Williams Fire! (Williams, 1987) hi all help for newboy williams sound prob

[mlovell30uk]

Hi all I'm new here so hope this is OK iv got a Williams fire pinball system 11 the background sounds are fine but sounds that are made on the main board speech are very quiet and break up if you press the sound test button the speech starts of OK then suddenly drops qweat and crackly if you press the button again same thing happens loud then drops off hope this helps the 12- is at 14v thanks for any help