Epson PX-8 - Notes on Repairing;Replacing the MAPLE Board

REV.-A
6.5 Notes On Repairing/Replacing The MAPLE Board
Care must be used on the following points when repairing or replacing the MAPLE board.
6.5.1
Voltage/Current Checks
Non-reproducible program runaways or data changes which cannot be attributed either to sof-
tware (including the programming) or hardware may occasionally occry. Battery charging prob-
lems which are difficult to reproduce may also occasionally occur. In such instances, check the
following voltages and the charging current before repairing the board.
1)
Setting-up test equipment
Connect a DC voltage regulator in place of the main battery, a voltmeter, and an ampere meter
as shown in Fig. 6-11 .
DC voltage
regulator
Computer
}
CN 1 battery connector
or ac adaptor connector
VB+~t-----r
GNDE-t--~
* If an ampere meter is incorporated
in the DC voltage regulator, no addi-
tional ampere
meter is required.
Fig.6-11 Setting-Up a Voltage and Current Measurement Device for Testing
the MAPLE Board
If the DC voltage regulator has a current limiting feature, adjust it so that it works above 500
mA. Adjust the voltage output to +5.0V and make sure that the computer is off before applying
the regulator output to the computer. If a higher voltage is inadvertently applied, circuit com-
ponents may be damaged .
• Press
the INITIAL RESET switch once and then set the computer POWER switch ON.
2) Voltages
(Low voltage detection level)
Lower the regulator output voltage while observing the VB+ voltage on the MAPLE board. Mea-
sure
the voltage at the time the message, "CHARGE BATTERY", is diplayed on the LCD panel.
The measured
voltage should be in the following range:
4.61 V
~ 4.82V
Note) When the message appears, the VB+ voltage rises a little higher than the value mea-
sured
immediately before; this occurs because the BV+ line is backed up by the auxi-
liary battery.
(A.,.D converter voltage)
Adjust the VB+ voltage to 5.0V and then make sure that the voltage across the test terminals
VRF is 2.0V.
3) The VB+ line current varies depending on the line voltage and operation. Table 6.5 lists the
standard current requirement for the various components. The following current measure-
ments may also vary depending operation mode.
6-8