Re: Atari Mega ST 1 Rev 1 no boot
Posted: 27 Feb 2025 15:50
I like the design. I assume the other lead plugs into the ROM sockets to provide the datalines?
BW
BW
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I like the design. I assume the other lead plugs into the ROM sockets to provide the datalines?
It's been a while, so I don't fully recall, but it isn't plugged into the ROM sockets, but some sockets on ICs next to them:Badwolf wrote: 27 Feb 2025 15:50I like the design. I assume the other lead plugs into the ROM sockets to provide the datalines?
BW
Ah yes, of course. The ROM would be on the wrong (CPU-side) databus.rubber_jonnie wrote: 27 Feb 2025 16:21 It's been a while, so I don't fully recall, but it isn't plugged into the ROM sockets, but some sockets on ICs next to them:
I think U35 and U32 which are 74LS244's which are buffers. The rest i.e the small board replaces the resistors.
IIRC they had pin headers or sockets on top of them, not great. I didn't need to replace them when I removed the mod, so I think mine at least were ok. Doesn't mean they all will be.Badwolf wrote: 27 Feb 2025 17:05Ah yes, of course. The ROM would be on the wrong (CPU-side) databus.rubber_jonnie wrote: 27 Feb 2025 16:21 It's been a while, so I don't fully recall, but it isn't plugged into the ROM sockets, but some sockets on ICs next to them:
I think U35 and U32 which are 74LS244's which are buffers. The rest i.e the small board replaces the resistors.
Shame it didn't work, but could that bit a hint: are those data buffers functioning properly after the removal?
BW
Left it for 5m and nothing. I think next step is to analyze serial output, already ordered a cableDoG wrote: 27 Feb 2025 10:53 Have you left the computer booting for like a minute? It takes a pretty long time for it to show desktop if no disk or drive is attached.
Did you remove the small adapter board? Mine wouldn't work until I did so, no RAM.
Yes, same here … no ram until all resistors went back to their original place in motherboardrubber_jonnie wrote: 27 Feb 2025 23:04Did you remove the small adapter board? Mine wouldn't work until I did so, no RAM.Dwh18 wrote: 27 Feb 2025 22:33
Left it for 5m and nothing. I think next step is to analyze serial output, already ordered a cable
Great.Dwh18 wrote: 28 Feb 2025 06:55Yes, same here … no ram until all resistors went back to their original place in motherboardrubber_jonnie wrote: 27 Feb 2025 23:04
Did you remove the small adapter board? Mine wouldn't work until I did so, no RAM.
Quick question.... serial output only works with Diag cart on right? or a regular boot should show some output?rubber_jonnie wrote: 27 Feb 2025 11:41Definitely looking like a RAM issue. I'd definitely recommend using a serial cable, it will tell you an awful lot about the RAM during boot.Dwh18 wrote: 27 Feb 2025 11:22
Yes, different behavours with Hi and Lo Res .... Diag only loads in High Res monitor, and previous RAM error (white border whith black screen) only appeared in Low Res monitor, so RAM error I think it's done. the only patch I can see now on the motherboard seem's to be related with FDD I'll try to remove it and check behaviour. Tks!
One thing I would add here is that the Mega ST mainboards are pretty fragile, so handle with care, I had one board where I plugged an IDE adapter into the MegaBus connector and it popped 2 vias and broke it.