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RogerEvans · 2nd Jan 2020, 4:26 pm

I agree with Chris, the regular pattern on the screen looks the CPU has not initialised the video memory, either because the memory is bad or the CPU is not running. The 4116 DRAM chips have three power supply lines, all of which have to be correct. Pin 16 is ground, pin 9 should be at +5V, pin 8 at -5V and pin 1 at +12V. You could also check pin 26 (Reset) on the Z80 CPU which should be at +5V but might be low if the reset timing capacitor has become leaky. Other checks on the CPU really need an oscilloscope.

I don't have a Spectrum myself but the schematic diagrams on the Web seem to show that the first 16k of memory was generally using 4116 ICs. Later generations of DRAM were single +5V only.

Regards,

Roger

2nd Jan 2020, 4:26 pm	#5
RogerEvans Hexode Join Date: Oct 2014 Location: Wiltshire, UK. Posts: 381	Re: Spectrum advice I agree with Chris, the regular pattern on the screen looks the CPU has not initialised the video memory, either because the memory is bad or the CPU is not running. The 4116 DRAM chips have three power supply lines, all of which have to be correct. Pin 16 is ground, pin 9 should be at +5V, pin 8 at -5V and pin 1 at +12V. You could also check pin 26 (Reset) on the Z80 CPU which should be at +5V but might be low if the reset timing capacitor has become leaky. Other checks on the CPU really need an oscilloscope. I don't have a Spectrum myself but the schematic diagrams on the Web seem to show that the first 16k of memory was generally using 4116 ICs. Later generations of DRAM were single +5V only. Regards, Roger