148 gtl rx feedback

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callega
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Newbie
Posts: 2
Joined: Monday 7th Jul 2014, 23:15
First Name: Jean
Location: Brasil

148 gtl rx feedback

Post by callega » Tuesday 8th Jul 2014, 3:04

Radio Make and Model: Cobra 148GTL SN: 13011503
PCB Number: PC412
PLL Number: MB8719
Test gear available: RF Gen. Fluke 20MHz Dig Scope, 4 1/4 + 3 3/4 True RMS digimeter, RF probe, Freq Meter, Tektronics 10MH analog Scope, etc..
Symptoms:
Strong RX feedback when SSB selected (upper and Lower), S Meter goes full scale, even with Microphone removed.
Look like I have some IF amp to mic amp feed back.

What is working:
AM RX, SSB and AM TX.

What has been tried:

Did it suddenly happen ?: Yes

Anything else that may be of help?:
Some time ago, I had some ssb/am switch noise.
I saw R96 and R95 cutted...

callega
Newbie
Newbie
Posts: 2
Joined: Monday 7th Jul 2014, 23:15
First Name: Jean
Location: Brasil

Re: 148 gtl rx feedback

Post by callega » Tuesday 8th Jul 2014, 3:05

I forgot, I get strong microphony..
Edit:
I was looking the radio now, and have some more info.
Without mic, I have the feed back, putting smeter up. Even with zero mic gain, it´s very low, but it´s present.
With mic, If I put mic gain to zero, it stops the feedback, but I have a strong hum (like if it has no ground).

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