Service manual

MZ-80K
Display Block
~
Character
" Video signal
generator
M
Shift
register
"-
7 H-BLANK
DO
<~/~
"-
7 V-BLANK
-
~ Sync signal
Bus
driver
L--
L--
-
I
D7
--
-'-
~
WR-
Video
RAM
RD
CSD
L--
1r
Display
I-----
Oscillator
~
V
controller
circuit
Address
-/
selector
~
AO
~
A9
I
Block Diagram of Parts around Video RAM
,
Problem
C .... P_
,
,
,
1.
Sync. signal is not
Vertical sync. signal: Check for IC15 and
IC16.
produced.
Horizontal sync. signal: ~ck for IC1O.
2.
Video signal is not
Is V-GATE signal present at pinQ)of IC24?
produced.
Yes;
IC24
No; IC5
Is V-BLANK signal present at pin@of IC24?
Yes; IC24
No; IC20
Is H-BLANK signal present at pin @ of ICll?
Yes; IC17, IC3
No; IC15
Is output signal present at pin '21 of ICll?
~
Yes; IC17, IC3
No; IC29
3.
Displayed character{s) Check for IC29 and CG.
is partly invisible.
4. The display is positionally
Check for sync. signal circuit.
deviated.
-6-