Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

[ILAH]

Do you mean 100 nF is still to high, or over 300 nF. When I tried 10 - 100, always the same result / pic1.

I did a 16k mod on another machine with the same SRAM chip. Here the WRX hires works regular, so i thaught the problem would be the additional 32 k / 7400 part.

[Flatulentia]

Yes. 100nF is far too high.

As Mark said, what you're trying to do is shift the RAM timing to within a window where it behaves as expected by the rest of the hardware.

If no value between, say, 33pF and 470pF fixes the problem then going higher will likely achieve nothing except placing unnecessary load on the ULA's /ROMCS pin.

[ILAH]

Corrected to pF which i used. I have not used nF caps.

I checked my other mod and post a picture below. Here i us a 100 pF cap. The result is a correct display of WRX graphics.

[1024MAK]

If you want to try without the NAND logic gate (74LS00) in circuit, disconnect the wire to pin 1 of the SRAM chip. Now connect pin 1 of the SRAM to either a +5V point or to a 0V/GND point.

Mark

[ILAH]

Maybe i will go back to 16k mod. But my goal was to have 32k with WRX possible.
For today i will give up. Thanks for your advice.

[Lardo Boffin]

Corrected to pF which i used. I have not used nF caps.

I checked my other mod and post a picture below. Here i us a 100 pF cap. The result is a correct display of WRX graphics.


mod16k.jpg

Ooh. Another yellow / beige zeddy with a 622 ROM (https://www.sinclairzxworld.com/viewtop ... 236#p47236). Any idea what date code the ULA has?

[ILAH]

The original ULA was DOA and has been replaced. Here is a pic of the bottom of the dead ULA. The top is glued to the heatsink forever.

[attachment=0]IMG_9383.jpeg[/attachment