Sinclair ZX80 / ZX81 / Z88 Forums

I don't have a scope right now or I would take a look at what the ZX81 signal looks like just before, during, and after vblank. Is it a flat line, or are there spikes in it? Out of interest.

Well.... I put it in Audigy and found that the "chirps" are 6500 hz tones at 50 times per second. This 50hz repetition must be related to the retrace at vblank. A total guess but there may be some regular pattern of black scanlines drawn offscreen in the overscan area at the beginning or end of the ...

Tested tape saving tonight. It was a real P.I.T.A getting a usable audio file recorded; When I made my video amplifier, I used a direct input to the transistor with pullups to +5v and pulldown to GND to set the voltage. I think it attenuates too much of the ULA output, reducing the MIC level. The am...

The 81 was meant to be used with the "shoe box" type cassette player recorder, using the earphone socket for loading which as you may appreciate has a reasonable amount of "punch". One method that has been suggested By f/m 1024MAK is to send your WAV into say a pair of PC desktop speakers then run ...

It is also important to note that the 7805 voltage regulator is very good at ‘cleaning’ the noise and ripple from the +9V (nominal) input, but if the electrolytic capacitor(s) in the Sinclair ZX PSU (or equivalent) are life expired, then the 7805 can’t fix that. In a normal situation, for normal us...

Thank you. I managed to get the method on the German page to work, and even the 32k using an AND gate. The issue seems to have been with the 62256 I initially used. The SRAM may have been bad, or at least didn't want to play nicely in the ZX's environment, even though the TL866 tested it as good. I ...

Indeed I have a board that says "ISS 3" in the corner. So the connections are the same on your earlier one? Nice! What happened to my post was that I edited it, and being new each post (or even edit) requires administrator approval, so that caused my post to disappear while pending that approval. It...

I added a 33uF electrolytic cap across the +5VDC and GND near the regulator to get rid of some video noise. It also reduced the intensity of the vertical grey bars by about half. I imagine a larger cap would help even more so, as the bars are relatively low frequency. I was surprised to find the ZX8...

Success! It worked with a 84256 SRAM. For some reason, the 62256 just wasn't happy.

Thank you for your reply. I left pin 27 in the socket, so it is still attached to both /WR and the pullup. I've also tried removing the pullup as it's optional if you don't want to use the hires scheme. Pins 1,2,22,23, and 26 are all isolated by bending out the pin, with the connections made by wire...