exxos's Atari, Amiga & retro forum

Hi All,

Finally managed to get my TF536 flashed with Atari ST firmware. However, on boot I get a rolling screen saying execution error 33 per attached screen shot.

Any ideas what I need to do to fix this?

Thanks

macsonny

The Mega is a bit finicky to use with TF536. Some have get it going and some have not.

Do you have TOS 2.06 running on your MegaST before installing TF536? I think you will need that or EmuTOS to use the ALT-ram.

If you read PAK86/030 manual you can find some tips on how to get a Mega more stable for accelerators. 80ns ram or better (I used 60ns on mine) and change the resistor array on data bus and adress bus. 4.7k on data and 3.3 on address.

You can also try changing the data bus drivers on the motherboard (74LS244 and 75LS373) for F-types instead. I didn't do that and my TF536 works.

You will need a stable and good PSU as well.

As well as the above, there are mandatory fixes shown here: Mandatory fixes which may help improve stability.

DoG wrote: 13 Apr 2026 15:28 The Mega is a bit finicky to use with TF536. Some have get it going and some have not.

Do you have TOS 2.06 running on your MegaST before installing TF536? I think you will need that or EmuTOS to use the ALT-ram.

If you read PAK86/030 manual you can find some tips on how to get a Mega more stable for accelerators. 80ns ram or better (I used 60ns on mine) and change the resistor array on data bus and adress bus. 4.7k on data and 3.3 on address.

You can also try changing the data bus drivers on the motherboard (74LS244 and 75LS373) for F-types instead. I didn't do that and my TF536 works.

You will need a stable and good PSU as well.

Thanks for the info. Good PSU and I'll look at the other suggestions. I'm running EmuTOS 1.3.

Excuse my ignorance but what is PAK86/030 manual?

Thanks

macsonny wrote: 14 Apr 2026 07:39
Excuse my ignorance but what is PAK86/030 manual?

PAK is another ST accelerator, they are pretty decent, I have an 020 version. There is a thread here about mine: PAK 68/20 Repository

Don't be surprised if the TF536 doesn't work though AFAIK it is quite old and not the best.

macsonny wrote: 14 Apr 2026 07:39 ...
Excuse my ignorance but what is PAK86/030 manual?

You can find the manual on dev-docs. Bus resistor placement. 9-pin bussed array.

rubber_jonnie wrote: 14 Apr 2026 10:37 Don't be surprised if the TF536 doesn't work though AFAIK it is quite old and not the best.

Old? Didn't terriblefire do the pcb in 2019-2020? Not that old in the grand scheme of things.

DoG wrote: 14 Apr 2026 15:46

rubber_jonnie wrote: 14 Apr 2026 10:37 Don't be surprised if the TF536 doesn't work though AFAIK it is quite old and not the best.

Old? Didn't terriblefire do the pcb in 2019-2020? Not that old in the grand scheme of things.

Actually my bad I was thinking of the TF534.

rubber_jonnie wrote: 14 Apr 2026 16:05 Actually my bad I was thinking of the TF534.

:lol: I figured you meant something like that.

So a lot of the advice I've gotten so far is to apply the various suggested fixes for the MEGA ST prior to progressing any further.

Looking through the list of what needs to be done it looks like the following:

1. Recap or replace power supply (DONE)
2. Use TOS 2,06 or EMUTOS (DONE)
3. Replace 5 x resistor networks with 2.2k resistor networks (IN PROGESS)
4. Replace reset capacitor (IN PROGRESS)
5. Recap main board (TO BE DONE)
6. Apply Blitter fix (NOT SURE)

Firstly is there any other fix I need to apply that I've missed?

Secondly, the Bliutter fix seems to apply only when the 68000 CPU is actually installed. As I need to remove the chip for the TF536, is there any other way to do the Blitter fix or is it not required when using the TF536?

Thanks

macsonny wrote: 15 Apr 2026 22:19 ...
Secondly, the Bliutter fix seems to apply only when the 68000 CPU is actually installed. As I need to remove the chip for the TF536, is there any other way to do the Blitter fix or is it not required when using the TF536?

I removed the blitter chip from the board as well as removed the blitter patch. According to the PAK manual the blitter is slower then <33MHz 68030 anyway. So it doesn't make much sense to keep it. Cool to have but hardly anything uses it. Same with FPU.

Some more info regarding blitter needed or not.

Thred when PhilC got his TF536 working in a Mega.