exxos's Atari, Amiga & retro forum

I bought some weeks ago the 16Mhz ST booster (rev. 1.4) along with a Mega ST DUALTOS PCB from Exxos and installed everything in my last toy, a Mega ST 2.

I have performed all the mandatory fixes except the 1772 pull ups.

My Mega ST boots fine in TOS 2.06 and behaves normally until I turn the blitter on, where it freezes.

It also displays four bombs when I want to access the FDD drive, with a disk inserted in, no matter if it is the original FDD, HXC or Gotek. Accessing the FDD with no disk inserted shows the usual warning message.

It was the same situation before I replaced the original SILS with 2.2K ones, so it is obviously not a bus resistor related issue.

Just for information, my machine works fine with the original CPU and the blitter on (and without the blitter patch).

I suspect the DMA needs some kind of buffering, like on the STEs, but I am not sure.

I will try to add the blitter patch on the booster and check if at least the blitter issue is solved.

Exxos does not support this booster on original motherboards, but if you guys have any clues or suggestions, they are welcome.

Under TOS 2.06 4 bombs generally is a floppy problem, for example if you boot a TOS 2.06 machine with no floppy you'll get 4 bombs. I suspect in this case you may have some timing issues.

You didn't say, but are these problems happening just at 16Mhz, or at 8Mhz too?

If you had a blitter patch, did you repair the cut track under the cpu? Also what blitter exactly? Are the solder pads fully broken when blitter fitted?

rubber_jonnie wrote: 13 Jul 2021 15:37 Under TOS 2.06 4 bombs generally is a floppy problem, for example if you boot a TOS 2.06 machine with no floppy you'll get 4 bombs. I suspect in this case you may have some timing issues.

You didn't say, but are these problems happening just at 16Mhz, or at 8Mhz too?

I did not try to run my Mega ST with the booster at 8Mhz yet.

Something worth checking though...

exxos wrote: 13 Jul 2021 16:18 If you had a blitter patch, did you repair the cut track under the cpu? Also what blitter exactly? Are the solder pads fully broken when blitter fitted?

Yes , the track under the CPU is repaired.

The blitter is a SGS 8937.

If you mean the two blitter enabling/disabling solder pads, they are not soldered.

HigashiJun wrote: 14 Jul 2021 05:30

rubber_jonnie wrote: 13 Jul 2021 15:37 Under TOS 2.06 4 bombs generally is a floppy problem, for example if you boot a TOS 2.06 machine with no floppy you'll get 4 bombs. I suspect in this case you may have some timing issues.

You didn't say, but are these problems happening just at 16Mhz, or at 8Mhz too?

I did not try to run my Mega ST with the booster at 8Mhz yet.

Something worth checking though...

With any booster I'd always recommend testing at the original CPU speed first. That way you can verify it is working under standard conditions.

HigashiJun wrote: 14 Jul 2021 05:30 I did not try to run my Mega ST with the booster at 8Mhz yet.

You need to try that.. There was a buffer board for the mega I now remember because the clocks were really bad.

see MEGA ST BUFFER BOARD INSTALL - MUST FOR ALL MEGA ST!
https://www.exxosforum.co.uk/atari/last/ ... /index.htm

but I have not made if for long time..

rubber_jonnie wrote: 14 Jul 2021 09:30

HigashiJun wrote: 14 Jul 2021 05:30

I did not try to run my Mega ST with the booster at 8Mhz yet.

Something worth checking though...

With any booster I'd always recommend testing at the original CPU speed first. That way you can verify it is working under standard conditions.

And that is a wise recommendation...

exxos wrote: 14 Jul 2021 09:57

HigashiJun wrote: 14 Jul 2021 05:30 I did not try to run my Mega ST with the booster at 8Mhz yet.

You need to try that.. There was a buffer board for the mega I now remember because the clocks were really bad.

see MEGA ST BUFFER BOARD INSTALL - MUST FOR ALL MEGA ST!
https://www.exxosforum.co.uk/atari/last/ ... /index.htm

but I have not made if for long time..

Yes, I also heard that some Mega STs might be affected by with unstable bus issue.

But it seems there is no way to get the buffer board anymore... :cry:

You probably only need a Schmitt buffer on the 16mhz... But you need to be stable in 8mhz before moving onto other things.