| transistors (TR4) tends to blow up in
response to sudden voltage fluctuations.
This results in the loss of the -5 volt and
+12 volt supplies to the RAM and the
appearance of little black squares over
the screen when switched on. The only
solution is to change the transistor (of
course, if the machine is under guarantee,
then send it back to Sinclair Research).
The change in ULA on the Mark 3s
also brought to light another problem,
because some software houses had not
been following the procedures set out in
the Spectrum manual. The keyboard
input port also reads in a value from the
EAR socket and until now this has been
Binary 1. On Mark 3 Spectrums, this
value was not maintained because, to
reduce power consumption, the values
of the pull-up resistors were altered.
The result is that the EAR bit now
floats until the ULA has warmed up,
and no value has been given for it by
Sinclair Research in the manual. Games
and other software which check the
whole byte, and not just the keyboard
bits, can no longer be used and anyone
owning a Mark 3 is strongly advised to
check before handing over the 'greenies'
that any new purchase is not going to
suffer this problem.
It also turned out that Mark 1's design
caused problems with the Interface 1 -
and thus its compatibility with the ZX
Microdrive. A transistor modification
has had to be made inside the interface
to cut down the time taken to switch on
the unit from power-up.
|
SEXING YOUR
S P E C T R U M
|
|
An amusing divertissement for any known collection of true
Spectrumists is to enquire innocently whether someone can
identify a particular ZX model - or ask how A's machine
differs from that of B. It's a guaranteed crowd-puller! Stephen
Adams fancies he can supply the answers and, taking the
Spectrum by the chips, he details the various stages of
development since its April 1982 launch.
|
After three issues of the ZX Spectrum
and countless modifications, many of
you must be wondering just what goes
on inside that little box of tricks - and
just how you're affected by which model
you have. Well, wonder no longer -
here for your delectation is a comprehensive guide to the Spectrum's innards.
Perhaps the most obvious distinguishing factor of the Mark 1 is that it
sported a grey keyboard. The Mark 2s
and 3s both have a blue background to
the keys.
Internally, the issues have been
|
mucked about a bit. But, for details, check
the annotated photos for the complete
picture. Apart from the RAM changes
and the re-positioning of various major
components, Sinclair Research made
their most radical alterations to the
Spectrum when introducing a redesigned
PCB and a new ULA to their final
version.
When Sinclair Research began work
on the issue 3 Spectrum, a low-powered
version of the ULA was employed.
Even so, a problem with the Spectrum
internal power supply is that one of the
|
Click on the thumbnail for the BIG picture. |
SPECTRUM ISSUE 1 (16K)
APRIL 1982
| SPECTRUM ISSUE 2 (48K)
AUGUST 1982
| SPECTRUM ISSUE 3 (48K)
JULY 1983
|