Sinclair ZX80 / ZX81 / Z88 Forums

Mark, for TR1 and TR2 on this Spectrum with poor colors on display (especially the yellow which is very poor) I confirm the signals are 0.2V different ( 0.2V lower) from another ZX Spectrum (which has a very good video signal). I measured around 1.40V for my working Spectrum, only 1.20V for this "de...

Up anyone ?

After having wait for about 25 minutes, here is the result :
the red things, which appear on the blue columns, flash every second :
the columns are totally blue for one second, then the red appears on them for one second, then the columns are totally blue for one second, and so on ...

The red, on the blue columns, moves.
I will now try to let it run for 30 minutes.

Here is the photo of the display without ROM :

I don't know why, but now the display changed a bit : https://zupimages.net/up/20/17/3kgb.jpg About the Z80 tests, on pin 6 I see a signal. But on all other pins you asked to test, no signals ! Yes, if I power down/up the Spectrum, sometimes the grey border becomes black (but it is most of the time ...

Thanks Mark, but before you posted you message I already desoldered every RAM from my working issue 4S board to connect them to my non-working issue 2 motherboard. Result : same ! All I can say is that there is some kind of sensitivity : in a whole working set of 8 RAM chips, some RAM chip will be n...

I have put all the RAMs on sockets. The problem was the same before replacing them and putting them on sockets. IC3 and IC4 have been replaced. About the 4116 RAM, I must admit that sometimes I think about maybe my RAM sets are bad. But I tested with 4 different sets of RAM : - 2 sets of MOSTEK RAM ...

Hello all, here is my 3rd Spectrum, not working at all. When I power it up, here is what is on the screen : https://zupimages.net/up/20/17/cz8b.jpg It has an issue 6A motherboard. I already replaced many parts on it : - Z80 - ULA (IC1) - PCF1306P (IC27) - all the lower RAM - 74LS04N (IC28) - TR4 and...

Mark, no problem, I understand, thanks a million for your time to help me ! - IC14 pin 17 shows a very regular 4.43 MHZ waveform (2.80V) - IC14 pin 2 and 4 show no waveform, 0V. - IC1 pin 13 shows 3.20V About TR1 and TR2, yes, on this Spectrum with poor colors on display (especially the yellow which...