Have one confirmed display from a 6 digit set and another from a 7 digit set that is giving me some flicker and segment issues.

Tested the 2N7000 segment drive transistor and seems like it is the culprit but may also be the decoder because of the flickering.

Had tested on the bench top with a 5 volt power supply per the directions to give a number “8” in each digit.

Can I modify the wiring to the display to get other numbers 1-9 by changing which pin has ground or voltage on pins 16-19 of the BCD D0 thru D3?

I made a wire harness when I built these per the table below. Thx

DF9A4C6C-841D-4A76-9D7F-1C83D180A967 (resized).png

I looked up the display schematic and decoder chip truth table for connection to pins# 16, 17, 18, 19 as follows:

0 = 0000 (all grounded)
1 = 0001 (only pin 19 at 5 volts, others grounded)...
2 = 0010
3 = 0011
4 = 0100
5 = 0101
6 = 0110
7 = 0111
8 = 1000
9 = 1001

May be back asking how to fix a burned up display but it was fun trying to figure it out.

Verdict- mixed

Bench testing of one of the displays helped identify and then confirm that replacement of one of the segment drivers was successful.

The other display was capable of displaying all the digits clearly during benchtop testing but not in the machine. It required a new U1 to repair it.

Overall it was a good exercise to understand how the BCD binary data stuff creates the different numbers.