| Author |
Message |
    
Darkseid
New member
Username: Darkseid
Post Number: 7
Registered: 2-2006
| | Posted on Wednesday, March 15, 2006 - 1:54 am: | 
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I have a Cobra 148 GTL with the mic on the side. I think it's made in the Philippines, the tag is pulled off the back, so not sure on that, it was a ebay deal for $45....
The radio keys down about 1-7W with a variable control, swings to about 12W. The clarifier is unlocked. And has the Poor boy channel mod for the 8719. It modulates just over 100%
The "problem" is when I speak into the mic it drifts off frequency. It will stay on frequency when keyed with no modulation, say If on 26.905 when modulating it drifts down to 26.902 ????
Is there a fix for this, or a way that I can align it? |
Jon666
Intermediate Member
Username: Jon666
Post Number: 397
Registered: 11-2003
| | Posted on Wednesday, March 15, 2006 - 8:26 pm: |
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are you using a coax fed frequency counter.
if you are it is not drifting, the
counter is only used for a dead key.
mo modulation
jon |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1304
Registered: 9-2004
| | Posted on Wednesday, March 15, 2006 - 10:35 pm: |
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i agree with jon666, dont trust the reading on that freq. counter when modulating.
if you want to be sure, go to SSB and get a radio check.
somone can easily tell if you are sliding off freq. when talking.
im willing to bet they say the radio sounds fine.
matt |
Darkseid
New member
Username: Darkseid
Post Number: 8
Registered: 2-2006
| | Posted on Thursday, March 16, 2006 - 2:10 am: |
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Forgot to mention, the reason I hooked it up to a frequency counter is from the radio checks on AM. I have been told it sounds like its off frequency and unintelligible.
Yes, I have been using a coax fed frequency counter. It does deadkey on frequency with no modulation.
Hmmm... Maybe it's not drifting. Could be something else...
It's 50 miles to the nearest cb shop 
Might be able to fix it, if I knew the procedures of doing it. If it's a big long list of procedures, its going to be a long trip to the cb shop lol. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1309
Registered: 9-2004
| | Posted on Thursday, March 16, 2006 - 6:24 pm: |
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seems to me that if you are deadkeying on freq. then the modulation shouldnt affect that.
the only thing i can think of is that the person who did the clarifier mod, used a power source for the clarifier that is dipping on modulation peaks.
this could cause the problem you are describing.
are you sure the power source for the radio has enough current? it should be a 5 amp supply at absolute minimum.
find the wire coming from the clarifier pot that has 8 volts on it, and follow it back to the PC board.
it should be soldered to the + side of C84.
if it is not, remove it and solder it there.
problem still there?
replace C84 with a new cap.
use one that is rated at 16 volts or more.
while you're at the parts store; pick up a 2200uF 50 volt (at least 35 volts) cap.
replace C172 with this cap.
also get a 680uF 16 volt (min.) cap and replace C18 with it.
these last two caps may not be "bad" in your radio, but it will operate much smoother after being modded like yours is, with the bigger caps.
do a google search for "148gtl clarifier mods" to find some diagrams which should prove helpful in finding the right wires etc.
try the first step (the correct power source for the clarifier) and post here if it worked.
then do the other cap changes, best to do these things in stages, checking the radio as you go.
good luck,
matt |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 97
Registered: 8-2005
| | Posted on Thursday, March 16, 2006 - 7:06 pm: |
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Wow Kid, you really know your stuff! Can I mail you my Cobra 2000?  |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1314
Registered: 9-2004
| | Posted on Thursday, March 16, 2006 - 9:03 pm: |
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thanks, i wish i knew my stuff.
i just know a lot about this chassis, having owned a lot of them, stared at a lot of them, and fried a few of them. (never actually fried one, but i have seen a few that looked "baked")
actually, i have to credit this forum for my increased knowledge of this chassis. when i first got on; i asked over and over for any "special" mods for this radio that werent already all over the net, and after a while i found more and more.
i have to say that Patzerozero has really taught me alot, and i would say that HE "really knows his stuff".
these are my favorite radios and i want to know them like an old mechanic knows a quadrajet carb.
now that im done with the "im no tech" disclaimer;
THANKS VERY MUCH for the compliment.
i may not be able to explain the theory behind all the complex circuitry inside these babies, but i am very steady handed, pretty darn handy with a soldering iron, and i take a lot of pride in anything i build.
in my professional life, i work with automation systems, and also do my fair share of fabrication and i feel like it all applies to radio in some way.
i love learning itself, and am always reading some sort of technical manual or something.
have a fine one,
matt |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2572
Registered: 7-2004
| | Posted on Friday, March 17, 2006 - 6:17 pm: |
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thankyou, kid, now if i could just stop getting me head stuck going through the door 
darkseid, how does it sound SSB? could be a combination of clipped limiter & other audio/modulation mods that are giving a 'scratchy' sound to AM XMIT. try backing mic gain down to the least amount of audio, replace limiter if needed, & see if you still get 'off freq' reports.
on AM, 3kHz off freq should NOT get you 'unintelligible' reports. it may not sound bad at all. i'd attack XMIT audio before freq troubles. |
Darkseid
New member
Username: Darkseid
Post Number: 9
Registered: 2-2006
| | Posted on Friday, March 17, 2006 - 9:29 pm: |
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Thanks for the help
Ok, I looked it over today, popped the hood up for a closer look lol. This radio is made in Malaysia.
I followed the wires from the clarifier, center blue wire goes to the pc board, One wire goes straight to ground, the other, + wire goes to the 3rd pin on a MB3756 IC Voltage Regulator ( i guess its a voltage reg.) I measured the voltage 3rd pin at 1.8 volts.
I found C84, it's 1000uf 16v
Did not find C172 or C18, maybe their under some glue...
I did see:
Q C2166
Q C1969
R31 clipped
C175 1000uf 16v
C173 10uf 25v
C176 47uf 16v
C179 1000uf 16v
I would think C172 would be somewhere in the area?
Maybe the Philippine and Malaysia 148gtl have different part numbers?
However, I hooked it up to a 12v power supply at 10 amps... And it worked today!!! Had good reports of it being loud and sounding great, this was with the covers off..... I did noticed bad soldering in the radio, some loose solder did fall out! I guess the previous owner didn't have a steady hand lol.
No chance yet to try SSB.
I will resolder the bad stuff later, need to know if I should soldered to the + side of C84? is this the same radio? I did look on the net about the clarifier mod, and this radio is hooked like one of the versions I've seen.
I'm still not sure what caused the off frequency modulation though? |
Jon666
Intermediate Member
Username: Jon666
Post Number: 400
Registered: 11-2003
| | Posted on Saturday, March 18, 2006 - 12:47 am: |
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it might have had a bad hair day.
radio problens are strange sometimes.
just keep using it.
jon |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2577
Registered: 7-2004
| | Posted on Saturday, March 18, 2006 - 9:18 am: |
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if increasing the power supply amps improved modulation(eliminated the scratchy, off freq sounding audio), that's a sign of possibly some power mods/high swing audio mods, or the original PS was just way too small. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1319
Registered: 9-2004
| | Posted on Saturday, March 18, 2006 - 9:43 pm: |
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i think pat has it right; in both his posts.
i could be wrong on the C172 part number. if C179 is near the rear right side of the radio, with the component side up and knobs facing you, then its the right one.
move the wire going to pin 3 of the MB3756 to pin 1.
matt |
Darkseid
Junior Member
Username: Darkseid
Post Number: 10
Registered: 2-2006
| | Posted on Friday, March 24, 2006 - 1:58 am: |
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Thanks for the help, so far replaced the big caps and some of the stuff as suggested. It seems to be sounding better than ever, Just for reference, C179 is near the right side.
Now I like to fix the cosmetics of it. |
Al_lafon
Intermediate Member
Username: Al_lafon
Post Number: 191
Registered: 3-2005
| | Posted on Sunday, April 02, 2006 - 12:39 pm: |
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Hello it's a blast how the guys here help one out. I tip my hat to ya! |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 24
Registered: 6-2005
| | Posted on Monday, May 22, 2006 - 3:13 pm: |
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May be L31 too,
I notice AM jumps around when keying up if L31 is not tuned right. |
