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Maintenance
Table 4-1.
Meanings of Self-test LED Indicator Patterns
LED
PATTERN
BEING DISPLAYED
TEST FAILURE SIGNIFIED
BY LED PATTERN
7
6
5
4
3
2
l
0
(WHICH TEST FAILED)
*
*
None
*
*
*
Basic Instruction Set Test
*
*
*
ROM Test
*
*
*
SDLC Test
*
*
*
*
SDLC Test with OMA
*
*
*
BI SYNC Test
*
*
*
*
BI SYNC Test with OMA
0
0
0
0
*
*
*
RAM
Test
*
*
*
*
RAM Test Parity Error
*
*
*
*
Timer Interrupt Test
*
*
*
*
*
BISYNC and SDLC Tests w/DMA
Legend:
*
=
LED lighted
0 =
When lighted, the coded pattern signifies which
chip (bit) has failed
(see table 4-2)
g.
Replace the RAM chip that was
identified
in
table
4-2
as
being
defective.
(See paragraph 4-17, "Field Replacement of
a RAM Chip".)
h.
Repeat steps d through g (to cover the possibility that
more
than one RAM chip had failed simultaneously).
i.
If the LED 7-6-1-0 combination is lighted, one of the parity-
bit RAM chips has failed.
Replace both parity-bit RAM
chips
(U97 and U98).
(See paragraph 4-17,
"Field
Replacement
of
a RAM Chip". )
4-8
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Troubleshooting
