The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Shadow

Radio Make and Model: Cobra 148 Soundtracker PCB Number: 4A1099A Rev.08 PLL Number: MMB8719 Test gear available: power/SWR meter, multimeter, ext. freq. counter, hammer Symptoms: low RX. The wires from the RF Gain knob are sensitive to the touch. When I touch them, the RX increases (the more fingers...

Shadow

Hi guys. I've been looking around the internet for some good instructions for doing the IRF520 MOSFET mod on the cobra 25 but have not been able to find anything other than the cbtricks ERF2030 instructions. dtbradio has an excellent mod posted up for the Cobra 29 which I have done several of with e...

Shadow

Hey guys, wanted to know if anyone knows a way to increase the 'microphone gain' knob range on the Ranger RCI-2950 and/or the Cobra 148 GTL. The 148 ain't that bad, but the 2950 is just so low. Any help or suggestions is appreciated. I'm currently experimenting with the 2950 trying to get it to soun...

Shadow

Awesome! Thank you very much for the info 1096. Do you know if there is a way to do it on a 148 GTL?

Shadow

bump! anybody? anybody? Bueller?

Shadow

hahaha looks like i'm not the only one confused about this.

Shadow

Every since I acquired my first 148 GTL I have been afraid to do anything but a simple peak on it because there are millions of different versions of mods out there for it (just like every other radio). The problem is I like my 148 too much to experiment on it so I am asking if anyone knows of the b...

Shadow

This has been something I've wanted to do for some time now. I've done it on my Cobra 25 and it works well and I wanted to know if anyone knows how to do it on a 29.

On the 25, you decrease the value of the resistor in R76. I know I can get a power mike, but that's not the point. Any ideas?

Shadow

The Defpom wrote:Yeah, the tuning slug is the way that it is designed to be adjusted by, so try screwing that slug in to reduce the output power and see if that helps.

That was it, the tuning slug was too far out, I should have thought of doing this in the first place. Thanks Scott.

and thanks for the reply 222

Shadow

The Defpom wrote:Reduce the power output.

Hey Scott, thanks for the fast reply. I'm not sure what you mean by reduce the power output, do you mean to adjust the AM power via the tuning slug on L14 or is there something else as well?

Shadow

Radio Make and Model: Cobra 29LTD PCB Number: GEPC-060-M1 (Nov 2006) PLL Number: 29LTD 0445 Test gear available: power meter, SWR meter, modulation meter, multimeter, freq counter, dummy load Symptoms: Radio won't go over 45% modulation even when AMC turned up or limiter clipped. What is working: E...

Shadow

hey thanks man, i know that there is something else that needs to be done. I once got a cobra 29 from someone that had the same problem and it was an easy fix, im assuming this is along the same lines but gotta find the right thing to tweak.

Shadow

Hey guys, im hoping someone can help me out here. I recently unlocked the clarifier on my PC-412/MB8719 148 GTL using Ricks method (BTW, thanks Rick!) 1 Remove D52 2 Remove R44 3 Remove R174 and solder a jumper in its place. 4 Unsolder the red wire that comes from the Voice Lock pot from the PCB and...

Shadow

A few days ago I ran into a great deal. Someone was selling a virgin Filipino 148 in great condition and with all the accessories for $50 so I picked it up and started modifying it right away. Talkback, frequency conversion (hi and low), 10khz switch, variable dead-key and modulation, and now im try...

Shadow

I know this is a long-shot, but im letting my friend borrow my spare cobra 19 but I wanted to pick up the mic gain a bit because it's so weak. I don't have a power mic for him, and i've already opened up the modulation. If anyone knows where i can find the mic audio circuit and more specifically a l...

Shadow

I never knew radio shack even made a peak reading watt meter, are you sure its supposed to be peak reading? Yes, unless they had a switch on it to select between 'AVG' and 'Peak' just to confuse people, but somehow I doubt that Tandy ever had that much of a sense of humor. lol But yes, they made 2 ...

Shadow

Hi guys, I've got a Radio Shack power meter model 21-524 that will not read PEP watts. Everything else works great on it so I'm wondering if anyone knows of a part that goes bad on these things that keeps them from reading PEP watts. I opened it up and gave it the visual but I don't see anything out...

Shadow

speedracer6g wrote:Sure can!!

-instead of using a 4.7k use a 10k pot or 100k. set your gate voltage to about 2.7 to 3volts.

Hey Mike, since there is no C116 on the Cobra 25, where do you solder the other end of the pot?

Shadow

Hey guys, I got a question about the LED digital displays. Is there a way to know what part number I should look for in a display? There is a huge electronic parts distributor by my place and they have everything, unfortunately I don't know what I need... I need a display for several radios... all c...

Shadow

well i coudln't do anything without the help of others. This is a new venture for me so it's exciting to actually see positive results.

thanks again

Shadow

If I did, you would have first dibs. This is my only new virgin 148 so im sure you know how it feels

Shadow

Awesome! you guys rock. it was C117

Thanks a million!

Shadow

Radio was given to me, sat around for many years but looks like it had some good use before that. When i plugged it in, it's stuck on transmit... Radio Make : Cobra Radio Model : 29 LTD (taiwan) PCB number : PC-900AB PLL number : ??? IC number : D2816C What doesn't work : Radio is constantly transmi...

Shadow

Got it all figured out! Thanks to Buck, Rick, and everyone else who helped out. Replaced all the caps and now it's as good as new... in fact is practically is new

Shadow

Hey buck, thanks. I didn't even see the post here, but at the other forum.

Got another problem now. I cannot find any 330 uF or .47 uF at my local RS so i was wondering what i can use as a substitute if I can.

Shadow

I was about to ask the same question when I ran into this post. I'm also curious to know what kind of oscilloscope to look for.
Thanks

Shadow

I've got a bunch of replacement caps but they are all higher voltage than the stock ones, does that matter?

Shadow

Ill bet the house on this one. Don't mess with the audio chip, instead, replace all the electrolytic capacitors in the radio and it will come back to life. That radio is going on 30 years old and the caps are dried out. Cobra used cheap caps in the Taiwan model. I will dig up a list of their locati...

Shadow

Sure can!! -instead of using a 4.7k use a 10k pot or 100k. set your gate voltage to about 2.7 to 3volts. Do this by putting a voltmeter on left most leg of the mosfet final when looking at the face of the transistor. -remove C45 -remove C46 and install a 480pf capacitor. Call me blind, but I don't ...

Shadow

Actually L38 was already adjusted when I got the radio, the wax had been removed. Is there any way I can put it back to where it's supposed to be?

Shadow

Hey guys, does anyone know if there is a way to lower the dead-key on these PC-412 GTLs without compromising the peak output? It's bad enough that they only put out 20w max on AM so I'd like to preserve as much of that as possible. The radio already has a freq. expansion board and an unlocked clarif...

Shadow

Thanks for the help so far guys, I got the readings from everything but I don't know how to number the pins. could someone explain the numbering sequence on the pll and the ic?

thanks again!

Shadow

It would be best to let us have the PCB number. What is the part numbers on the IC bolted to the chassis. Hi Rick, i appreciate the help. Sorry for the delay but I got laid off last week and things have been kinda hectic. I updated my first post with all the info. The number on the PCB is PC-412AD ...

Shadow

Thanks for the details! I checked D55 and it looks fine. resistance in one direction, open in the other. I'm not sure where the audio chip is. im assuming it's one of the chips that are screwed onto the side of the case but there are 2 or 3. I've tried to read the schematic but i don't think I'm at ...

Shadow

Hi guys, i've searched on this topic but haven't found any threads with this specific problem so here it goes: Radio Make: Cobra Radio Model: 148 GTL (taiwan) PCB number: PC-412AD PLL number: MB8719 (8334 C06) IC number: MB3756 (8345 M67) What doesn't work: No TX (light comes on) no RX (light comes ...

Shadow

There's a way but I think that people want to keep it a secret. Here's how I did it. Connect the negative terminal of your speaker to the RX pin on the inside of the mic jack with a resistor in line. I used a 100 ohm because I like my talkback a little loud but i think 150 will be better for most ap...

Shadow

Does anybody know what exactly these modifications do on a cobra 29? - Change R123 to a 0.47 ohm resistor - Change R58 to a 2.7 ohm resistor - Put a jumper across D8{by audio transformer} - Change C71 to a 33uf 16volt polarized electrolytic capacitor - Put a 47pf disc cap across C57 - Put a 47pf dis...

Shadow

Hi everybody, I've got an old Realistic TRC-467 im modding for a friend and it has no PA. Could anyone tell me what my options are for doing a talkback mod on it?

thanks!

Shadow

Terrain, buildings, and trees (among other things) have a huge effect on your TX distance. What is between you two when you are only getting 3-4 miles?

The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Search found 39 matches

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