Sinclair ZX80 / ZX81 / Z88 Forums

dr beep wrote: ↑Fri Mar 08, 2024 2:07 pm I WROTE THE GAME

Possibly cross wires... I'm just saying that I use this one of your games because it's a quick load via tape, to check that high res is working after I've done a RAM mod.

I'm not dissing the game, or your fine work in any way, shape or manner.

msknight wrote: ↑Fri Mar 08, 2024 1:50 pm In case it matters for the price of fish, here's the clock as going in to the processor...

That is exactly I would expect.

Mark

I must have bought the wrong ram chips... again.

Here's someone using Hitachi HM62256LP-12 and using high res without needing a capacitor.
https://newstuffforoldstuff.blogspot.co ... grade.html

Unless berzxerk is pseudo high res.

AFAIK Berzerk is pseudohires

Those -12 are faster access times than the -15 I already bought, so I'm not going to spend more money on faster chips than the ones I'm already trying to slow down

But... I really don't know where to go from here.

Do I need the 10k resistor between 27 and 28 for this chip?

Doesn't matter- I tried it anyway... didn't change anything

I don't think it's the RAM.

I attached a ram pack that I've converted to high res and the same thing happened. I was monitoring the chip enable and it stayed at 5v to the on-board RAM.

I swapped the ULA and the same thing.

The processor and ROM are soldered, so I'm a bit cautious about my next move.

As you can see, nothing too awkward about the board. Converted to lumacode RGB-HDMI, tape and power jacks have been replaced. Two main caps have been replaced. Voltage regulator replaced. ULA has been socketed and the RAM has been replaced with teh chip and roughly wired in to the pins, with the two pin socket for temporary cap fitting.

My head hurts.

I think something is going wrong with the, "stealing," process and it's a matter of timing... but I'm not sure where to point my scope probe and what I'm looking for, as the "how to"s I've been reading as to how high res graphics work, aren't helping to point where I need to be looking, other than the refresh line.

However, looking at the circuit diagram, I can't see how that is being used by the ULA to "hijack" the data.

Can someone point me to something that will help me work out where I should be looking please?