Re: uBitx just started transmitting a loud hum #ubitx-help


 

An audio recording of the hum will be nice.

Raj

At 09-04-18, you wrote:
Thanks for the great replies,

I haven't been through all of the grounds exhaustively, but all jacks/pots/rotary encoders and switches I have soldered are properly grounded to the ubitx main board (0 ohms on multimeter). I have also confirmed the emitter of q6 is grounded via r63 and r64. Emitter of q70 is grounded directly.
The main board isn't earthed (it's inside a plastic chassis) and is only grounded via power supply -ve terminal.
Haven't had a chance to try it with a 12v battery, but will do in the next day or 2. No RF earth at present.

Q70 is showing 0 volts on Tx, but there is a visible fine wave form on the oscilloscope when probing during tx. I haven't got a capture of it to measure frequency but I suspect this is related to the noise I am hearing.

Will continue to work through the suggestions re audio circuit tests and report back.

Also, yes it was a WX branded TDA2822 that failed.

Cheers,
James

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