Hacked Cobra 148 GTL

[Onryolbastard]

Hello. I need help with a hacked Cobra 148 GTL I just bought. I removed the lids to inspect it and found some interesting things. Someone removed the wires from the bright/dim switch, cut the D52 diode, cut the R113 resistor, and there is a cut white wire sticking out of the circuit board that doesn't go anywhere. Is this some sort of mod? Or is the bright/dim switch bad and they bypassed it?

 

[NZ8N]

R113 (10k) is the resistor that turns on TR21 which does 2 things, 1st, it unbalances the Balanced Modulator (IC 3 AN612) which causes it to provide the carrier when in AM TX, and passes mic audio from the mic preamp circuits through R114 (27k) and C46 (.022uF) to the AF input pin of IC6 (TA7222P) the main audio chip.
D52 is one of the series diodes that if cut or removed, tells me that they have the Clarifier unlocked, so the TX frequency follows the RX frequency. They have most likely taken the wire that goes to the "high side" of the Clarifier pot in the front of the radio, and moved it to a constant +8v source.

 

[Onryolbastard]

Should I just leave it? Or should I take it to my local CB shop and see if he can put it back to factory settings. It's a damn mess. Looks like it would be a P I A to out back.

 

[Onryolbastard]

Meant to say " put back". Stupid auto correct.

 

[NZ8N]

I had a better look, R131 is the vertical resistor that is cut behind R113 (not cut) which is laying down. This disables the AMC sensing transistor. It should be resoldered or replaced to re-enable the AMC adjustment control. There may be other components cut too. Like check to the right a little bit, over closer to the wall, TR24.

As to the Clarifier mod, that's up to you. I prefer to have my transmit and receive frequencies in the same place, and used to do this to my radios, but not "clip and snip". I desoldered the components like D52.

 

[Onryolbastard]

It would be cool to know where the blue, pink, 2 black and the 2 white wires go. I've seen pics of other 148 GTL boards and I've never noticed any wires soldered to the board like that. And I assume the RF meter bulb isn't supposed to be wired in like that?
As far as D52 and R113 are concerned, I will let someone else mess with those. If I didn't have my glasses on and my magnifying glass I would have never noticed them. They are to small for me to mess with.

 

[w9cll]

You have no idea what damage has been done to the radio, personally I would cut bait and unload that radio and buy a different one.

 

[Handy Andy]

To help with sorting out some of this...​

The PLL stuff? most can be easily removed, unsoldered - from the board with some "re-bridging" of traces that might be necessary.

Looks like White Wire (as) AMBER Arrow was a do up for Pin 10 extra channels - Got 8 volts from Power Filter cap heading to Pin 9

One BLACK Wire Brown Arrow went to this Pin 10...
The PINK Arrow Pink wire went to a channel Selector wire to Pin 11
Another Black Wire heads to Board ground by front of board by Channel Selector.

Removing these wires will make the Radio work closer to stock , once you undo these wires check your work for shorts and any repairs, you soudl have NORMAL selector of channels.

The biggest work and recovery, if the PLL does fire up after this, is done, to me this work looks like a 5Kc jump and possibly a extra bank of channels if the VCO could be made to lock - looks like the VCO was left alone so you may have a keeper is the VCO is still working and the PLL can work it.

 

[Onryolbastard]

What does PLL, VCO, and 5Kc stand for? None of these wires go back to the bright/dim switch? Except for the black wires?

 

[Handy Andy]

Do you want to return it to stock or use it in it's current condition?

​

It's apparent you may be in over your head, the area I pointed to earlier is the PLL - the IC that does the work to make the Channels.

The VCO is the other part - the PLL uses it to generate the FREQUENCIES to make the Radio work and so you can transmit and receive.

Follow Pink wire to switch with BLACK wire already soldered - that more than likely is a 5kc "shift" - Black wire I presuming is ground...

Where the Pink, White and Black wires are at the row of pins, is the PLL IC itself - they put these wires in there, that normally are not there - to make it do things that only the installer, knows how to operate.

We see this area, knowing what the PLL and the area around it should look like - we can tell you something thins are done to "add" stuff - but not how the installer did them or why it was done a particular way - more than we can only guess at.

The Black wire to Black wire switch is your Pin 10 "band" switch - extra channels if the VCO could fire on them.

So do you want to return the radio so it can work normally or you just trying to find the guy who did this to the radio so you can get the correct owners manual?

 

[NZ8N]

The switch you have removed from the faceplate with black wires, basically grounds Pin 10 of the PLL, thereby causing the PLL to jump up by 640 KHz, or 64 CB Channels. Channel 1 then moves from 26.965 to 27.605 which people refer to as being Ch 60. The Pink wire shifts the PLL in steps of 320 KHz, or 32 Channels. This appears to be soldered to another switch on the face.

As to their original hookup, there are 2 sides to that Bright/Dim switch, one side of the switch used to dim or brighten the meter bulb, the other side dims or brightens the LED Channel indicator.

I haven't looked at a 148 in over 20 years, having got out of the CB repair business, so the info for their original locations for Bright and Dim on the main board, I have long since forgot.

 

[Onryolbastard]

Thanks for helping me Andy and NZ8N! My goal is/was to put the 148 back to stock. I thought the wires that are soldered to the board were just disconnected from the bright/dim switch, and reconnected to different areas. But the pink wire is connected to the tone hi/low switch, now I’m even more confused. So that switch must be part of the mod also. the top lid has “Treeclimber” written on the inside, and the date 1/17/16 written on it. I have no idea what the hell that means. I was shopping for a Uniden Grant XL or a Cobra 148 GTL and this came along 1st. Kinda wish I would have skipped it now. Maybe I will just try using it the way it is and see what happens.