ZX Spectrum IC25

The IC25 is a 74LS157 Logic IC and can be replaced with a modern 74HCT157 Logic IC

A modern replacement can be found here:


Using a multimeter check the traces for IC25, the the diagram below for chip pin position

PinTraces toVoltage
1IC26 Pin 1
2IC3 Pin 2
3IC3 Pin 3
4Upper Ram (IC15-22) Pin 10
5IC3 Pin 5
6IC3 Pin 6
7Upper Ram (IC15-22) Pin 11
8IC24 Pin 7
9Upper Ram (IC15-22) Pin 12
10IC3 Pin 10 / IC2 Pin 33
11IC3 Pin 11 / IC2 Pin 40
12Upper Ram (IC15-22) Pin 13
13IC3 Pin 13
14IC3 Pin 14
15IC3 Pin 15
16IC3 Pin 16