Hum (interference) in DM-1701

[SO5AJG]

Recently I noticed a problem with the DM-1701 radio, because when I mute the radio completely and it receives the correspondent's signal, there is a humming noise in the background. Of course, you can hear it by putting your ear to the speaker or listening with headphones. Naturally, as the volume increases, the real signal drowns out the interfering one and the problem is no longer bothersome. Does anyone have such a case? The loaded software is OpenGD77. I don't have the original software and I can't check it.

[VK3KYY]

The GD77 has a similar problem when the battery is charged to above 8.4V

[G4EML]

It could also be the backlight dimming. Does it still make a sound if the backlight is set to 100%?

Colin G4EML

[VK3KYY]

Its worth checking the backlight, but from what I can remember , on the handlhelds, we use a PWM frequency well above what people can hear.

Its only the MD9600 which has analogue filtering of the display backlight where we had to use lower frequencies

[SO5AJG]

Charging the battery has no effect on these sound effects, but when the backlight is at 100%, this unwanted sound is almost inaudible. Only when you reduce the backlight does this effect become more audible. So the reason is the display operation.