Help Restoring A 142 GTL with A 2SC2078 Driver Mod

[LeapFrog]

Hello everyone, I have a 142GTL with a 2SC2078 rf final installed as a driver!

I have a 2SC2166 And would prefer to return the radio back to original spec.
Here is the 100 Ohm Bias Resistor, And the Trace goes to pin1 of the 2166 (base), to junction of c215 i think.
[photo="medium"]4231[/photo] .
Measured:
[photo="medium"]4232[/photo] .
The numbers did not come out in the photo, but it is a 2SC2078 installed as a driver "pushing along" a 2SC1969.

And the RF Final could be a fake, as the radio only does 2-3 watts @ 95% mod!
[photo="medium"]4233[/photo] .

& Yes the radio is ready for a cleaning & a re-cap, I know lol.

To install a proper 2SC2166 driver in this rig, pull the 100 Ohm resistor, & set the bias to FSM specs.?

I need a little help/advice on things to look for that may have been changed.
What key components may be modified from original value in regards to the bias on this radio.

I do not have a Sam's Photofact on this one, perhaps a FSM for the Uniden PC-385 series boards exists online?

I am absolutely lost on how to set the bias! I've never done that before!

Also I found 50mA and 100mA online but I'm not certain which for which i.e. 50mA for the driver or for the final? !

Has anyone seen this mod, and know what to check to revert back to stock?

I here the 2078 has more gain than the 2166 (haven't read the datasheets in a bit), I just want a factory radio now, with no-wack-pack mods..

Best Regards
-Leap

Here is a snap of the schematic:
[photo="medium"]4234[/photo]

 

[LeapFrog]

Also guys I'm wondering what wire is messed with when they "volt the final". Thank You

 

[sonoma]

this info should give you all the answers to volting the final and the npc mods.

http://www.cbtricks.com/members/kd6tas/npc-2.htm

 

[Robb]

Hello everyone, I have a 142GTL with a 2SC2078 rf final installed as a driver!

I have a 2SC2166 And would prefer to return the radio back to original spec.
Here is the 100 Ohm Bias Resistor, And the Trace goes to pin1 of the 2166 (base), to junction of c215 i think.
[photo="medium"]4231[/photo] .
Measured:
[photo="medium"]4232[/photo] .
The numbers did not come out in the photo, but it is a 2SC2078 installed as a driver "pushing along" a 2SC1969.

And the RF Final could be a fake, as the radio only does 2-3 watts @ 95% mod!
[photo="medium"]4233[/photo] .

& Yes the radio is ready for a cleaning & a re-cap, I know lol.

To install a proper 2SC2166 driver in this rig, pull the 100 Ohm resistor, & set the bias to FSM specs.?

I need a little help/advice on things to look for that may have been changed.
What key components may be modified from original value in regards to the bias on this radio.

I do not have a Sam's Photofact on this one, perhaps a FSM for the Uniden PC-385 series boards exists online?

I am absolutely lost on how to set the bias! I've never done that before!

Also I found 50mA and 100mA online but I'm not certain which for which i.e. 50mA for the driver or for the final? !

Has anyone seen this mod, and know what to check to revert back to stock?

I here the 2078 has more gain than the 2166 (haven't read the datasheets in a bit), I just want a factory radio now, with no-wack-pack mods..

Best Regards
-Leap

Here is a snap of the schematic:
[photo="medium"]4234[/photo]

Yup; put the radio back to specs, as per the schematic.
I would too.

 

[LeapFrog]

Can you give me a brief overview of how biasing this radio would go down, I don't have a clue. (No FSM)

 

[sonoma]

defpom has the alignment wrote out on his site. shows the complete alignment of the radio

http://www.radiomods.co.nz/alignments/pc385align.html

 

[LeapFrog]

Sweet, Thanks Sonoma!

73

 

[sonoma]

Leapfrog just to let you know I do the mod for AM on all of my 142 and 148 radios. after I recap them and then make sure all is aligned properly I will do the mod I left you from Bill. the radios sound good with this mod. at least they do if done right.
some people like the mods and some do not.
just my 2 cents worth.

 

[LeapFrog]

Leapfrog just to let you know I do the mod for AM on all of my 142 and 148 radios. after I recap them and then make sure all is aligned properly I will do the mod I left you from Bill. the radios sound good with this mod. at least they do if done right.
some people like the mods and some do not.
just my 2 cents worth.

I value your input on the subject Sonoma I am certain it comes down to how the person does the mod (what else may have been done to the rig beforehand), sometimes the NPC mod work for the better & sounds great (as apposed to just a nixxed amc) it's all about the setup and how the radio is operated. Am I right my man? That mic gain knob can make or break some setups!

I still need to make sure that everything is factory, & then I will make sure it's linear in the final section & not class C in AM. Looking it over I can see if any parts have been recently changed, a dust layer was left for me inside the rig, courtesy of the previous owner.

The 100 ohm resistor on the pc board worries me, I haven't spent much time looking over the schematic but I hope it's just an add on part, and not a replacement for a factory resistor, some of these Cobra radios have parts on the solder side of the board, and hardly any notation (if any) of their existence in the service manual, let alone lack of any markings to indicate that a part belongs their in the first place.
*Shaking my head ..like NO!!! WHY!!!

r204 was clipped, I replaced that with a 680ohm resistor as per schematic ,
and I was able to re-solder (save) r131(i think) which I also found clipped.

So far most of the radio doesn't look too bad, thanks again guys!
73
-Leap

 

[sonoma]

I have 2 142 radios for my personal use and both are different on the solder side as far as parts added. the radios had not been touched inside when I got them so the addons must be factory. it has been a while since I did any thing to them. just remember extra caps and resisters on them. kind of like the 139xlr radios having extra parts on the solder side of the boards. think some of the radios had changes on them when they came out to correct some thing they would find after the 1st production runs.
who knows for sure is the hard answer to get. hope you get your working as you like it.

 

[Robb]

I usually end up pulling npc mods out of radios because owners get bad reports when they try to use them in SSB mode. The second the AM limiter is pulled, it is game over for SSB - IMO. SSB radios really don't do AM as well as am dedicated radios anyway. Lot of the locals have been asking to set their radios straight so that SSB can be used with confidence.

 

[sonoma]

when I do any npc mods I do the part that does not effect SSB. the mods I due is for AM only since SSB on these radios works as it should when stock.

 

[LeapFrog]

I better check for pulled limiters this thing was just able to hit 10-12 watts average not PEP on ssb mode, WOW that is absolutely screaming & towards the max end of what I've seen a 1969 final do, so now I know that the final is probably real and a limiter is pulled somwhere.

The AM modulation looks clean on the scope, but if I scream (or crank mic gain) I watch the needle swing backwards on my AVG reading meter, so I know something else is not right, the dead key is under 3 watts and it swings backwards @ 13.8 Volts! OUCH!

I know from what I have read, some mods effect ssb audio, & some do not, it's all in what was done and how of course i'm just stating the obvious.

Thanks Again Guys
-Leap

 

[Robb]

Peaking the TX coils yields a real swinging radio, so that is what I recommend to others and do the most often. The 1969 final will often put out 16-20w when peaked well.

 

[LeapFrog]

Peaking the TX coils yields a real swinging radio, so that is what I recommend to others and do the most often. The 1969 final will often put out 16-20w when peaked well.

20 watts AVG, or PEP because If I did the math (or had a PEP reading meter) I would barter to say this radio is doing 20 watts PEP SSB already, just have to get AM sorted and look for disabled ALC/AMC.