CL CLOCK CHECK: Connect scope to
U3C
, Pin
4.
Output should
be
similar
to
WAVEFORM
14.
END
BLANK CHECK: Connect scope
to
U3C
, Pin 7. Output should be similar
to
WAVEFORM
17
.
VIDEO ADDRESS DECODING CHECK: Check
outputs
of
U5C,
U5G,
and
U5E
.
See
schematic for
scope connections. Outputs should be
similar
to
WAVEFORMS
7,
8,9, 17,22,
23
,
24
,
25
,
28
,
29
,and
30
.
Check outputs of
U5J
and U5K.
See
schematic for scope connections. Outputs should be similar to
WAVEFORMS
23
,
24
,
25
,
28
,
29
,and
30
.Timing and phase relationship
of
U5K and
U51
can
be
confirm-
ed
by
use ofadual trace scope.Set scope horizontal time base to 2mSec.
See
Figure 2for scope connec-
tions and relationship
of
waveforms. This confirms operation of U5K,
U51
, and associated circuitry.
USK
,
Pin
12
U5K
,
Pin
4
US
I,
Pin
4
US!,
Pin
7
US!,
Pin
9
USI
, Pin
12
Figure
2
SYNC
PULSE
GENERATION
-
540
BOARD
For horizontal sync, connect scope to Pin
12
of
U4B.
Output should
be
similar to WAVEFORM
26
and
the negative pulse should
be
approximately
4.7!-,Sec
wide.
For vertical sync connect scope
to
Pin
12
of
U4A. Output should
be
similar
to
WAVEFORM
27
and the
negative pulse should be approximately
300!-,Sec
wide.
~
VIDEO
MEMORY
AND
VIDEO
DEVELOPMENT
-
540
BOARD
The four memory chips
U2C,
U2D
,
U2E
, and
U2F
are the B & W memory.
U2C
and
U2F
comprise
memory for the top half of the moni
tor
display, while
U2D
and
U2E
comprise memory for the bottom
half of the monitor. The video information is fed thru
U3F
to
ROM
(U3E)
to generate the dot pattern to
be
displayed.
U3D
then shifts this information serially
to
the Video Monitor
(J21)
.See Figure 3 to com-
pare timing of memory switch signal to video signal. Set horizontal time base on scope
to
2mSec. This
confirms operation
of
U2C,
U2D
,
U2E,
U2F,
U3D,
part of
U3E,
U3F,
and
aSSOCiated
circuitry.
U2C
,
Pin
8
Vi
deo
Jack
U2D
,
Pin
8
Figure
3
•
COLOR
SIGNALS
-
540
BOARD
To check
X2
crystal oscillator
(3
.579545MHz),connect scope to U2A Pin
8.
Output should
be
similar to
WAVEFORM
11
. This confirms operation of part of
U2A,
X2,
and associated circuitry.
6
•
