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Cobra 148gtl on USB/LSB the famous garble problem

D

dss56

Active Member
Sep 27, 2010
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Hi i received a 148gtl and had some problems the tone and brite switch broken fixed and ok.

Problem is AM is perfect but both ssb are garbled motor boating.
I noticed on AM when talking the lite in meter seems to be ok.
When on ssb the meter dims some as you talk.

the radio has plenty of am and ssb power. Tr 24 was removed but i reinstalled a 2sc945.

So the ssb is garbled and I tuned the radio to most of the specs from an owners manual and other info from the net.
148 is from maylasia so its an oldie would like to get the ssb fixed.

might try the regulator replacing and see what happens.

I know there are many post on this with suggestions but not many replies with a good fix.

I tried tightening the screws on the board to chassis and nothing.

So with the meter light dimming a bit might be the constant 8 v from the regulator. I will check that later tonight.

Any suggestions on a fix?
thanks
 

Has the Electrolytic caps been changed?

The age of the radio usually means 10 + years old and original parts - you're on borrowed time. You get symtoms like this - at least if you're motor boating, that's means the regulator is "crowbarring" as in trying to regulate, but the load is too great.

This usually means that the radio needs a "Re-capping" and can also include the Electrolytic caps used in the COUPLING of stages. One stage shorts to the other stage and bias instability ensues...
 
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The Malaysian 148 is the same as the earlier ones with the exception of a trace on the regulator. If I remember you need to make a cut and put a jumper. I will try to find it in my files. Unless someone else finds it first. I have done several in the past and it fixes it 100%
 
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KneeBiter

I will try the mod tonight and let you know if it helped.

Again thanks so much for the info and video.
 
I hope I tried every alignment and tweaking up and tweaking down the power to see if it would help and nothing. Like I said AM is fine when on ssb sounds garbled and the front meter light dims when talking So I think it is a power problem and hope your video fix will work.

thanks Bob In Boston
 
Kneebiter

I went down to shop and tried the mod with cut trace and jumper and still no difference. Also changed out c172 a 1000V @25volts. As someone else suggested.

sounds like the old motor boating very raspy. I have a Meter with audio monitoring and I plugged in a head set to monitor and also another ssb washington radio and sounds like crap on the ssb.

With the mod the front meter still dimmed when talking so gotta look further. Cant get any good info as CBtricks has been down the past 9 days.

thanks Bob
 
dss56,
Try installing a .1uF mylar cap at location C136. (It is very near where you placed the jumper at the J44 location)

73
David
 
Dmans

I did add the 136 cap and no good results.

This radio was worked on by someone else like tr 24 removed i re installed the 2sc945.
Wires were cut and other things out of wack. So as I re tuned the radio and got most aligned i noticed the ssb motor boating very raspy. I have tried a few things like yours and a few other suggestions. I'm just going to button the radio up and return to customer.
I hate getting radios like this in for repair, hard to tell what was done.

thanks for the info/help
 
Sounds like one of mine that has the poor man's channel mod. Makes sideband unstable, so I'm told. The limiter was clipped and blasted AM, but ssb was terrible. Before the final blew it became really unstable in RX and TX. AM went weak.
 
This radio AM is fine no channel mods, no final replacements originals. Just cant seem to find out what is causing the lousy ssb audio
 

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