Re: IIGS rom3/rom1 board differences

[dempson@actrix.gen.nz (David Empson)]

Jon <joncco@gmail.com> wrote:

> Hi,
> I just got a IIGS (rom3) and the speaker was broken.  Following an
> entry in the FAQ i checked out the headphone jack, but the leaf switch
> was working just fine.  Plugging in a set of earphones gave sound on
> the left ear but not on the right.  After doing some testing and
> looking at the circuit diagram from the IIGS technical reference
> manual,  I concluded that 1) the path linking both the "L" and "R" for
> the earphone jack is disconnected.  2) the path linking the speaker to
> the earphone jack is broken somewhere.  By following where the
> schematics say they should be connected, I was able to restore the
> sound.  Is there something different about rom3 and rom1 machines
> (which I assumed was what was described in the schematics)?

The first edition of the "Apple IIgs Hardware Reference" manual
(hardback, if I remember right) only covers the original logic board
(ROM 00/01, with 256 KB of RAM). There was a revised edition (paperback)
which includes circuit diagrams for both the original and updated logic
board (ROM 3, with 1 MB plus 128 KB of RAM). They are on large fold-out
sheets at the back.

My copy of the 2nd edition is deeply buried in the basement so I don't
have convenient access to it, but if anyone else has a copy handy they
should be able to look up the details for the sound circuitry.

-- 
David Empson
dempson@actrix.gen.nz