Printronix P4280, Руководство по обслуживанию

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3–22 Troubleshooting
means RAM and ROM for the 68010 are okay, but the 64180 is
not executing instructions. Go to step 7.
d. If the 68010 LED blinks steadily at 1 blink per second, it
means that the 68010 ROMs are bad. Turn off the printer,
remove the CCB (page 5–46), and check that all ROM chips are
inserted in the correct position and with all pins inserted
correctly.
This check will catch out–of–order ROMs and all single and
multiple bit failures of floating–gate EPROMs (the type with the
window, that erase with ultraviolet light).
If a ROM chip was inserted backwards, discard it. Even if it
operates properly, a high current flowed through the
backwards–biased transistors, and its service life is probably
shortened due to thermal damage.
If ROMs appear correctly inserted, they may still be defective.
Sometimes bits “fade” to one when internal floating gates
discharge. This can occur from over–voltage programming,
radiation damage, too many EPROM erasures, etc. Install new
program PROMs (page 5–58).
e. If the 68010 LED blinks steadily 5 times per second, it means
CCB RAM has failed. The most common cause of this failure
during maintenance is turning off the printer too briefly for the
64180 to reset. The 64180 shares memory with the 68010, and
writes to RAM if it is not completely reset. Turn the printer off,
wait at least 15 seconds, then recycle power before accepting this
indication of CCB RAM failure.
The RAM chips are at board coordinates N9 and P9. The sockets
at N8 and P8 are normally empty; this will not cause a RAM
failure. Inspect the RAM chips, sockets and traces for shorts or
missing chips. Damaged traces or sockets call for replacement of
the CCB.
A remote possibility is failure of the 64180 in the start–up
handshake or in the code that programs the memory controller.
Try changing the 64180 RTPU PROM (page 5–58).