REVIEW OF SCREEN WEAVE & SCREEN FLASH ELIMINATORS FOR NASCOM 2 by R.Dowling
SCREEN WEAVE ELIMINATOR
WHAT YOU GET : A small fibre glass board approx. 1.5 xl inch comes
ready built comprising of one i.c-(74LS90), one socket and one 16 pin plug to
attach to the Nascom as a piggy-back board.
FITTING : Full instructions are supplied and the unit was found to be
simplicity itself in fitting. One i.c. is removed from the main board and
housed in the empty socket provided on the small board which is then plugged
into the consequent empty socket on the main board. One other connection has
to be made to the main board from a terminal pin on the piggy-back board.
UNIT IN USE : On power up it was found that screen weave had
disappeared totally and the resultant monitor display was very pleasing. On
disconnecting the wire link to the main board, the display was exactly how it
was before fitting the unit. However it was discovered at a later date that
the unit is not compatible with the well published modification to recover the
"lost" bottom two lines of graphics characters which is necessary if fitting a
programable graphics generator. The result was screen weave at twice the
intensity originally experienced. As the graphics mod. also has the benefit of
stabilising the screen as a whole, removal of the screen weave eliminator
produced a stable display with only very slight weave noticible if looking
closely at the screen.
CONCLUSIONS : A well documented and finished product but almost the
same effect can be realised by the above mentioned graphics mod., assuming you
don’t mind several wire links running along the top of your main board.
SCREEN FLASH ELIMINATOR
WHAT YOU GET : A fully built fibre glass PCB approx 2.5x2 inches
consisting of two IC’s (socketed), an empty socket, a 14 pin plug and ae few
FITTING : Instructions supplied with the unit are very easy to follow
and consist of removing one IC and fitting this onto the empty socket of the
PCB and plugging the PCB into the subsequent empty socket on the motherboard.
Two other connections are made from two terminal pins on the PCB to plated
through holes near IC7 and IC67. A third terminal pin on the small board
enables the user to switch the unit on and off via a switch or port. Most
– users will not require this facility and therefore will leave the unit
permanently working. It is then only necessary to remove the Snowplough (IC58)
and put it in the spares draw. The Nascom is then ready to be powered up.
UNIT IN USE : The unit produces wait states but the extra execution
time, even for programs that have extensive screen access, is claimed to be
less than 1%. It was found that on continuous tabulation to the screen T 0000
FFF8 FFF8 (enter) took 202 seconds on my standard Nascom running at 4MHz with
a wait state and with the unit fitted took 203.5 seconds. Tabulating data was
found to give a much improved look and on a space invaders program the usual
black streaks across large graphic areas had completely disappeared. Running
the Nascom at 2Mhz showed that the unit did not work at this speed and,
indeed, because the Snowplough IC had been removed, produced large areas of
white streaks. The manufacturers claim that replacing one of the IC’s on their
board from a 74LS74 to a 74874 would cure all. This has not been tried out.
CONCLUSIONS : The screen flash eliminator does exactly what its name
suggests and very neatly too! For what you get it does seem overpriced but the
results are certainly worth the expense.
Both units are available from Edac Engineering, 257 Orphanage Road, Erdington,
Birmingham or dealers at 8.75 & 14.75 exclusive of VAT respectively.