So out of the 8 Pentas I have been working on 7 are serviceable with just 1 needing the caps replacing (as a routine but working fine).  The sticky one has what I believe to have been a self induced problem.  I inadvertently left the earth lead off board 22 when I reassembled it and although the speaker worked for a while it crackled and stopped fairly soon.

I assume that the earth lead has shorted on the back of board 1, which is in the area of mainly solid state resisters etc which I will check.  It is also in the area IC1 board 1 a HEF4066BP switch chip.

My question is when looking for a replacement and comparing the three lines of numbers on the existing chip, there are loads with the number HEF4066BP but they all have different numbers on the second and third lines.  So can I disregard the numbers on the second and third lines and simply order one with a matching HEF4066BP on the first line?

Cheers

Nick