Cobra 148GTl only static and no transmit.

[Skyrider]

Hello everyone,

I received this 148GTL from someone with a bunch of ugly hack jobs done to it. The first thing i did was to undo a nasty free-band mod someone did and restored the original functionality of the front switches (nb anl etc) and fixed all the traces on the PLL. I plan to undo all of this mod stuff until i get the radio working right again,

The radio does not go into transmit mode, ive checked and the mic wiring looks fine. The LED stays in green but the receive audio does cut out. The only time the LED changes at all is when i put the radio in PA mode and it blinks off when keyed.

The receiver seems to be alive and is receiving static, but when i keyed up a walkie talkie next to it it didnt pick up my signal. Next using my signal generator and frequency counter i determined that the radio is picking up signals out of band and it seemed to only want to pick up stuff in the range of somewhere in between 27.485-27.505. Sounded pretty distorted.

Next is a weird slider/clarifier mod. I had completely missed this until later on. Il provide what was done so perhaps someone can tell me what else i should look for etc so i can undo the mod and restore the circuit to original.

Heres what i found.

*They added a double stacked pot and theyre connected together and one of the connections between them has a resistor. Ive never seen anyone use two pots like that for one of these mods.

*Off the double stack pot, Orange lead connects to one side of R44. The other side of R44 is clipped off.
*From that same side of R44 a lead connects to pin 1 of IC4.
*The blue wire of the pot was soldered to D51.
*And the red wire is still going to R175. which is 2.2k ohms.
*R174 is gone but not jumpered.
*D75 is clipped. Theres a spot for D52 right next to it but i dont know if that diode was originally never there or if it was removed.
*D53 has its anode connected to the can of a coil through a choke.

EDIT: VR5 is also gone.....

Anything else i may have missed? Could this mess be the sole cause of my radio not wanting to transmit, and my strange receive problems? Or should i expect more problems still after undoing this?

Thanks for all your help!

 

[Skyrider]

Ive restored most of the original components to undo the modification except for VR 5 and the 1n4148 diodes.

After that i proceeded to go ahead and go through the alignment procedure. Im having problems adjusting things to were theyre supposed to be according to the manual.

After adjusting L19 for 3.1v on channel 1 on channel 40 i got around 4.6 volts instead of the 4.2 volts recommended by the manual.

Adjusting L20 didnt seem to show much of a difference on my oscilloscope.

While adjusting L23 for 34.985 mhz i wasnt able to get up that far no matter were i turned the coil. I think the furthest i got was something like 34.845 or so. Same goes for L22 and L59.

I havent bothered to go any further as of yet.

The radio DOES go into transmit now, but there is a bad squeal that sometimes goes away if i poke around near teh PLL with my finger. The squeal also appears through the speaker on SSB half of the time.

 

[Skyrider]

I think i found the final piece of the puzzle here, at least when it comes to this mod.

I completely missed a VERY important detail. Someone swapped out the original 11.325 crystal (x3) with an 11.178. Well that explains a whole lot!

Anyone know were i could get one?

 

[radiohobby]

If you haven't gotten the crystal yet you might try getting it from Cobra. I used to buy parts from them when I couldn't find them at my local electronics parts store. They were always very fair on prices but it has been a lot of years since I have dealt with them so I don't know if they still do direct sales or not.