Voice stops and sound bar changes from colour to black but tape is still recording Philips Pocket Memo DPM 8000

[Piper Craig Lawyers]

We have had several issues when transcribing from someone using the Philips Pocket Memo DPM 8000 - the sound is there and the colour is on the sound bar showing the voice and then it's like the person recording it hits something on the dictaphone and the time is still recording but the sound bar goes black and there is no voice coming through.  It's  like the person dictating is hitting a "mute" button or something but still recording as the timer is still going.  Can't find anything in the manual to assist.  Please help!!