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Cobra 148 nw st sound tracker no RX audio

26TAZZ

26TAZZ

Member
Jul 5, 2012
2
0
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Hi there 73s to all of you guys
I have a 148 nw st radio that wont receive any signal on any modes no green light for RX
But this is where gets so weird radio Transmit on al modes AM-SSB on all channels 4 pin mic from factory PA jack has audio very good audio so is not a audio chip problem no extra channel mods I already check for D21,22 D1,2
TR14,15,16,17,18 and all check good
I'm trying put in a tone but won't even pick any of it any help or tips will be appreciated
 

Just a guess, but if your MB3756 voltage regulator chip has gone bad and is no longer putting out 8 volts on pin 6 in RX it might act like this. I know it was IC4 in some versions of the 148, not sure if it's the same in the Nightwatch radios.

Hopefully one of the smarter site members will weigh in with a more educated opinion soon.
 
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TM86 said:
Just a guess, but if your MB3756 voltage regulator chip has gone bad and is no longer putting out 8 volts on pin 6 in RX it might act like this. I know it was IC4 in some versions of the 148, not sure if it's the same in the Nightwatch radios.

Hopefully one of the smarter site members will weigh in with a more educated opinion soon.
Click to expand...
That radio does not use a MB3756 voltage regulator chip, it's all done with transistors.

You need to test for Receive voltage 8 volts (or so) at the collector of TR44. The Emitter should be a constant 8 to 9 volts. Tr40 is the transmit transistor which apparently is working.

73
 
Dr. Frankenstein said:
That radio does not use a MB3756 voltage regulator chip, it's all done with transistors.

You need to test for Receive voltage 8 volts (or so) at the collector of TR44. The Emitter should be a constant 8 to 9 volts. Tr40 is the transmit transistor which apparently is working.

73
Click to expand...
Thanks for the correction, Doc!
 

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