The Sinclair QL (for Quantum Leap) is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the ZX Spectrum.

The QL was aimed at the serious home user and professional and executive users markets from small to medium-sized businesses and higher educational establishments, but failed to achieve commercial success.

While the ZX Spectrum has an 8-bit Zilog Z80 as the CPU, the QL uses a Motorola 68008. The 68008 is a member of the Motorola 68000 family with 32-bit internal data registers, but an 8-bit external data bus. 

Wikipedia Sinclair QL

TroubleShooting

Power-on problem: White screen, possible faulty RAM memory.

I recommend installing the "Minerva" eprom, FW developed to give a new basic, but above all to help turn on the QL. Remove the two original EPROMs and insert the socket with the new EPROM.

                                                        Wikipedia Minerva 

in case of error a screen like this will appear. This window tells us that the first line is the value that is written to RAM, the second line is the read value, the third is the memory address.

In this case, a little program developed by XAD at this address comes to our aid: https://www.nightfallcrew.com/minervaram/index.php
We enter the data and we will have an indication of the faulty RAM. In our case the U4.

IF < $30000 (ADDRESS) = IC8  ,IC7  ,IC6  ,IC5  ,IC4  ,IC3  ,IC2  ,IC1

IF > $30000 (ADDRESS) = IC16 ,IC15 ,IC14 ,IC13 ,IC12 ,IC11 ,IC10 ,IC9

IF > $40000 Faulty ram is in expansion memory.

 Here we can see the operation after the repair.