Sonoma I tried all the buttons but just found something out and it is the problem. I now have to track it down. Pin 5 on the Mic socket has continuity with the chassis. Pin 5 is the TX pin. So Pin 5 is somehow grounded to the chassis.
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0ld style Uniden Grant. Keys when powered up?
- Thread starter Low_Boy
- Start date
there is a good chance your problem lies on the little PC board that mounts on the mic jack.
unmount it from the chassis, and check for continuity.
I'll bet you see a component lead or something sticking up off the board that is contacting the chassis.
that, or C407 is shorted.
LC
unmount it from the chassis, and check for continuity.
I'll bet you see a component lead or something sticking up off the board that is contacting the chassis.
that, or C407 is shorted.
LC
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Well Everything in the mic socket and mic. PC board look good. I almost think the problem may somehow be coming from the Squelch PA potentiometer. Only thing I at one point changed that out. I am running out of ideas.
does the problem happen in PA mode also?
if not, then you know the short is before the line branches off to the PA section.
look at pin 5 in the schematic, and then follow it to the CB/PA switch that is on the squelch pot.
how did you determine that the short was not at the mic jack itself?
LC
if not, then you know the short is before the line branches off to the PA section.
look at pin 5 in the schematic, and then follow it to the CB/PA switch that is on the squelch pot.
how did you determine that the short was not at the mic jack itself?
LC
Not quite sure if that was a determination or a assumption. I could not find a problem in the mic socket or board. I get the same results weather I remove the squelch pot. or the mic. socket. I can not seem to find a problem with either.
Just some findings. There is a red wire that goes from a center lug in the squelch/ pa pot. that goes to pin 5 of the mic socket. Removing that wire does not correct the problem. This problem is the same in PA or CB. moving the squelch back and forth quickly will occasionally take this out of TX for a very small fraction of a second.
Just some findings. There is a red wire that goes from a center lug in the squelch/ pa pot. that goes to pin 5 of the mic socket. Removing that wire does not correct the problem. This problem is the same in PA or CB. moving the squelch back and forth quickly will occasionally take this out of TX for a very small fraction of a second.
ok i just want to clarify something else because it would lead in two different directions.
can you meter from PC board ground (any tuning can) and the chassis of the radio?
do this with both the power on, and the power off on the radio.
I want to know if you have a DC connection from PC board ground to the chassis.
if not, and pin 5 of the mic socket shows shorted to the chassis with both the squelch pot and the mic jack not physically connected to it, we may have different issue.
right now im confused right along with you.
LC
can you meter from PC board ground (any tuning can) and the chassis of the radio?
do this with both the power on, and the power off on the radio.
I want to know if you have a DC connection from PC board ground to the chassis.
if not, and pin 5 of the mic socket shows shorted to the chassis with both the squelch pot and the mic jack not physically connected to it, we may have different issue.
right now im confused right along with you.
LC
Any chance that someone has attempted to install a roger beep in this radio some time in the past?
Or, for that matter has a roger beep been removed?
A solder blob on the mike-socket pc board would do this.
73
Or, for that matter has a roger beep been removed?
A solder blob on the mike-socket pc board would do this.
73
Mic socket PC board looks good.
No continuity between board ground and chassis ground with power on or off.
pin 5 has continuity with board ground not chassis ground.
3 back tabs on squelch/pa have continuity with chassis ground. working radio does not. the white, red and green wires that go to those tabs go to the correct spots in th
e board.these are the 3 solder tabs closest to the front of the radio.
I have to take the pot out of the radio again and look at it possibly it is bent and touching the chassis. Although it has been out many times I probably would have noticed it.
Thanks
No continuity between board ground and chassis ground with power on or off.
pin 5 has continuity with board ground not chassis ground.
3 back tabs on squelch/pa have continuity with chassis ground. working radio does not. the white, red and green wires that go to those tabs go to the correct spots in th
I have to take the pot out of the radio again and look at it possibly it is bent and touching the chassis. Although it has been out many times I probably would have noticed it.
Thanks
well that's a completely different story!
saying that the mic TX pin is shorted to the chassis is completely different from saying that it is shorted to PC board means something very different.
of course it is shorted to PC board ground, because the radio is in TX mode.
put the mic jack and squelch knob back in place, and move your attention back to the MB3756 voltage regulator.
i know you have checked it before, but just for fun, lets do it again.
radio on, no mic connected, radio is in TX mode right?
measure the voltages on pins 1-8 of the MB3756 and post them here.
you should measure 8 volts DC on pin 6 if the radio is in receive mode.
you should measure 8 volts DC on pin 8 if the radio is in transmit mode.
pin 5 is the pin that switches that voltage from pin 6 to pin 8.
my guess is that you will find 8 volts on pin 8, seeing as how the radio is stuck in TX mode.
if that's the case, unsolder pin 6 and pin 8 from the PC board and bend them up so that they are not making contact with the board.
now check the voltages again.
you should see 8 volts on pin 6 and when you key the mic, you should see that voltage move to pin 8.
please post the results of your experiment.
LC
saying that the mic TX pin is shorted to the chassis is completely different from saying that it is shorted to PC board means something very different.
of course it is shorted to PC board ground, because the radio is in TX mode.
put the mic jack and squelch knob back in place, and move your attention back to the MB3756 voltage regulator.
i know you have checked it before, but just for fun, lets do it again.
radio on, no mic connected, radio is in TX mode right?
measure the voltages on pins 1-8 of the MB3756 and post them here.
you should measure 8 volts DC on pin 6 if the radio is in receive mode.
you should measure 8 volts DC on pin 8 if the radio is in transmit mode.
pin 5 is the pin that switches that voltage from pin 6 to pin 8.
my guess is that you will find 8 volts on pin 8, seeing as how the radio is stuck in TX mode.
if that's the case, unsolder pin 6 and pin 8 from the PC board and bend them up so that they are not making contact with the board.
now check the voltages again.
you should see 8 volts on pin 6 and when you key the mic, you should see that voltage move to pin 8.
please post the results of your experiment.
LC
Well before I start unsoldering I have 8.45V on pin 5 and 8.45 on pin 8. Could this be transmitting and receiving at the same time with out the RX/TX light being that pinkish color? The 8 pin reading is.
1 8.49V
2 NC
3 .424V
4 .O42V
5 .190V
6 8.46V
7 13.57V
8 8.45V
Thanks.
Edit for giggles I unsoldered pins 6 and 8. I lost the channel display. The radio is out of TX. And with the mic. Plugged in I now get no TX. and the red TX light is lit. I still have 8V on pin 6 and 8 with mic. keyed or unkeyed.
1 8.49V
2 NC
3 .424V
4 .O42V
5 .190V
6 8.46V
7 13.57V
8 8.45V
Thanks.
Edit for giggles I unsoldered pins 6 and 8. I lost the channel display. The radio is out of TX. And with the mic. Plugged in I now get no TX. and the red TX light is lit. I still have 8V on pin 6 and 8 with mic. keyed or unkeyed.
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The voltage on pin 3 is incorrect, that's the VRef pin. That should read +8V. Replace C133 and C134 and see if that restores operation. Let us know how you get on.
Also, does unsoldering the wire going to pin 5 on the mic jack get it to drop out of TX?
~Cheers~
Also, does unsoldering the wire going to pin 5 on the mic jack get it to drop out of TX?
~Cheers~
Still stuck in TX with the red wire removed from pin 5. Also still in TX with C133 and C134 removed
