Sharp MZ-80B - Page 10

The CPU b~ard is composed of the following six blocks. When it malfunctions, first locate which block is concerned
with the
malfunctions, and next try to check for its corresponding circuits; the wiring diagrams of every block will
be shown separately.
CPU inoperative
Display
block
Cassette
recorder
block
Keyboard
block
Audio
block
NO
Clock block
NO
YES
YES
YES
YES
YES
<e
noperative YES
immediately after >------0-1
power ON,
NO
Check RAM and its
peripheral circuits {by
usinfj RAM checked,
Check video
RAM circuit.
Check IC23
(8255) and its
peripheral parts,
Check
IC24
(LH0081A) and its
peripheral parts.
Check
IC23
(8255) and its
peripheral P<lrts.
----'
Check IC19
(8253) and its
peripheral parts,
Check
memory circuit
and its peripheral parts,
• Checki~g rnetl1ods()f~~h circuit
-,,;
"I, "," .. ,,,' "_ • ",. '" _
:.l.C.By .tbuChinglC package by fingers:c .
.•. Ifthey seem too hot by heat gene~atiori;
2.
I(:::--j{ defective" le 'Idad 'is 'hea~'y 'or ~'~mporients are ~ouc~~- '"each' other (ROM and V·RAM are
. ex.~mpted f;~m this checking).
e, If.- a circuitry state changes to, an~ther; Sold~ring is- poor, socket contact is impro'per or printed-
wiring is erroneous.
By using a synchroscope:
• If the relation between input and output of TTL IC is illogical, this means defe.etive IC gate.
•
Check if the voltage of TTL IC is as specified: Highle,;el; over 2.4V"Low level; below O .. 5V.
• When the signal'is between the high and low levels, is ~here circuit t?uching or !C malfunction?
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