Posted By
andysquiz
on 2021-12-20
09:14:57
|  Re: Cartridge port Not working correctly
Morning all,
I have got voltage readings from U20,21 and 22 as requested. I have done the checks with the cartridge fitted and with it removed
U20 74LS139
PIN Volts PIN Volts
1 4.55 16 4.82
2 0.16 15 1.9 No change in voltage cartridge was fitted or removed.
3 0.16 14 0.7
4 5.55 13 0.7
5 5.6 12 1.24
6 5.6 11 5.6
7 5.6 10 5.6
8 EARTH 9 5.6
U21 74LS125
PIN Volts Cart fitted PIN Volts Cart fitted
1 4.8 4.76 16 4.8 4.8
2 0.25 0.15 15 4.24 1.5
3 4.2 4.24 14 0.16 4.2
4 1.8 1.167 13 3 1.6
5 1.2 1.55 12 3 1.3
6 4.28 4.25 11 0.155 4.25
7 0.163 0.162 10 4.2 1.62
8 EARTH EARTH 9 0 1.05
U22 74LS27
PIN Volts Cart fitted PIN Volts Cart fitted
1 4.83 4.76 14 4.83 4.81
2 5.8 2.56 13 EARTH EARTH
3 1.6 4.13 12 0.66 0.104
4 0 1.73 11 0.09 1.74
5 EARTH EARTH 10 EARTH EARTH
6 4.42 0.7 9 0.16 4.24
7 EARTH EARTH 8 4.45 0.72
U20 doesn't change with a cartrdige fitted
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