Quantar TTN4094 SCM NO Modulation Repair

U306If your repeater keys up without modulation or very low modulation, either in P25 or analog, it might be because U306 on your SCM is dead. This seems to be a common fault on the TTN4094 board, I have heard about this issue from a lot of P25 enthusiasts and had this issue more then once myself. U306 are MAX292EWE a 8th-order lowpass switched capacitor filter, they are part of the audio processing, you can find the data sheet here. To verify that U306 is dead you can scope the input pin 14 where you should see a signal then scope output pin 11, if there is no signal or a signal which is orders of magnitude smaller then the input, replace U306.


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