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No voltage to Final Transistor,confused???HELP

I am have just made an additional "quick scan" through this thread...... and something is making me itch. With that.... I came back to express some thoughts. I may just be providing a good laugh....... but at the same time.... I am trying to apply some thought to this..... thought that I would apply if I were looking at this radio.

I have not seen anywhere above where you have specified.... so I am going to ask:

When you are making these measurements..... are you in AM or SSB?

here is why I ask.....

In AM the mode switch ties the AM regulator to the Vcc of the final and driver. When you switch to SSB.... the mode switch throws the full 13.8 VDC nominal to the Vcc of the final and driver.

IN addition to that......

The final (and maybe even the driver) are generally biased ( I am thinking) in a class where they are not BIASED until something is fed to them.

In AM you will have the carrier when you key up even if you are NOT modulating.

In SSB the balanced modulator "nulls out" the carrier so, if you are keying and looking at the base of the driver/final... there will not be anything there unless you modulate.

And, in fact... either AM or SSB you have to be keyed to see anything on the bases biasing the driver/final on.

Taking this from Lou's "big book" the final and driver will not generally have any bias UNTIL you "key up"(AM) OR "key up and modulate"(SSB). So if you are just turning the power switch on and looking for bias... I would expect that you would not see anything..... and since the final/driver are not biased on I would expect to see full 13.8 fed to them in SSB or a little lower in AM.

Just mull this over and see if any of this "makes sense" or "applies" to your case.

And if I am misguided I would welcome and appreciate a "swift kick" from someone who knows!!!!!!! :)

[Edited to add] more nonsense!!!! IF you are measuring in SSB..... you might want to use a scope to look for the activity on the base of the driver/final. It seems to me that the bias at that point would not be very large....and could possibly be loaded down by the meter.
 
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Hello, thank you for the writing back. What I am after, this is a AM 29LTD Classic,When I go to tune either RX or TX, I do not get any outgoing TX, does not move the meter on my extra radio besides me, and I am not getting any RX,no hiss or nothing. Put a new Audio Amp in, get the noise with the wet finger. I tune the cans to the Max voltage according to the Oscilloscope, watch for the Voltage line to increase in size then around this area, select the highest voltage and stop. I am waiting on a RF Sampler from China, and I also made one out of Lou Franklin's Understanding CB's book, but trying to understand it on the scope.
I bought a
Rigol DG1032Z Function Generator that does a bunch of good stuff, as I am still learning the Max on the scope, and what to put in on the Measurement side of the scope to watch for max, I try to watch the Yellow or Blue line increase in size and watch the Peak to Peak and try to use this for max reading. I guess I did not do enough reading and learning home to understand the Oscilloscope, I guess I just jumped to the Forum without figuring this out, just have a little more learning to use the schematics, and figure out where the Voltages to the Final Transistor come from.
Sam's Photofact's is the only manual that put's the Voltages in on the schematics, and the CB Tricks have a lot of stuff, but the schematics don't have Voltages in the schematics, that suck's. But I appreciate the help, as I did do all the basic's before I posted on this forum. I changed the Final and Driver, YES, they are good, I have a tester, I tried at least 5 or so Microphones, which is one of the leading causes of this issue,no RX or TX,. I guess I will have to find out where I get the voltage from on the Base, I am missing voltage to the Emitter and Collector. I check another CB, same type, and there is voltage at all the legs,as the second leg ( BASE ) has around 12+ Volts, and the other 2 has nothing, but the other radio's the work and align, has Voltage at the Collector,Emitter,and the Base....This is what I am after, as you cannot do anything with the CB without your Voltage. Thank you for you help, it is appreciated, but don't treat and act like I am a stupid, I understand and have done a lot more to this than you think. No hard feelings, but with my question, can we get real about it and not act like it is a stupid question, if you think it is a stupid question, then don't help, but I appreciate you all helping me, I am new here. Joined because I thought this site if full of smart and dedicated CBer's,and very smart repair people. #) years ago, I had a Cobra 2000, and a Kenwood ?? forgot. I shot skip on 11 meter, and made contacts on 10 meter as I had my Ticket to use, I am trying to get back into it, but I thought to pass time with this Covid crap,I would learn how to fix these things. Talk soon?
 
Rats!!!!! I was thinking that this was a Cobra 2000 thread. So obviously... no SSB. Here!!!!

But it is true that, to see something on the base of the driver or final... you would have to KEY the mic WHILE you are measuring.... and I would try it with the scope to see if the transmit strip IS producing anything.

The transmit oscillators will all be running but usually they are not passed down the transmit strip UNTIL you key up. And that bias for the driver and final is dynamically generated.... so if you are not keyed up....there will be nothing there.

But I have to say...... having 13.8 nominal at the driver final seems weird. Usually the AM regulator is dropped in voltage to accommodate the entire audio cycle modulating it..... strange.....
 
Ok, do you hear a Thunk from the radios speaker, when you turn the radio on?

A Cobra 29 has a "Green/RED" LED on the front panel - by the Channel Display...

upload_2021-2-24_18-10-12.png

When you key to go into Transmit, that RX/TX light turns RED
Does it?​
 
Yes pon the thump,and yes on the 13.8 on the power supply, as I can adjust the voltage on the Power supply,,about 2 volts or so each way. I am aligning the TX now. starting to get some static like the receive wants to start. I believe if I get to TX lined the TX way want to start, but I have the Signal Generator pumping 27.185 through the Mike socket, and going from here. Will update when I am done. Still only one leg on Final and Driver with Voltage..Update soon.
 
The 15 volts is what has had me scratching my head from the get go. Was wondering when someone would catch on to that.
 
Hello, I have it fixed,,,on the Cobra 29, you have the lower left leg ( BASE ) around 15 Volts. OK the other 2 legs get the Voltage from the 5 Volt line, as there is a YELLOW WIRE coming off of the Volume Switch. I wound up finding this HOT YELLOW WIRE came off of the board around near the back of the radio, next to adjustment of V5,in front of it. This wire heats up a section of the board and it heats up the other legs on the Final Driver, so I believe this is a 5 Volt wire to run the 5 Volt area of the CB Circuit. I went over that area with some flux and re heated the solder joints earlier when I first started of the radio as they looked like crap. I was thinking later that I remember having voltage at all three legs before, then remembered,,AH,check the wires, and sure, hard to see, yellow wire off,,,NOW THE OTHER 2 LEGS HAVE around 1.062 VOLTS OF POWER NOW, ____you have the lower left, ( BASE LEG ) at 15.45 Volts, and the Collector and Emitter are at 1.062 Volts,,so this is what I was up against, where is my Voltage to the other 2 legs, so in this 1988 Cobra 29 LTD Classic, the Yellow wire feeds the 5 Volt line and runs the Final Transistor, heats up the fuses at the top left of the radio, and heats up certain areas of the board of what is on the 5 Volt line, may have to look. I want to THANK YOU ALL FOR THE HELP, as I appreciate it, and aalso I, and every body now has a idea or a tip on a 1988 Made In China model. OK thanks again to all, A lesson learned, check the wire after you do a Solder over fixing all the 30+ year old JOINTS, ( sounds Have a great evening and day tomorrow, Mark good after this fiasco )...Thanks agin to all, Till next time ????? Eiaser to just pitch in the trash LOL,,Mark from Cedar Lake, IN. KB9GTB,,Peace.
 
Hey,one more thing, the wire I found went to another W hole, I found my manual and put the wire where it went. OK,,now,,the whole story, The repair was a AUDIO AMP CHIP,,TA722AP was the problem. I install a new chip, and then I had my voltage to my s legs of my final transistor,,,Now I have
 
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