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skiselev / omega

Omega Home Computer
GNU General Public License v3.0
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Bizarre signals with no video out #53

Open ProfsRetroFix opened 3 months ago

ProfsRetroFix commented 3 months ago

Welp, as I don't have an MSX.org account I'm running out of places I can hopefully get a bit of guidance on this.

I'm trying to build an MSX Omega, and failing on smoking test 2 on MSXMaker's step-by-step guide. Test one works with flying colours. However, test 2 doesn't give me a video signal. At all. No black screen, nothing. BIOS-wise at the moment, I'm using the one from the link, with a halt BIOS in the first have, and NTSC C-BIOS in the second. I don't think the NTSC BIOS should be the issue though, as the reason I flashed the halt BIOS ROM is because this was happening with the PAL BIOS too.

I've wired it for PAL (although if NTSC is easier, I might change it because this obviously isn't working), and the frequencies don't seem right. SCIN on the CXA1645P encoder doesn't look right either. It's just constantly at around 2.4v, no pulse.

I've attached some screenies from when I was taking some measurements. I'm hoping someone can lead me in the right direction here. This was a fun project up to this point, and now I want to throw it out the window. I've examined every solder joint, and they seem to be fine (although admittedly I haven't gone over them with a multimeter yet). I've built a retro chip tester pro from scratch though, and recapped a few machines, so hopefully my work isn't that bad.

In case of fake chips, I've already spent an extra €80 getting a couple of replacement CPUs and V9958's from UTSource. Doesn't seem to make a difference. I've got a couple of replacement CXA's coming just in case. Everything else is new from Digikey and Mouser.

Does anyone have any ideas of where I can go from here?

CSYNC on the VDP is reporting at 15.70 kHz. My oscilloscope can't seem to lock onto a frequency like it does for SYNCIN on the CXA later. image

SCIN on the CXA1645P seems to be held at around 3.2v? Is this normal? I was under the impression it should be pulsing. image

SYNCIN is showing at 16.235 kHz, the oscilloscope can lock in this time. But it's still not the PAL frequency. What's going on here? image

zomgugoff commented 2 months ago

Per the CXA1645 datasheet, SCIN should be a sine wave or pulse from 0.4-0.5 VP-P. I'm seeing the system clock coming in at 3.58MHz on mine. Something is wrong there.