Sinclair ZX80 / ZX81 / Z88 Forums

Two things:

The Opus has its own bank switched / paged ROM/RAM system, so there must be a switch or something to prevent clashes between them.

The MF1 looks to be missing a lot of logic chips.

Mark

I'm guessing, but I would have thought that if the RAM was faulty, you would get different symptons. Is it really permanently soldered to the Speccy :shock: That makes it awkward... Have you checked for solder splashes and short circuits? Also open circuit / bad connection issues? This site has some...

If it's any help, the ZX Spectrum issue 1 (and some early issue 2) boards that have a different "dead bug" daughter board tend not to be modified (unless they were back in the day). You don't need to snip any wires. Just desolder the two wires going into the modulator from the PCB and secure them so...

Hello and welcome :D The first point is that the keyboard is a matrix of eight half rows (five keys in each half row) and five "columns" (eight keys in each column). Hence there are two groups forming the connection to PCB (one of eight and one of five). A hairline fracture in one of the metal layer...

Hmm, being the electronics nerd that I am, I was thinking that those are a useful source of a couple of 74 series logic chips... :ugeek: :twisted: :lol: Mark PS i have plenty of run of the mill issue 1 and issue 3 boards to tinker with. A long time ago in a universe far, far away, I bought around 5 ...

Either by design or by mistake, the NMI handler in the BASIC ROM will result in the Z80 jumping to the reset vector. With a MF1, it should switch out the BASIC ROM (forcing /ROMCS high) and page in its own ROM. Hence during the NMI it's the MF1 ROM that should be in control.

Mark

Sounds (!) like you are nearly there with a working machine. Well done

Mark

Okay.

All those require the machine to page out the internal ROM chips. Do you have any other expansions/interfaces to try, such as a Kempston (or compatible) joystick interface?

Mark

Some important things you need to know about the type of Ferranti ULA chips used in Sinclair computers: They use a type of bipolar transistor technology. This is very different to the other large chips used in the ZX Spectrum. The matrix cells (that provide the logic functions) are CML (current mode...

Which expansion cards / interfaces have you tried?

Mark