From clay's data east repair guide:
CPU board Problems Causing Missing or Locked on Segments.
The CPU board can be a problem where a segment is missing or locked on. The CPU PIA at 9B (and to a lesser extent 7B) controls the segments and can fail. Its signals go thru RA21, RA22, RA23 (4.7k resistor networks) and these can also fail.
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I'd start by tracking down which resistor array is controlling that segment and check it with your DMM.