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Model
8901B
Service
a
CPU External Register (RAM) Check
1. Perform the Power-Up Chechs on Service Sheet BDI.
a C P U 1 / 0
Port Check
1.
If the Digital Test/Extender Llonrd is not already extcriding
A12
or
A13, plug
it i n t o
the empty
slot in the Digital Section.
NOTE
2. Key in 0.2 SPCL. Check the INSTRUMENT BUS test points on the extender- board
wit11 a n
oscilloscope or signature analyzer probe (used
as
n
logic probe) as listed in Table 8D--17. If
faulty, see Service Sheet 24 and check the CPU and li0 port decoders and buffers.
Tuble
80-1 7.
Insfririncwi J l r i r
Ihifu, =Sfup
2
3. Key
in 0.2 S (Shift) 5 S 5 SPCL. Recheck the test points listed i n Table 8D-18. If faulty, see
Service Sheet 24
and
check the CPU and 1 / 0 port decoders
and
buffers.
Table 8 0 - 18. Inslriimcnf
Biis
Ilczia, a S i c p 3
DATA
(H)
0 to
3
TTL
High
4. Key i n the Special Functions listed in Tablc 8D-19.
For
each entry. the indicated
ENABLE
test
point on the estender board shoiild show
low-going
TTL piilses with
; 1
period of approximately
60 nis. All
other ENABLE test points should be T l L highs. If Ihiilty, see Service Sheet 24 and
check the Enable Decoder a n d CPU.
I
SDecial Function
1
Test Point
~
I
0.0
0.1
0.3
0.4
0.5
0.6
0.7
ENABLE 0
ENABLE 1
ENABLE
3
ENABLE 4
ENABLE 5
ENABLE 6
ENABLE 7
8D-58
Service Sheet BD5
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