Sinclair ZX80 / ZX81 / Z88 Forums

Well done!

Mark

Hello and welcome to our forum rcmolina!



I hope you enjoy the forum

Mark

Is it possible that one of the traces is damaged? Yep, that’s what I was getting at! It is possible to test for that by using the continuity range or the 200 ohm (or equivalent) resistance range on your multimeter. Do the tests with the power disconnected from the computer. Put the negative (black)...

For the ZX81 ROM content, you need a 64K bit (8K bytes) EPROM such as a 2764. But these have been obsolete for many years. You can also use a 128K bit (16K bytes) EPROM such as a 27128 or 27C128. Alas these are also now obsolete. You can however have the ZX81 ROM code in the first 8K bytes and your ...

Well done 👍 :D The 74LS157 are multiplexer chips to switch between the 14 bit address from the Z80 to the two lots of 7 bit addresses used by the DRAM chips. I don’t know why there are extra resistors fitted to the Memotech 16K RAM pack in that photo. They were not present on the unit that I took ap...

I THEN decided to check at IC6 and got 8v at ground ! Measured again and got 0v, measured again and got 7.6 and rising, then 0v again Now I just need to figure out WHY ! I suspect a faulty ram module leaking volts to ground ? Hmm, what point are you using for the negative lead (black probe) for you...

wietze wrote: ↑Fri Jul 10, 2020 4:39 pm Would you be able to point me to some more in depth resources regarding this?

Read Wilf Rigter’s Video Tutorial first

Note: by default the pages at the linked to web site may not display correctly, so switch your character set to "western" for correct display.

Mark

It maybe worthwhile mentioning that a user program (BASIC or machine code) will only run at the maximum MPU speed if the machine is not generating a display, this is known as FAST mode. This is the same as the system used by the ZX80. The normal ZX81 mode is SLOW mode, also known as compute and disp...

Oh, since I forgot to welcome you, let me do that now...

Welcome on board Rob!



Welcome to Sinclair ZX World

Mark

Oh, my bad, I forgot to welcome you

Time for me to correct that, so...

Welcome on board JetSetWally!



Welcome to Sinclair ZX World

Mark