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2sc2078 vs 2sc1307
- Thread starter handyman-56
- Start date
If I had a 1307; I wouldn't waste it by putting it in a radio like that.
They are rare - if it is a real part and not a phoney.
They are rare - if it is a real part and not a phoney.
It looks like the 2SC2708 is a driver transistor as it is speced as having 4 watts out with 0.2 w of drive for a gain of 13dB whereas the 2SC1307 is a final speced at 13 watts out with 1.4 watts drive with a gain of about 9dB or thereabouts. Short answer is no you cannot simply drop one in as a replacement. The long answer is it may work but power output will likely not be the same due to different gain figures. I haven't even looked at the impedances of each.
ok i check my 2sc2078 and he's good. My problem my trc-430 don't have output modulation, no watt and the swr meter don't move. But when i check with another cb near, i cant ear my voice when i transmit with my trc-430. The cb receive well.
ok handyman, let's back up a bit.
I want to help you along, but some advice is going to come with it.
You entitled this thread 2sc2078 vs 2sc1307, which to us implies that you have already done the troubleshooting work to isolate the problem to the driver and final section of the radio.
You listed the reasons you thought it was the final that was the culprit, but none of those steps included actually eliminating any of the other possibilities.
So you are already way ahead of yourself, and usually when a problem starts out being described incorrectly, you don't end up getting the help you need.
so, a better title to this thread would have been, "TRC 430 no transmit" because thats all you really know right now.
Did you check the mic?
is there an indicator on the radio that tells you that you are actually going into transmit mode when you key the mic?
if so, is it changing when you key the mic?
If all that is ok, then the next step is to check the voltages at the driver and final.
we will stop there so you can do this step.
you are lucky with this chassis is there is a good amount of info on it:
http://www.cbtricks.com/radios/realistic/trc_430/index.htm
that should be enough info to get you started, or enough to get you in trouble. LOL
good luck
LC
I want to help you along, but some advice is going to come with it.
You entitled this thread 2sc2078 vs 2sc1307, which to us implies that you have already done the troubleshooting work to isolate the problem to the driver and final section of the radio.
You listed the reasons you thought it was the final that was the culprit, but none of those steps included actually eliminating any of the other possibilities.
So you are already way ahead of yourself, and usually when a problem starts out being described incorrectly, you don't end up getting the help you need.
so, a better title to this thread would have been, "TRC 430 no transmit" because thats all you really know right now.
Did you check the mic?
is there an indicator on the radio that tells you that you are actually going into transmit mode when you key the mic?
if so, is it changing when you key the mic?
If all that is ok, then the next step is to check the voltages at the driver and final.
we will stop there so you can do this step.
you are lucky with this chassis is there is a good amount of info on it:
http://www.cbtricks.com/radios/realistic/trc_430/index.htm
that should be enough info to get you started, or enough to get you in trouble. LOL
good luck
LC
I check the voltage at the final drive at the collector i have 11.8 when receiving but when i transmit there nothing
ok, so if the voltage on the final is changing from 11.8 (a little low, should be 13.8) to 0 on transmit, then at least we know the radio is switching from receive to transmit when we key the mic.
take a look at the schematic http://www.cbtricks.com/radios/realistic/trc_430/430_print.htm
and find Q305 and Q307 in the lower right hand corner.
Q305 is your driver, and Q307 is the final.
So you said that you have no collector voltage on the final (Q307) on transmit.
The voltage for the collectors of the driver and final both start at T201.
you can see that there is a direct line from the power switch to the bottom of T201, and the voltage goes from there, through T201, down through D301, to the collectors of the driver and final.
yes, the voltage for the driver has to go through R318 first.
since this line has voltage on receive, but not transmit, we know that there is something along this path that is shorting this line to ground only on transmit.
the first culprit would be the driver transistor itself (Q305)
so remove this transistor and check it using the diode function of your multimeter.
you might find that it is showing a short between two of the leads.
If this is the case, you can probably just replace it, and be back up and running.
if it checks good, then the next step is to start looking for branches off this voltage line that might have a part shorted to ground that only shows its face on TX.
The first place i would start looking would be D203 and Q309, just because they are the first parts on the one branch that comes off this line.
we'll stop there for now.
post your results and we'll go from there.
LC
take a look at the schematic http://www.cbtricks.com/radios/realistic/trc_430/430_print.htm
and find Q305 and Q307 in the lower right hand corner.
Q305 is your driver, and Q307 is the final.
So you said that you have no collector voltage on the final (Q307) on transmit.
The voltage for the collectors of the driver and final both start at T201.
you can see that there is a direct line from the power switch to the bottom of T201, and the voltage goes from there, through T201, down through D301, to the collectors of the driver and final.
yes, the voltage for the driver has to go through R318 first.
since this line has voltage on receive, but not transmit, we know that there is something along this path that is shorting this line to ground only on transmit.
the first culprit would be the driver transistor itself (Q305)
so remove this transistor and check it using the diode function of your multimeter.
you might find that it is showing a short between two of the leads.
If this is the case, you can probably just replace it, and be back up and running.
if it checks good, then the next step is to start looking for branches off this voltage line that might have a part shorted to ground that only shows its face on TX.
The first place i would start looking would be D203 and Q309, just because they are the first parts on the one branch that comes off this line.
we'll stop there for now.
post your results and we'll go from there.
LC
Dont take this the wrong way.
You might be better off getting another radio.
That radio is cheaper to buy a used one than to fix it.
What are you powering it with?
You might be better off getting another radio.
That radio is cheaper to buy a used one than to fix it.
What are you powering it with?
You cannot simply connect your meter to the collector of an RF transistor and attempt to measure the voltage on TX. The RF output, if any at all, will throw the meter WAAAAY off.The point where DC goes into the transistor is also the point where RF comes out. It may read hundreds of volts or simply nothing at all. As long as the point where you measure is isolated from the RF you are fine but if you attempt to read the voltage directly on the transistor lead you will get erroneous readings.
well CK, i know im walking out on a slim limb by disagreeing with you on anything RF related, but I have been measuring the DC voltages on transmit on drivers and finals for as long as i can remember.
Why would service manuals list a "correct" DC voltage for the collector leg of a final in TX mode if you could not attain that measurement?
http://www.cbtricks.com/radios/realistic/trc_430/430_tranv_ch.htm
am i missing something here?
It's been known to happen LOL.
LC
Why would service manuals list a "correct" DC voltage for the collector leg of a final in TX mode if you could not attain that measurement?
http://www.cbtricks.com/radios/realistic/trc_430/430_tranv_ch.htm
am i missing something here?
It's been known to happen LOL.
LC
The DC voltage is fed to the collectors thru an inductor. This inductor passes the DC but prevents the RF from flowing back into other circuits and the power supply itself.It is the solid state equivalent of a tube plate choke. If you measure the voltage on the supply side of the inductor all is fine since there is minimal voltage drop thru it. If you attempt to measure the DC voltage directly on the collector lead then the RF can and usually does affect the meter. Check out some of those TP,s (test points) and I am sure you will find that on the schematic they are located on the supply side of an inductor and not on the collector lead itself. It will also depend on the meter that you use to a degree. Most hobbyists have a simple meter that is not immune to RF present on a DC line. I have had an analog meter pin on the 50 volt scale when accidentally measuring the DC collector voltage with 4-5 watts of RF present when only a nominal 12 volts was present. Not sure what my Fluke 376 does as I have not tried it.
thanks for the info CK.
I guess i must have one of the lucky DMMs that does not get affected by the RF.
Im going to do some experimenting tonight with a few different meters just so i can see the effects of the RF on them.
This is also going to give me a new subject to read about, so thank you for that too.
LC
I guess i must have one of the lucky DMMs that does not get affected by the RF.
Im going to do some experimenting tonight with a few different meters just so i can see the effects of the RF on them.
This is also going to give me a new subject to read about, so thank you for that too.
LC
As I said some meters are fairly immune to RF while others go nuts. Most cheaper analog and some DMM's do not handle RF very well but since it is hit or miss it is best to measure the voltage on the supply side of the collector inductor to avoid any possible errors. I suspect that since my Fluke 376 has very high immunity to noise pulses on the AC/DC line it is connected too that it has high immunity to RF present on the line. It's a REALLY good meter that will read AC or DC current thru the clamp on jaws which is a GREAT feature as most do not read DC current without breaking the connection and inserting the meter in series. It's good for 1000 amps AC or DC that way or up to 2500 amps AC with the iFlex flexible current probe so I am all set for working on CB's with it. LOL
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