Copper Talk » Ask The Tech » Radio's Mobile » Archived Messages » Cobra 29LTD No TX audio « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Sunday, February 02, 2003 - 11:24 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

I have a 29LTD and everything works except the TX audio.

Any ideas?
Top of pagePrevious messageNext messageBottom of page Link to this message

307
Posted on Monday, February 03, 2003 - 4:11 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Have you tried another mic?

307
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Monday, February 03, 2003 - 4:38 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

The mic works fine. I've also tried other mics. I originally thought it was the audio IC, but RX audio is fine. I'm not sure what else to check. I've checked TR19, TR18, and a few others, and they seem to be good.
Top of pagePrevious messageNext messageBottom of page Link to this message

307
Posted on Monday, February 03, 2003 - 9:07 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Is the Audio getting through the Mic Gain Control?..To find out , disconnect the center lead on the Driver so no RF gets in the way and you can look at low level input audio signals on a scope from the mic plug all the way down the chain...
Top of pagePrevious messageNext messageBottom of page Link to this message

Ss8541
Posted on Tuesday, February 04, 2003 - 12:11 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

an easier way is to just gnd pin 4 of the mic jack. if you have a very loud talkback when mic is keyed and you talk into mic, then the audio is working all the way up to the output of the audio ic. if not, then it is time to start tracing from the input of the audio ic back toward to the mic.
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Wednesday, February 05, 2003 - 2:51 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

i tried the mic jack thing, since i don't have a scope, and the audio is not making it up to the audio IC. Any more suggestions on what to do?
Top of pagePrevious messageNext messageBottom of page Link to this message

Ss8541
Posted on Wednesday, February 05, 2003 - 7:45 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

to be honest, from here there are just too many other possibilities to give you a way to check without having a scope or audio detector. there are both passive and active components that could be shorted/bad.
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Wednesday, February 05, 2003 - 9:13 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

pin 4 of the audio IC is the input right?
Is there any way i can get something, or rig up something to detect audio?
Top of pagePrevious messageNext messageBottom of page Link to this message

Ss8541
Posted on Wednesday, February 05, 2003 - 10:12 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

no, pin 4 is the rx 'switch'. it gnds the 'return' lead of the spkr during rx so the audio from the ic can be 'heard' through the spkr. gnding pin 4 during tx keeps the return of the spkr grnded so you can hear the modulated audio.

there is an amplified spkr that you can get from radio shack that will work to detect audio all the way down to maybe even the mic level. let me see if i can find the part #. you will also need a cap to use this.
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Thursday, February 06, 2003 - 2:05 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

What would be a good oscilliscope to buy? I'm not looking to spend a fortune. Are there any "cheap" ones that are a decent deal?
Top of pagePrevious messageNext messageBottom of page Link to this message

Pinger
Posted on Tuesday, February 11, 2003 - 1:04 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

C67...just in case anyone wants to know.
It was a 10v 100uf cap.
another one of those "Taiwan" Cobras, if that matters.
Top of pagePrevious messageNext messageBottom of page Link to this message

2600
Posted on Wednesday, February 12, 2003 - 12:40 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

It's not "Taiwan", it's the calendar. Uniden moved production from Taiwan to the Philippines about 15 years ago. The 10-Volt electrolytics seem to have the shortest life span. Electrolytic capacitors just don't age gracefully. In 5 or 10 years you'll see the same problems in Philippines-made radios, too.

73

Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action: