welcome to the forum David!
im guessing here, but what is the voltage on the PC board trace where TR23 connects to D21?
you should read 8 volts DC here in both RX and TX modes.
also, while doing your testing, set VR4 at about halfway. that way you are sure that some modulation should be getting through. you can re-set it once you get it fixed.
another test you can try is to put your voltmeter on the cathode (banded end) of D8, and key the mic. you will read about 13 volts DC or thereabouts.
now, with the voltmeter still connected, whistle or yell into the mic and see if the voltage starts jumping around.
you can also measure the DC voltage on each leg of TR17 and TR18, and compare them to the charts in the service manual here:
http://www.cbtricks.com/radios/cobr...st/graphics/29ltd-st_29wx-st_sm_pg12_pg34.pdf
I know these are kind of random tests, but their results will help track down your issue.
while you are diligently staring at the radio waiting for forum replies, try to confirm all of the things in the radio that DO work. does the squelch operate normally?
does the radio receive actual signals or just static? etc...
you can also use that voltage chart to start going through the radio comparing voltages on the audio amp, and any other transistor you decide is worth testing.
this is to help keep you moving and sometimes doing these things can help you stumble on your culprit, even if by accident.
do you have an external SWR meter?
if so, put it in line between the radio and the antenna/dummy load and set it to the CAL (calibrate) position. now turn the knob on the meter all the way to the left and key the mic.
while TXing, turn the knob until the needle sits about center of the meter.
now start yelling and caterwauling into the mic (dynamike all the way up of course) while watching the needle.
did it waver at all? any movement is a good sign.
post back after you mess with it a bit and try to give us a detailed description of what you encountered. the more detailed you are, the better responses you will get.
i am hopeful that something you notice will perk an ear of one of the gurus here who might be able to lend a hand.
good luck!
LC
im guessing here, but what is the voltage on the PC board trace where TR23 connects to D21?
you should read 8 volts DC here in both RX and TX modes.
also, while doing your testing, set VR4 at about halfway. that way you are sure that some modulation should be getting through. you can re-set it once you get it fixed.
another test you can try is to put your voltmeter on the cathode (banded end) of D8, and key the mic. you will read about 13 volts DC or thereabouts.
now, with the voltmeter still connected, whistle or yell into the mic and see if the voltage starts jumping around.
you can also measure the DC voltage on each leg of TR17 and TR18, and compare them to the charts in the service manual here:
http://www.cbtricks.com/radios/cobr...st/graphics/29ltd-st_29wx-st_sm_pg12_pg34.pdf
I know these are kind of random tests, but their results will help track down your issue.
while you are diligently staring at the radio waiting for forum replies, try to confirm all of the things in the radio that DO work. does the squelch operate normally?
does the radio receive actual signals or just static? etc...
you can also use that voltage chart to start going through the radio comparing voltages on the audio amp, and any other transistor you decide is worth testing.
this is to help keep you moving and sometimes doing these things can help you stumble on your culprit, even if by accident.
do you have an external SWR meter?
if so, put it in line between the radio and the antenna/dummy load and set it to the CAL (calibrate) position. now turn the knob on the meter all the way to the left and key the mic.
while TXing, turn the knob until the needle sits about center of the meter.
now start yelling and caterwauling into the mic (dynamike all the way up of course) while watching the needle.
did it waver at all? any movement is a good sign.
post back after you mess with it a bit and try to give us a detailed description of what you encountered. the more detailed you are, the better responses you will get.
i am hopeful that something you notice will perk an ear of one of the gurus here who might be able to lend a hand.
good luck!
LC
