GW Instek GDM-8245 - Digital Circuitry Checks

GDM-8245 Service Manual
42
7
U602’s clock
Pulse train of about
268Hz can be
measured
On J601, pin 12 to pin 16
Digital Circuitry Checks
Digital control related problems can be checked out by
using table 3 listed below. Besides, service personnel can
refer to the digital control logic section in ―Theory of
operation‖ for more information.
Table 3
Step
Item
Expected Conditions
Comments
1
Power-on self test
LED display should be
lit up for 2 seconds
after a short beep.
Push down the power button
to start the test
2
U202, pin 20
Digital common
When checking GDM-8245’s
digital control circuits, all
the digital signals should be
referenced to this digital
common.
3
J202 pin 40 to pin
20
+5VDC
+5V power supply for the
digital control circuitry
4
U202, pin 19
4MHz clock pulse
Micro controller’s 4MHz
clock pulse
5
U202, pin 9
Low on power-up,
followed by a 300ms
High pulse and then
returns low
Micro controller’s RESET line
6
U202, pin 34
Three-micro-second
long positive going
pulses
Latching signal for relay
control bits, shows up when
relay settings is changed
7
U202, pin 36
Three-micro-second
long positive going
pulse trains
Latching signal for
refreshing data bits going to
and coming from the front
panel
8
U202, pin 14
Pulse stream of
around 53Hz
Keep pushing down one of
DCV, ACA, MAX/MIN or ▼
buttons
9
U202, pin 15
Pulse stream of
around 53Hz
Keep pushing down one of
ACV, AC+DC, ▲ or SHIFT
buttons