Epson MX-80 Technical Manual page 58

(2) Trouble with 8041
It is difficult to thoroughly troubleshoot the 8041 with the IC mounted on the control cir-
cuit board. As one of the methods to troubleshoot the 8049, it is possible to determine
whether or not the internal elements of the 8041 are operating, by checking the following
signal from the 8041 for normal output.
(a) Signal SYNC at Pin No.11
SYNC
~
I
L
If-'~-----
2.5
/ J . S - - - - - - - - i · 1
Fig. 3.19 Normal Waveform of Signal SYNC
If signal SYNC is not properly output, replace the 8041 with a new one.
(3) Trouble with 8155
The LSI 8155 is connected with the main CPU 8049 and the slave CPU 8041 on the
same bus. Therefore, some difficulties may be encountered with in distinguishing
troubles peculiar to the LSI 8155 from those peculiar to other LSI's. Since the 8155 con-
trols data transfer between the Printer and an external device, one way to indentify the
trouble with the 8155 is to check the I/O ports of the LSI for proper input/output of exter-
nal signals.
Table 3.6
I/O ports
I
Direction Voltage at port
PAO to PA7 (Pin Nos 21 to 28) In Approx 5V (when the Printer
IS
not
connected to an external deVice)
PBO to PB7 (Pin Nos 29 to 36) In Approx 5V (when the print head is not
driven)
PC 1 (Pin No. 38) Out (BUSY)
Approx 5V (when the Printer
IS
busy)
PC2 (Pin No 39) In (ST8)
Approx. 5V (when the Printer is not
reading data)
PC3 (Pin No.
n
Out (SLCT) Approx 5V (when the Printer is not
In
the selected state)
PC4 (Pin NO. 2)
Out Approx. 5V (when the print head
IS
not
driven)
- -
NOTES 1. "Direction" refers to the flow of signal as viewed from the LSI 8155.
2. Be sure to remove the option board before performing the above check.
When any of the voltages measured at the respective ports is abnormal under the condi-
tion described in parentheses, the LSI 8155
IS
considered defective due to the I/O port
failure. Replace the defective LSI with a new one.
3-21
REV. A