[DMcMahon]

Checked playback of pre-recorded music cassette out to external Hi-Fi amplifier using the Radio-Phono output DIN pins (BU 1 pins 3 & 5) with headphones connected to the amplifier.

Playback sounded good but noticed during the silent breaks between tracks that there was a noticeable hum present (particularly at the higher volume settings) on both channels, the level of which could be changed by use of the volume control on the amplifier. Maybe would not be so noticeable with speakers connected.

Found that the hum was always present in any mode of the tape deck, i.e. play, record, rewind, fast forward, paused play and standby (powered but no keys pressed), but largely masked when music playing.

Rechecked playback with headphones connected to the tape deck headphones socket and basically got identical hum results.

Surprised that the hum is present in the non Play modes (like fast wind etc) as thought the playback amp would be muted.

Looking at the schematic it looks like the Phono line outputs are switched through to the DIN socket by playback switch S 110, so surprising that the hum signal is being output in the non playback modes.

Will need to dig out scope and try and trace the origin of the hum signal, first checking the power supply DC supplies for any mains ripple etc.

David