Troubleshooting Of Control Circuit Board; Fig. 3.17 Normal Waveform Of Signal Psen - Epson MX-80 Technical Manual

3.4.3 Troubleshooting of control circuit board
When troubleshooting the control circuit board, it is unnecessary to look into each compo-
nent on the control circuit board. The electric circuit components that can be replaced by the
user are limited to those shown in Table 3.3. Therefore, other circuit elements must be left
intact unless the user has received special training on the handling of electric circuitry.
In this paragraph, a process of finding out which one of the components on the control circuit
board should be replaced is described if any trouble with the MX-80 is attributable to the
control circuit board. As previously mentioned in paragraph 3.4.1, troubleshooting of the con-
trol circuit board can be completed by replacing one of the following major components
shown in Table 3.5. In this case, the driver circuit board must be removed to observe signals
from main IC's 8041, 8155, etc., since the control circuit board is located beneath the driver
circuit board.
Table 3.5 Major Components on Control Circuit Board
Name of component
Part number
8049
(CPU) Al01680492
8155 (RAM
and 1/0) Al01681551
8041
(slave CPU)
Al01680412
Control cirCUit board
G490201001
(Including
8049. 8155
and
8041)
~
As a result of troubleshooting the contorl circuit board by the methods described below, if no
defective circuit element can be discovered, replace the entire control circuit board includ-
ing all IC's, with a new one to solve the trouble with the control ci rcuit board.
NOTE: Circuit elements such as 8049, 8155, etc. are extremely complicated in construc-
tion, and trouble with those elements may not necessarily be detectable by the
methods described below. To perform sufficient check, consultation of the data
sheet of each LSI is recommended.
(1) Trouble with 8049
Trouble with the 8049 can be discovered by checking the following two output Signals
from the 8049. If either signal is not properly output, replace the 8049 with a new one.
(a) Signal PSEN at Pin NO.9
PSEN
-,L,.. __ ----.l 1
!
I
r--
! .
Approx. 5V ... _ _ _
....J
1
I-I·~~--
25
f. . / , S
· 1
Fig. 3.17 Normal Waveform of Signal PSEN
(b) Signal ALE at Pin No.11
ALE~
I
1-1-------2.5
f../,S------~-I
L
Fig, 3.18 Normal Waveform of Signal ALE
REV. A
3-20