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5.5.3 Power Supply
Checks
If a problem exists in the Model 706, the power supply should
be checked initially. The power
supply
checks are listed in
Table 55. Use the DMM recommended in Table 5-4 to check
the
various test points. It is also a good idea to check each
supply level with an oscilloscope to be sure there is little or no
noise or ripple.
NOTE
The thermal breaker (TB-3) that is in series with the
. _
AC line and the power supply opens the circuit
when
the
temperature
inside
the
instrument
reaches 65%. This action shuts off the power to the
instrument.
In this case turn the Model 706 off and
Step
1
2
3
4
5
Item/Component
6
7
U105 pin 8
U105 pin 2
U105 pin 6
U105 pin 40
U105 pin 37
U120 pin 21
8
U120 pins 2-9
let it cool down for approximately
one hour. Then
turn the power back on. The thermal
breaker
should
return to normal operation
(which means
the circuit is closed).
5.5.4 Digital
Circuitry
Checks
Problems with the digital circuitry could cause erratic opera-
tion. Check the various components
associated with the
digital circuitry, including the IEEE interface, using the infor-
mation in Table 5-6.
5.5.5 Display Board Checks
Check the display board per Table 5-7.
Table 5-6. Digital
Circuitry
Checks
Required Condition
Power On
+5v f5%
(4.75V to
5.25V)
+4V *20%
13.2V to 4.8V)
+4V &20% (3.2V to 4.8V)
Turn
Model 706 off then
on.
1 MHz Squarewave
100pec negative going
pulses, variable intervals.
0 to +4V, 2ms Pulses
Table 5-7. Display
Board Checks
Remarks
Voltages referenced to
digital
common.
+ 5V digital supply.
MPU Hm
line.
MPU NMI line.
RESET line pin 40 remains LO
for about 1 second after
power
on then goes HI.
Also check for system clock on
U103, U120, U102 and U118
pin 11.
iR0 line.
Display and NVRAM data.
Step
Item/Component
1
Activate front panel
PROGRAM 8.
2
J/P1010 pins 9 and
14
3
U203 pin 1
4
U203 oin 8
Required
Condition
Remarks
+5v f 5% (4.75V to
5.25V)
Check to see that all LEDs
are functional.
Check that all
annunciators are functional.
If LO, check per
Table 55.
Update Data
Clock
5-7
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