Editing IBM 5110 Troubleshooting Guide (section)

== Initial Diagnosis Workflow ==

5110 power-on sequence:

# Power LED on rear illuminates.
# PSU rails stabilise (5110 + 5114 if attached).
# Executable ROS self-test runs.
# Language interpreter loads from Language ROS.
# Language banner ("BASIC READY" or "APL READY") appears on the 5-inch CRT.

If any of these does not occur, stop and diagnose at that stage.

=== Stage 1 — No Power ===

* Mains lead, switch, fuse check on the 5110.
* If a 5114 is attached, '''check the 5114 mains lead and switch separately''' — they have independent power.
* Verify PSU rails at the planar power connector.

=== Stage 2 — Power But No Display ===

Same diagnostic surface as the [[IBM 5100]]:

* Front-panel "Display Registers / RAM Hex" switch — confirms video chain.
* Reseat ROS / RWS / PALM cards.
* Check CRT anode HV.

=== Stage 3 — Banner Wrong / Garbled ===

* Language ROS bit error — reseat Language ROS.
* Toggle APL / BASIC — if one banner is clean and the other garbled, isolated to the failed Language ROS.
* On the 5110 the EBCDIC character set is in use — verify that the garble isn't actually correct EBCDIC characters being read as 5100 encoding.

=== Stage 4 — System Won't Read / Write Diskettes (5114) ===

* '''No drive activity at all''' — cable between 5110 and 5114 unseated, or 5114 PSU dead.
* '''Drive spins but won't read''' — head dirty; head alignment; drive belt slipping.
* '''Read OK, write produces unreadable diskettes''' — head alignment, write-protect sensor stuck.
* '''Sporadic CRC errors''' — drive belt aged, oxide shedding from old diskettes, head dirty.

=== Stage 5 — IEEE-488 Bus Not Working ===

* Cable unseated.
* Terminator missing or failed.
* IEEE-488 controller card on 5110 reseat.
* Test with a known-good instrument.