IBX100 sound components - revision A

[Ralph Barrett]

In response to Marl Leman's enquiry, I've spent some more time mapping
out the IBX100 sound circuit, and comparing artwork to my ESP RiscPC
16-bit sound card.

Warning - there are bound to be some mistakes in the following. Use with
care. This is Revision A of this list and is incomplete. No doubt a
correct definitive list will be posted in the future (do a search - do
not rely on this list).

I still believe that IC2 is a TDA1545A DAC. IC2 and IC3 share the same
filtered power feed that appears dedicated to the analogue sound
circuitry. IC1 uses the digital +5v. This implies that IC2 is the DAC
and IC3 is the op amp. I reckon IC1 is a flip flop (J-K type) ??

On IC1 :-

pin 6 (out) is BCK to IC2 pin 1
pin 3 (out) is DATA to IC2 pin 3
pin 9 (in) is SDCLK from ARM7500
pin (in) 10, 12 is reset 
pin 13 (in) is SDO from ARM7500

So all we've got to do is find a 74ACT series TTL using these pins in a
sensible manner (or perhaps take the lid of my RiscPC and have a look!).

I've checked through the artwork and I am now pretty sure that IC2 is
the philips DAC. Remember that some of these ICs are the wrong way
around. Also that IC2 and IC3 do not use the normal digital +5volt
(VDD?).

Here is my first take of a suggested components list :-

IC1 74ACT78 ?? or 74ACT108 ?? (confirmation to follow)
IC2 TDA1545A or equivilent
IC3 TAA1308 or equivilent

L1 inductor filter for analogue sound supply +5v
C12 10uF capacitor filter for analogue sound supply +5v
C2 100nF *   *= recommended components from TDA1545A data sheet)
R8 22k *
C10 1uF *
R7 33k *
C5, C3 1uF +  += from ESP board
R2, R1 3.9k +
C6, C13 100uF 16v +
R3, R(not marked?) 10k +
R6, R(not marked) ?? (these are not fitted on my ESP board)
X2 11.2896Mhz +
R20 ?? series resistor for xtal oscillator

C9 appears to be in parallel to L1 ???
C14 does not appear to be part of the sound circuit ?

Er that's it for now. Comments welcome.

Ralph