Fixing a poorly ZX-Spectrum (Part 4)
I’ve now established that D1 on the data bus is being held low. The only chips on that line are the Z80, the ULA, the ROM and the RAM chips IC7 & IC16. The plan is to take each chip out of the equation by temporarily disabling them one at a time and then testing the bus for normal operation. I will start with the 4116 chip IC7, then IC16, then finally the ROM, the …