System Troubleshooting and Diagnostics
5.7 Using Loopback Tests to Isolate Failures
5.7 Using Loopback Tests to Isolate Failures
You can use external loopback tests to isolate problems with the console port,
DSSI adapters (SHAC chips), Ethernet controller (SGEC chip), and many
common Q–bus options.
If one or more of these tests fail, check that the DC power and Pico fuses on
the H3604 are OK. There are four Pico fuses located on the back of the H3604
console module. One fuse (F3) is on the outside, the other three are on the
component side.
If a fuse is bad, replace the fuse—not the H3604.
Table 5–10 lists symptoms associated with faulty fuses. Figure 5–10 shows the
location of the H3604 fuses.
Table 5–10 H3604 Console Module Fuses
Fuse
Part Number
Symptom
F1 (+12 V, 1/2 A)
12–09159–00
ThinWire Ethernet LED on H3604 is not lit.
Ethernet external loopback test 5F fails if the
Ethernet connector switch is set to ThinWire.
F2 (-12 V, 1/16 A)
90–09122–00
No console display
F3 (+5 V, 2 A)
12–10929–06
LEDs on both DSSI terminators (Bus 1) on the
H3604 console module are not lit; the DSSI
terminator for Bus 0 is lit.
SHOW DSSI or SHOW DEVICE commands
show DSSI bus 0, but console displays message
indicating that DSSI bus 1 terminators are
missing or not functioning.
DSSI SHAC (Bus 1) test 5C fails (countdown
number 11).
F4 (+12 V, 1.5 A)
12–10929–08
The LED on the loopback connector (12-22196-
02) for standard Ethernet is not lit.
External loopback test 5F for the standard
Ethernet passes, however.
System Troubleshooting and Diagnostics 5–71
