. squeel. I figured Id fix the squeel first, receive second and tX output third. What do you suggest, and any leads on squeel.
73 |
Jose22
| | Posted on Sunday, May 12, 2002 - 2:55 pm: |
|
The squeal is in receive. transmit is clear except for very low output. it really does not have any receive, but can tell it is trying to receive when i key up another radio nearby. Tried another mike, same problem. even jumpered the pins on connection. Still squeal at 2/3 or more volume and almost no receive. Grounds appear good will check again. Didn't see talkback option, can you clarify? Thanks for directions. Will await your reply before i butcher this pig.
Thanks |
Jose22
| | Posted on Monday, May 13, 2002 - 9:51 pm: |
|
Tech 181, Went thru alignment procedures today. Cured receive and transmit problem. Out put at 6-7 watts modulates to around 15. Set back to 3 watts and modulate to 12-13 on AM. Modulation on scope showed way over 100 % with mike and dynamike up full,am able to regulate with both controls. The squeal is only when I turn volume up past 2/3. Checked all grounds, volume output at speaker seem fine except for squeal. When I use signal generator for s meter adj. it worked fine. CB nearby did peg meter but it is close.
I will check IC4 and nearby caps next day or so.
Thanks a lot . Will let you know. |
Cuddlebear
| | Posted on Tuesday, May 14, 2002 - 2:09 pm: |
|
Jose22,
Not for anything, But are you running a power mic or echo mic? The reason I ask this is because of the fact that I have a 142GTL Base. Great radio. But has one problem with it. When you run a power mic through it or my sadelta Echo master sometimes if you have the Dynamic also known as the mic gain open full bore on the radio and then you have the microphone setting itself turned up you get the feedback when the volume hits about half way. When I turn the mic gain on the radio down to about 4 it will stop the squeel. Try this. and let me know if it helps. |
Jose22
| | Posted on Tuesday, May 14, 2002 - 9:33 pm: |
|
Thanks Steve (Tech181) and Cuddlebear, I will look at both tomorrow and let you know. Thanks again for the suggestion and info. Would like to see the forum add a tech notes page by radio type which would allow neat tidbits of info like this. Thank again
73's
Jose22 |
Funtimebob
| | Posted on Wednesday, May 15, 2002 - 3:12 am: |
|
On the old Cobra 142 gtl if you removed the AMC transistor it would squeel like a pig on recieve. Interestingly enough on the RadioShack Trc-490 version if you removed the transistor you didnt have this problem...... |
Cuddlebear
| | Posted on Wednesday, May 15, 2002 - 4:00 pm: |
|
Good call Funtimebob,
Actually I had forgotten that little tidbit. But yes, it will do that as well. |
Bigbob
| | Posted on Thursday, May 16, 2002 - 8:43 am: |
|
Mike feedback squeal,put a 1000 ohm res. in series with mike line and a .01 or .001 mfd cap. in parallel will cure it,had same prob. in P-400 same board less some components. |
Jose22
| | Posted on Thursday, May 16, 2002 - 11:00 pm: |
|
AND THE ANSWER IS ...... Ok guys. I want to thank all of you for you input. It was helpful..I did check IC4..It showed ok on scope. All transistors in place. BUT... when I started tracing the squeal backwards, I was led to mike????? It worked ok..Pulled plug off and someone had wired the mike incorrectly. They had combined the common and ground together on the same pin.(5 wire) The tx and rx was correct. and audio ok,but the common and ground shared the same. This created the feedback. Split the wires and placed on the correct pins and, got the sausage grinder going. Squeal in pig gone. Was strange that the thing worked good this way untill vol. up past 2/3. Will keep all your suggestion for future ref. What do you guys think about a forum section to post repair tidbits by radio?
Thanks again
Jose22 |
Cuddlebear
| | Posted on Friday, May 17, 2002 - 5:17 am: |
|
DOH!!!
I knew that.... |
Jose22
| | Posted on Saturday, May 18, 2002 - 1:26 am: |
|
Tech181 both mikes from same source. thanks for help. |
|
