[TenTec] Omni V audio distortion

[MadScientist]

I would suggest that the TDA1015 has failed. This would be the same as if one of the transistors in ay complimentary symmetry audio stage went open.

Youcan test this by checking voltage on pin 2 of U10. It should be roughly half the voltage at pins 3 and 5. Pin 7 should also be about half that of 3 and 5.

Also, look at the audio waveform at pin 7 and 6. They should be about the same in appearance . The signal path between pin 7 and 6 is only the tone control so amplitude and shape of the waveform should be about the same at both pins.

You can also eliminate a lot of things by looking at the waveform of the sidetone (carrier level set to zero) when keying in CW. This signal should pass through U10 unchanged in appearance but altered in amplitude, with symmetrical clipping.

TDA1015’s are commonly available on eBay right now.

Try to purchase from a USA or UK seller to reduce chances of getting an empty.

Gary

> On Jul 9, 2018, at 8:44 AM, Martin Sole <hs0zed at gmail.com> wrote:
> 
> Hi,
> 
> I'm sure I read something similar to this recently but I can't locate it now. I think the discussion centered on failing capacitors on the audio board. Anyway my problem here is that I have started to hear quite high levels of distortion on the received audio of my Omni V. Looking with a scope and using a nice big wire wound 10 resistor as a load on the external speaker output with scope across it I see clipping of the negative peaks once they reach about 2.5v peak. Positive peaks can go much much higher before clipping, around 7v. I would expect to see a bit more symmetry.
> 
> The fixed level of audio out is clean so I think everything prior to C37 should be okay. From there the audio circuit is simple, if not crude, a TDA1015 with a simple tone control between sections.
> 
> So, a leaky capacitor?
> 
> Cheers
> Martin, HS0ZED
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