X68000 Super powers on, appears to be booting, no Audio/Video, !now working!

Started by chadti99, March 03, 2019, 09:50:07 PM

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Any ideas here? Unfortunately I don't get any video output either.  As soon as I flip the switch on the PSU around back it immediately starts the fan and the power LED is lit and I even get activity from the floppy drives.

What might be some good next troubleshooting steps to diagnose?

More Info:  All three main boards have been recapped, the power supply was recapped but not recently.

Update: I now have the soft power working!  Unfortunately still no audio and video.  I've only got an RGB Scart cable to test and I have it connected direct to my OSSC.  The OSSC is receiving sync signals between 31 and 15Khz but I only get a blank screen.  I've ordered a VGA adapter to test directly to a monitor.  I've also ordered a Pico PSU adapter.

Update 2: I had the system apart inspecting it once more, put it back together, and now I'm back up and running with Audio/Video!


Maybe it's time to replace all the capacitors if you haven't already. My XVI developed an issue where just flipping the hard power switch on the back on would make the green light in the front blink green and the PSU fan would start spinning even before you turned the machine on from the front. In my case, it still mostly worked so If I pressed the soft-power switch in the front, it would start normally, then after doing a soft-shutdown, it would go back to blinking green and still spinning the fan. After a full recap, the issue was solved, so it's possible your machine has the same issue. Not sure about the no video output though.


I should of mentioned that the capacitors have been replaced on all three main boards.

More info:
The Power LED lights green when flipping the switch on the back PSU
If I press the power button on the front the led remains green and my OSSC does confirm video sync over RGBS but I just get some flicker on the bottom of the screen

So the front power button appears to be working at some capacity.


It even appears to load games, Final Fight for example, if inserted into drive 1 and 2 sounds like it's going through the load routine. The OSSC even shows shows the sync change from 31khz to 15khz.


power on occurs for me when SRAM is blank. have you tried connect via vga cable to a pc monitor?


Quote from: leonk on March 04, 2019, 03:38:15 PM
power on occurs for me when SRAM is blank. have you tried connect via vga cable to a pc monitor?

I'm not sure what you mean exactly about the SRAM.  I went ahead and disconnected and reconnected all the data and power cables and removed/replaced the battery and now the soft power is working correctly!  I should probably change the title of this thread.  Unfortunately I'm still not getting audio/video.  I've only got an RGB Scart cable to test video so I've ordered a VGA adapter.  It's seems really odd that I can't get audio from the line out or headphone jack.


SRAM = BIOS.  Because the battery was dead, the real time clock was not working correctly.  The RTC is needed for a "healthy" soft power button circuit and as a result the system started on its own when plugged in.


As for video.. it could be anything, but there's 1 thing I posted awhile back that people still make a mistake with.


Just because a cable exists, doesn't mean you should use it or it's safe.  SCART RGB sync characteristics are CSYNC 0.3Vpp.  VGA sync characteristics are separate horizontal/vertical sync 5Vpp.

People are killing video scalars, splitters, video IC's in their X68000 etc. by feeding 5Vpp into something that's expecting 0.3Vpp.  Some knob many years ago thought it would be a good idea to take horizontal sync, and vertical sync, tie them together (without using a proper circuit!) and call it SCART.

The OSSC has a VGA port for supporting computers like the X68000.  Feeding X68000 into OSSC via the SCART connector (made for video game consoles) is just asking for trouble.  Get a proper VGA cable, plug into PC and see if you didn't blow the Video amp in the X68000.



Yes, that's essential and in my case I had to tweak some other settings on the OSSC to make sure the picture fitted the screen without any cutoffs.

I guess we should share and optimise our some settings and propose to add it to the OSSC wiki?


You have to Play with frontporch / backporch on the corresponding Resolution to fit the Picture without cutting the borders.


Lots of great advice here, the SCART cable I was using was indeed simply bridging the vertical and horizontal sync together.  I made my own VGA adapter and still no luck, no sync detected from OSSC.  I took some readings with my meter and came up with these results:

R: 0.65v
B: 0.65v
G: 0.65v

H sync: ~1.0v
V sync: ~3.0v

The voltages on the sync lines def aren't the 5volt I was expecting.  I'm thinking about ordering a SN74ALS05AN from digikey at this point.  Any thoughts, is this even a semi accurate test?


You can't use a voltmeter to check for the Peak to Peak voltages, they change too fast, you need an oscilloscope.  But I def. saw 5Vpp on a working X68K for HSYNC and VSYNC (I actually have 2 X68K computers and both showed the same values)


I wonder if something else is still not right? When my XVI had faulty video, it still played the sound. Games would boot, and the music would play via the internal speaker.


If you can't get it working I could look at it for you, send me a pm


I'm back up and running again guys!  I'm not entirely certain why, I haven't made any changes other than removing the main boards again for inspection and reassembling.  I'm using the VGA cable I made connected to an OSSC and the picture is so crisp!  It's good to be back!  Thanks for all the support guys!


Had this issue. Appears to be caused by dirty/broken contacts on the power connector or cold solder joints on the daughterboard power supply header