exxos's Atari, Amiga & retro forum

My eye has been drawn to the Mega ST's expansion bus of late.

I was reading the scanned documentation which makes reference to the physical dimensions "see figure 1/2".

Sadly figures 1 and 2 did not make it to the scan.

Does anyone know a reference for the mechanical drawings of a card suitable for fitting in the megabus slot, or is it a case of getting my ruler out?

Ta,

BW

Judging by the existing cards, you only need to pay attention to the battery slot and the pillars supporting the case.

It seems ideal for a Riebl card
but one like Maxon will also fit.

Thanks @artik-wroc,

I was thinking in terms of height offset from the socket and the alignment needed for supports and the rear hatch.

I can do it by inspection from a 'Sound Acclerator' board I have, but I was hoping for some proper numbers off the drawings.

Cheers,

BW

The latest Megabus card to be manufactured is the ATW800/2 (2024) so I could imagine you could ask them?

https://www.geekdot.com/atw800_2/

Just bumping this again as conversation over here has rekindled my apetite for some megabus work.

Would anyone with one of the new ATW800/2 adapters or another rear-penetrating Megabus card mind doing some measurements for me? Perhaps @mrbombermillzy, you could measure the sound accelerator card?

I'm looking for overall dimensions, positioning of the megabus socket relative to those, height of the board above the megabus socket and any support hole positions, if possible.

Ta.

BW

Mine is on my desk at the moment and I have a pair of large digital calipers. What dimensions did you want?

Badwolf wrote: 08 Sep 2026 10:07 Perhaps @mrbombermillzy, you could measure the sound accelerator card?

Im happy to oblige:

When photographing - as the card isnt flat - it skews the perspective distance between card edge and measurement notch, so its better to give actual dimensions here. :)

The card measures 140mm from backplate to end of card.
135mm width.
The backplane thickness or height is 28mm.


Let me know if theres anything Ive missed off the photos and I'll measure it up for you. ;)

mrbombermillzy wrote: 08 Sep 2026 14:59 Let me know if theres anything Ive missed off the photos and I'll measure it up for you. ;)

Lovely, thanks!

This is all just a first approximation for now for a prototype so with any luck that'll be plenty.

BW

No problem. Cant wait to see what you are up to here. :D

alexh wrote: 08 Sep 2026 12:41 Mine is on my desk at the moment and I have a pair of large digital calipers. What dimensions did you want?

Hi Alex, first approximations for a prototype board really, so:

overall dimensions, positioning of the megabus socket relative to those, height of the board above the megabus socket and any support hole positions, if possible.

Mrbombermillzy's given me the rough figures. If you are able to refine them any more, please go ahead. I anticipate the first board will be a proper prototyping one with lots of jumpers for research so if it's not perfect, that's fine, but hopefully I can get it close so the second version might actually line up!

BW