Troubleshooting
TDS 520A, 524A, 540A, & 544A Service Manual
6Ć73
This procedure helps you
determine if the A11 DRAM
Processor/Display or the A12
Front Panel module is bad.
Perform the Low
Voltage Power Supply
troubleshooting
procedure.
Probe J26 and J27 but DO NOT
REMOVE the cables from the
connector (see Figure 6Ć40). The
voltages will change if the A11
DRAM Processor/Display module
is not connected to the power
supply. Probe J26 pins 7, 11, 17,
and 35, and J27 pin 17.
Yes
No
Done.
Yes
No
No
Yes
Power off and remove
the cable from J2 on the
A11 DRAM
Processor/Display
module. Probe P2
pins 10 and 8 with an
ohm meter.
Is
the cable
from the A11 DRAM
Processor/Display module
to the A12 Front Panel
module securely
connected?
Connect the cable and then
perform the Primary
troubleshooting procedure.
Is the
ON/STBY
button working
correctly?
Power off the oscilloscope,
remove the cable from J2 of the
A11 DRAM Processor/Display
module (see Figure 6Ć40), and
power back on.
Is
there a
3.125Ä‚MHz
clock on J2
pin 25?
Probe J2
pin 2, 6, 7, 11, 16.
Are these pins -15Ä‚V,
+15Ä‚V, +5Ä‚V, -5Ä‚.1Ä‚V,
and +5.1Ä‚V
respectively?
No
Yes
Are
these pins
-15Ä‚V, +15Ä‚V,
-5.1Ä‚V, +5Ä‚V, and
+5.1Ä‚V
respectively?
No
Yes
On the A11 DRAM
Processor/Display
module probe J26
pins 3 and 5 with
an ohm meter (see
Figure 6Ć40).
Does
the resistance
between these two
pins dramatically
decrease when the
ON/STBY button
is toggled?
No
Yes
Replace the Low
Voltage Power Supply.
There must be a problem with the
communication link between the
A11 DRAM Processor/Display and
the A12 Front Panel. The A12 Front
Panel module has most likely failed.
Replace this module.
Does the
Front Panel
work correctly
now?
No
Yes
Replace the
A12 Front
Panel module.
Replace the A11 DRAM
Processor/Display
module.
Does
the resistance
between these two
pins dramatically decrease
when the ON/STBY
button is
toggled?
No
Yes
Figure 6Ć38:ăProcessor/Front Panel Troubleshooting Procedure
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