This is the CAS signal (can't remember but I think its IC12):
And this is IC18:
Yeah, im using the Modulator. Apologies for such a stupid question as thats the goto point on the Spectrum (or the heatsink) but the weirdness around how the regulator is used worried me a little. In the end I just went for it!! Im currently using a brand new 9v 1a PSU which I bought specifically for thisthat is mains earth isolated. I do plan on switching to my bench PSU which I can and have setup to be mains earth isolated but I don't have a suitable lead and I haven't found a PSU that im willing to sacrifice to get one yetmikeb wrote: ↑Wed Nov 20, 2019 6:46 pmYou must've found ground The case of the modulator is a big shiny ground. Just be aware that the PSU you are using to drive Oric must be (like the original wall wart) isolated from mains earth, otherwise applying the (no doubt earthed!) probe of the scope to the board will bypass the regulator. This is not a problem for old style transformer wallwarts, or most modern switch mode replacements, but is a potential problem if you are using a bench supply or other metal cased PSU, often ground of supply is mains earthed. That doesn't work with Oric when you start introducing other earths!
I didn't check all the lines again tonight (getting very late) but when I did last night, they were all pretty much the same, though some where a little flatter than others, but all up at the same level. I'll check them again tomorrowmikeb wrote: ↑Wed Nov 20, 2019 6:46 pmAddress line, always high .... that's interesting. Assuming the ROM gave up a startup vector, code would be running in ROM area (#C000-FFFF) which means you can forgive A15,14 being high. A13 downwards should be moving about (high and low). Otherwise, if they are all high, all the time, that's #FFFF .... can you make sure all 16 are not stuck high?
What is pin 7 (SYNC) of the CPU (6502) doing? IF the 6502 is fetching/decoding/executing, this pin will be toggling high/low. You may need to watch it at power up, if you can, to see what it does (because it might be that the CPU is crashing very early on, see my comment about all-reading-no-writing).
I tried to capture the output on startup but couldn't get the scope to trigger for some reason. But this is what I normally see:
To be continued...