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help debugging brand new 148 gtl

9

9Lives

Active Member
Oct 3, 2012
182
6
28
40
I just got the radio today. On intent to widen bands and do some hi fi. I opened the radio immediately add the resistor for talk back and wired am power to the external... all its good so far side bands working better than I thought receive its ridiculously better than 29, to be at least. So I take it apart to do the mmmaul receive.. I instantly notice that the old version of the radio uses the older audio chip but I attempted to translate my self, usually not an issue. All is fine until c183 and 182 are different.

I took the radio and hooked it up and worked for a min. Then it started.
Radio dead key's fine
Did NOT modulate. (I can't tell if it's a modulation issue or audio)
Ssb still full swinging
Pa still works.

I UN did the mods I was uncertain about. Variable power, talk back.. same result..
I tried a different Mic. Same.
Can some one give me any pointers? I'm too close, it's about to go against the wall.

I got the radio from copper and let them do their peak and tune.. bull shit.. radio was keying way to high.
 

The new version 148's are very poor radio's that have been cheapened up so much. I have heard several, the only one that sounded ok to average was doing 8 watts PEP on SSB. As soon as the guy turned it up to 12-14 watts the regulator could not keep up and the audio sounded like crap. I would un-mod it and return it if you can. That or put it back to stock and dump it on E-Bay. Then look for an older 148, Grant xl, or Grant LT.

Copper is a necessary evil, I sometimes have to buy a mic, power cord, jumper, and so on from them. I would never buy a radio from them. As far as their "tech work" (lololol) I would not let them touch my toaster much less a radio. Good luck, hope you can work it out.
 
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Did you confuse the audio chip with the voltage regulator? All 148GTL radios use the TA-7222AP audio chip. The chip that was changed is the 8 volt regulator. Old radios had the 8 pin chip while new radios have the 3 terminal regulator. Audio chips are the same.
 
This one has td2003 or ta2003 it's behind the transformer. I agree it's nothing special but I'm positive I won't get what I pay for it. With alil love it can probably perform good enough to drive an amp..

I learned my lesson with them. I seriously think all they did was turn the am power and ssb power up. All the bias pots were locked in from the factory still.. rip off.

So it's that the general consensus? That it's a regulator issue?
 
There was one I couldn't find. 18 something...

There's on thing about cb I don't understand. I know that it produces a carrier and modulates inward tword 0. I use to not realize that. But what part makes it modulate? Is it the regulator?

If it were my audio then none of it would work including pa?
 
tr41/tr42 (the darlington pair) modulates the driver/final.

Kind of weird that on the new style 148 GTL's tr41 is mounted on the back chassis wall w/ the so239 instead of to the side of the transformer like in all previous 148 revisions.

If you only swapped/removed a few caps those should be easy to put back like they were. Double check for solder bridges ... How did you do the variable deadkey mod? I would suspect that modification first and check or undue your work there.
 
With all the info available on the internet and this forum about these crappy radios, I will never understand why people still buy them.
 
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I had always avoided the new front mic style 148's due to the bad reviews and trash talking but I recently picked one up to do hifi direct injected audio with and honestly out of the box it was as good if not better than any 30+ year old side mic 148 I've ever had my hands on at least on RX and stability and alignment right out of the box.

I modified it immediately to direct inject audio and bypass most of the audio circuitry so I never got to hear the TX audio stock.

YMMV...
 
I had always avoided the new front mic style 148's due to the bad reviews and trash talking but I recently picked one up to do hifi direct injected audio with and honestly out of the box it was as good if not better than any 30+ year old side mic 148 I've ever had my hands on at least on RX and stability and alignment right out of the box. I modified it immediately to direct inject audio and bypass most of the audio circuitry so I never got to hear the TX audio stock.
 
I bought it for that purpose too.

And the radio isn't that bad.. it does have to good points.

Ok I've got the problem narrowed down. It's not the regulator. The voltage checks. But the final is getting full voltage. The bias trimmer is only getting .01- .03 maybe? Seems to low?
I'm in the process of following the trace to see a difference in voltage. This is the China 148 gtl d. The schematic I have is a bit confusing.

Tr 41 and 42 are checking 12v on 2 pins 0 on the emitter I'm guessing? Should the base be lower?
Also the trimmer fire am power is ok. 0-6 volts.
The meter and dimmer lights up so eliminate that trace.
I hope this is the right track
 
I know that you can volt the driver wo screwing things up. If I did that could I bypass this whole problem?
 
Still got problems, I picked up another one from the "local cb repair...." if you call him that, I just score boogers off him, got another one of these for 20 bucks, it was off freq by 40 channels,,10 pin of audio chip was grounded hehehe

I got it going but every time I do the tx mods it jacks every thing up. Thus time it blew tr24, 2nd transistor in input circuit. I can't figure out what I'm doing wrong.
I just got my first scope today and I'm looking for a circuit to use for debugging but the sco pe sseems better for adjusting carrier and modulation.

Who ever that was who said they successfully wide banded this radio please help, every time I replace c101-108 it messes up the whole thing, are my caps to big? I'm subbing the 910pf for 1000pf, is this a prob?
 

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