Radio Shack TRS-80 - Page 168

Possible
Solution
In
either of
the above
cases,
shut the
Computer off
completely. (Or, as they
say
in the
big
time, "Take
it
all the way
down.")
Let it
sit
for a full
minute
before turning
it
on
again.
Turn the
machine
back on, type
NEW and try
the
P.M. test
again. If the results
are the
same, there
is
probably
a RAM or
ROM
failure
that
will
require Radio
Shack
Factory
Authorized
servicing.
B.
One Last Try
Before
full
panic sets in,
however, type
NEW
and enter
this program. It assigns
every
free
memory
location
in RAM a
specific value,
then
reads that
value back out
onto
the
screen.
Type (very
carefully):
10F.X=lTO876:A<X)=X!N.X:F.Y=lTO876:P.A(Y)s
20IFA<Y )-A(
Y-n<>lP.
"BAD"
30N . Y
Then,
initialize A(0) to
zero by typing
A(0 }
=
Then,
RUN
After
about
a
10-second
wait
for
the array
to "spin-up",
the
monitor
should
display
12
3
4 5 6 7 8
(etc
.
,
through
8 7
6)
If the
word
"BAD"
appears
on
the screen,
you may
have found the
problem.
You
will
probably
want to
enter
this test
program into
your
computer,
try it out
before
you
need it, then
save
it on
tape
and hope
that you
won't
. .
.
(need
it,
that is).
Video
Display
Problems?
The Video
Display
is very
similar to a
television set.
It has
adjustments
for
brightness, con-
trast, horizontal and
vertical
sync,
etc. If
these
fail to
give the
desired display,
the
problem
could
be in the
Computer.
Horizontal
and
vertical
centering
and
"jitter"
can be
controlled
by simple
internal computer
166
>
\wf.
program
in memory,
bat
at
i piobmj?
Mat anyway-
Vim
could
try
to
save
it
oit
cassette
.tape
before
taming
«!(.
the
machine it
it
matee#yoirfeel
any
better,
.
ROM.
—
that's
Read- flinty
Memory.
tor
8K
of memory
T
use
1889
instead of 876
irti
Line
1(9;
for 16K,
use 3947.
or 1889
-..or
3947.
M