On Oct 1, 21:31, Tony Duell wrote:
> > I've been thinking about SZ Spectrums all the time.
> > Oh well, I might just ask anyway, since I've opened it up...
> > What is that chip next to the Z80? It's labelled PCF1306P.
>
> If it's another 40 pin chip, then that's the custom ULA chip that
> includes most of the glue logic.
If it's a 28-pin chip it's the ROM, a 23128, IC5. The ULA is the other
40-pin chip, IC1, near the modulator. It may have different numbers
depending on the revision. There's more than one ROM version as well.
> > And why is there a switch glued on top of the Z80 with wires going to
the
> > character ROM? Since it's a localised character ROM piggybacked on top
of=
> > the
> > one soldered to the motherboard, could it be for switching charsets?
>
> Does the Spectrum really have a separate character generator ROM. Doesn't
> sound right to me...
It's not a character generator, it's just code. The screen memory is part
of the main DRAM and accessed directly by the ULA to drive the video. I
imagine the switch is to select different code versions.
The thing I like most about the Spectrum service manual (apart from the
inclusion of a proper schematic and other diagrams) is the fault-finding
list. Most such lists begin with mundane things like checking the fuse.
The Spectrum begins with:
"TV appears dead. Smoke appears" and describes additional symptoms as
"TR4 shorted. TR4 blows again".
--
Pete Peter Turnbull
Network Manager
University of York
Received on Mon Oct 01 2001 - 18:16:57 BST