Sinclair ZX80 / ZX81 / Z88 Forums

I can’t think of an easy way unless you have an expensive logic analyser with enough inputs to trace all the signals on that ZX8401 chip. Because the ZX8401 does all the multiplexing for all the DRAM from the Z80A side, if this chip dies… However, the ULA does not use the ZX8401 when reading the DR...

Hi, this is a CZ Spectrum Plus IMG-20210807-WA0040.jpeg an Argentinian Clone of the ZX Spectrum 48+. Board is very similar to Sinclair's ISSUE 6A and uses the ZX8401 / PCF1306P multiplexor . 2021-8-8 2-13-7.jpg Sadly it doesn't work. Looks like ram is not being read. I suspect the multiplexor is bad...

Wow.. thats a piece of work..
Why didn't you use the conectors you ha e desoldered from the board to attach to the ribbon /membrane?

jsweinrich wrote: ↑Tue Jul 20, 2021 3:10 pm Thanks all. Although I developed a great method to connect to the trimmed ribbon cables using conductive adhesive copper foil my keyboard was damaged inside... So, yea, I ordered one...

Would you share it with us?

Thank you for your work on EightyOne.
And glad to hear you had a god recovering..

I was hoping some could provide a method to remove the plastic covering from one side of the ribbons to exposed the conductors of a shortened ribbon. Do you mean inside the keyboard?? Those tracks are not easily repaired... silver paint is useful:useless::50:50 and expensive.. I ve seen some one to...

XavSnap wrote: ↑Wed Jun 30, 2021 2:23 pm Hi,
The blue screen mean "No Signal" !
Something's wrong with the ULA ?

Some TV detect the loading screens as "no signal".. and some are able to deactivate the blue screen in the menu.. most now don't

May be too loud?

Hello MARK, I was reading other posts these days and had come to a similar conclusion. So I left the transistor alone. Pin 17 of the Z80 is pulsing. I tried another ULA and another Z80 with no change. I removed the ROM and there was no change either. The RAM had already been tested in a TK90X (spect...

Well this is a TK85, a Brazilian clone with 16Kb internal RAM and a rubber keyboard so I think it is more like a TS1500 clone, Rom is not identical as have some differences but compatibility is almost 100%. This particular model has a Ferranti ULA, pin 22 is grounded so it runs at 60Hz (Brazilian PA...