Sinclair ZX80 / ZX81 / Z88 Forums

Thank you all for your excellent guidance! The SRAM module indeed seems like the best way forward. I'm actually quite surprised that those 4116s have lasted so long on this dodgy power supply. The -5V should power on first and power down last for the 4116s, but that's not respected here at all. Sinc...

I'll be repairing a friend's ZX Spectrum (Issue 4), which started misbehaving one day. Voltage measurements indicated that the -5V was being shorted to ground. The scope also showed that the low RAM data signals were garbled. So, some of the infamous 4116s have blown. I plan to desolder and test the...

Thanks! I'll need more study because I haven't seen the light yet. I can sort of understand how the Z80's control signals (/RD, /RFSH, /MREQ) are being decoded because of the peculiar video subsystem. In "Thanks for all the memories" A13, A14 and A5 are connected both to A, B and C and U2a and U2b f...

Thank fellas! Glad to be here!

Several of Wilf Rigter's designs use an improved memory decoder based on a 74HC251 multiplexer: Thanks for all the memories , ZX RAM I/O , ZX97 Lite . I'm puzzled by the switch that allegedly swaps the 8K block in the address space of 0-8K in ROM with the block in 32-40K in RAM. If I understand it c...

Hi all! My journey into the mysterieus ZX world began about two decades ago when I was a kid of about 15. I had been getting into programming my own stuff for a few years back then. That magic feeling when you learn to make a machine obey your wishes! :) One day Dad showed me his ZX80, which was his...