ZX Spectrum IC4

The IC4, like the IC3 – 74LS157N – is for the lower 16K of RAM, a bad chip or trace will usually manifest itself as corrupt graphics on the screen

A modern replacement can be found here:

ShopLink
RetroRevivalShophttps://retrorevivalshop.co.uk/index.php?main_page=product_info&products_id=35
Retroleumhttps://www.retroleum.co.uk/zx-spectrum-chips

Using a multimeter check the traces for IC4, the the diagram below for chip pin position

PinTraces toVoltage
1IC3 Pin 1
2IC2 Pin 38
3IC26 Pin 3
4R18 Right
5IC26 Pin 5
6IC26 Pin 6
7R17 Right
8IC26 Pin 8
9
10
11
12R19 Right
13IC26 Pin 13
14IC26 Pin 14
15IC26 Pin 15
16IC26 Pin 16