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4-4 Status Display Board Diagnosis
Using the Status Display Board for Failure Analysis
Although the four digits displayed on the LEDs can narrow the problem down to a small
area, there is much more information available. It can be read by the controller using the
disc memory command set. It is also available at connector J2 (see Figure 4-1). The module
is designed to fit on this connector and present this information as an LED display. To use
the module, follow this procedure:
1. With the power turned off, remove all interconnecting cables from the 9895A.
2. Pull the front cover off.
3. Locate connector J2 (Figure 4-1). Slide the module onto this connector, component
side up.
4. Hook the +SV clip onto the +SV pin.
If
the +SV pin is missing, +SV is available at the
top of the LED display.
5. Turn power on. The start-up sequence includes the basic self-test.
6. After the self-test has finished running (that is, the LED pattern has stopped chang-
ing), press and release the self-test switch.
7. The basic self-test should now occur. When it has finished running, put an initialized
scratch disc in each drive and close the doors.
8. Pressing and releasing the read/write enable switch and hold it in until after pressing
the self-test switch. The basic self-test with read/write should now occur.
9. To make self-test repeat, short the loop pins together.
Self-test information can be read directly from the LED's, using the methods presented in
the next section.
Obtaining Test Results From LED Display
The two pieces of information which we are interested in are the four-bit test number and
the five-bit subtest number. The test number appears as four red LED's labeled TEST. The
MSB is toward the 9895A. The subtest number appears as five green LED's labeled SUB-
TEST. These two numbers are listed in Table 4-2, along with the meaning of the code. Note
that only nine of ten error code bits are used. The tenth digit is always zero, as can be seen
by using the controller and command set, which present all ten bits.
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