I have a new Uniden pc78ltd anniversary radio that is smt, I can't find anywhere on how to lower the dead key and turn up the modulation on this radio? does it have adjustment pots to do a simple tune up, it came out of the factory dead keying 5 watts swings to 12 watts, I need to get the dead key down to below 2 watts, any help would be appreciated. Widowmaker
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Uniden pc78ltd dead key adjustment?
- Thread starter widowmaker1
- Start date
There should be a modulation pot. As far as AM carrier, most AM only cb radio's don't have a pot for this like SSB radio's or exports. You will have to add a combination of caps and resistors to get the dead key and swing to where you want it. You might try cbtricks.com . Being that it's an SMT board good luck soldering on that.
Peak out the coil in front of the final just like the old cobra 29 or uniden 78.
To lower the deadkey remove the large diode to the left of the modulation transformer. Add more diodes in series until you get the deadkey down to where you need it. I have not used the string of diodes but it should work fine. I vary the carrier of mine by varying voltage from the modulator. Basically what the string of diodes will do.
This is my radio. Ignore the big ugly choke attached to the orange wire. The diode will be where I soldered the choke to the board. Circled in blue. The coil I circled in red will reduce the carrier. Peak it out and lower the carrier with the diodes. Detuning the circuit is not the right way.
To lower the deadkey remove the large diode to the left of the modulation transformer. Add more diodes in series until you get the deadkey down to where you need it. I have not used the string of diodes but it should work fine. I vary the carrier of mine by varying voltage from the modulator. Basically what the string of diodes will do.
This is my radio. Ignore the big ugly choke attached to the orange wire. The diode will be where I soldered the choke to the board. Circled in blue. The coil I circled in red will reduce the carrier. Peak it out and lower the carrier with the diodes. Detuning the circuit is not the right way.
Looks like it's a bit much for my pay grade, lol!! for $80 I'll keep it in the box as a back up, I've just become not so excited about smt, going to find an older Cobra 29 with pots to turn and just run that with my old little 2 pill low drive, thanks for the information guys but, it's more than I'm capable of handling, for me to send it out to a shop & pay for shipping both ways and labor & parts etc. it's just not worth messing with, back to the old school radios for me, simple like me! Thanks again guys, I appreciate your input. Widowmaker1
Fortunately the diode you would remove isn't a surface mount component. It wouldn't be any harder than a cap & resistor swing kit on an old cobra 29.
I hear you though. Shipping a radio twice and paying for work doesn't make a lot of sense when you can get them on amazon for under 70 bucks.
I hear you though. Shipping a radio twice and paying for work doesn't make a lot of sense when you can get them on amazon for under 70 bucks.
that looks like the driver from the placement on the picture. I have been wanting to try a cap and resister on the middle leg to see if it would not create the swing mod just like a cobra 25 or 29 does. I have not had one of these radios as of yet but bet it would do the trick.put the pos of the cap towards the driver then solder the other leg to the circuit board where the center leg was soldered then put a 50 to 100 ohm resister across the area where the leg was to see if it did not make it swing as it should.
HEY WIDOWMAKER!!!
long time no talk.
glad to see you're still out here.
I will take care of that 78 for you, no charge.
just ship the radio to me and i will do it up right for you. (my address has changed obviously)
start a conversation with me here on the forum (it's the new way to private message) so we can work out the details if you're interested.
just click on my name over there on the left, and you should see the words "start a conversation" in the little grey box. click that and message me.
LC
long time no talk.
glad to see you're still out here.
I will take care of that 78 for you, no charge.
just ship the radio to me and i will do it up right for you. (my address has changed obviously)
start a conversation with me here on the forum (it's the new way to private message) so we can work out the details if you're interested.
just click on my name over there on the left, and you should see the words "start a conversation" in the little grey box. click that and message me.
LC
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I think they are good rigs. I am impressed with the receiver sensitivity. Not sure how it is in a mobile environment. I have the first IF in mine tapped to use an sdrplay for the rx. I can hear good wideband AM, use it as a panadapter to see the whole 11 meter band and even listen to SSB.
I was hesitant about the surface mount stuff but the 2016 cobra 29 ltd classic I bought was much lower quality. Even after the same alignment I give my other radios the rx was poor.
I've been wanting to try the string of diodes in series with d8 on a cobra 29 to lower the carrier. That with the keep alive circuit toll free posted here years ago is supposed to make a much cleaner waveform. Looks like its based on the 3 diode ultra modulation circuit from the 1950s.
543-Dallas,
If you want to read more about that mod, i believe they used to refer to it as the "dial-a-watt" mod, and there is an article in the back of either volume 28 or 29 of the Secret CB books.
LC
If you want to read more about that mod, i believe they used to refer to it as the "dial-a-watt" mod, and there is an article in the back of either volume 28 or 29 of the Secret CB books.
LC
thanks 9C1Driver!
normally i wouldn't put the free offer out there on the forum, but widowmaker is an old friend of mine who i lost touch with after I moved, then he moved.
I just had to take the chance that he might see the response since i know he doesn't get out on the forums too often.
you guys can bet that i'll be out here for a while. I tried moving away from radio in the past, sold my stuff, and still regret it to this day. I am on the younger side when it comes to CB techs, so I feel pretty confident that i'll be out here a long while.
as for the SMD stuff, it's the investment that is the killer. you spend all the money to be all set to solder and de-solder anything that may come across your bench, and then realize that you have to invest about the same amount for working on surface mount stuff.
to be honest i am still assembling my re-work station, so i don't tend to take on much of that type of work, but i do have to do it occasionally at work so i have to keep up on it.
I'll tell you this, if you don't have service literature for a radio that uses all SMD stuff, you might as well forget it. trying to trace circuits by following the PC traces will drive you batty!
uniden knew EXACTLY what they were doing when they put the kibosh on any and all service info for their CB line.
LC
normally i wouldn't put the free offer out there on the forum, but widowmaker is an old friend of mine who i lost touch with after I moved, then he moved.
I just had to take the chance that he might see the response since i know he doesn't get out on the forums too often.
you guys can bet that i'll be out here for a while. I tried moving away from radio in the past, sold my stuff, and still regret it to this day. I am on the younger side when it comes to CB techs, so I feel pretty confident that i'll be out here a long while.
as for the SMD stuff, it's the investment that is the killer. you spend all the money to be all set to solder and de-solder anything that may come across your bench, and then realize that you have to invest about the same amount for working on surface mount stuff.
to be honest i am still assembling my re-work station, so i don't tend to take on much of that type of work, but i do have to do it occasionally at work so i have to keep up on it.
I'll tell you this, if you don't have service literature for a radio that uses all SMD stuff, you might as well forget it. trying to trace circuits by following the PC traces will drive you batty!
uniden knew EXACTLY what they were doing when they put the kibosh on any and all service info for their CB line.
LC
I agree.
Yeah; the double side board traces and no schematic makes it hard to do.
The SMD magnification camera, the hot air solder/de-solder, and those nasty tweezers is enough for me to say 'no'. Rather work on a thru-hole board because I can still see the parts and get a schematic for them. Well; most of the time anyway . . .