Flashwriter II documentation: https://deramp.com/downloads/mfe_arch...
Before I actually replace the 7406 opencollector inverter chip, let me know if you see anything else that I'm overlooking that I should try first.

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0:00 Introduction
1:15 7406 inverter
1:55 Resistance measurements
2:52 Continuity checks
3:33 Scoping signals
7:32 Keyboard connector
7:40 Wrong output!
8:32 Flashing screen test
10:14 "Composite" out & TTL out match
12:28 Misleading manual
13:38 Part selection table
14:01 Schematic analysis