16mhz booster install in a mega 1

[RB80atari]

Morning folks,

I have a 2021 exxos 16mhz booster and tos 2.06 decoder here that i want to install in my mega 1.
I desoldered the old 68000 CPU and put it in a socket.
So im pretty sure all i need to do is remove the old 68000, install the booster with the new 16mhz compatible 68000 and then wire a cable from the 16mhz shifter pin hole on the booster (highlighted in red circle in my picture attached) to pin 39 on the shifter chip.... Is that it?

I did all of exxos mandatory fixes in advance of this as i know its recommended when using his booster
Also i still have the the blitter patch on my original 68000, now that ive done the mandatory fixes can this be removed? Should i keep it and use with the booster??

Im also using exxos 2022 mega st dual tos board.
I see that the earlier version of this board (2015?) needed a jumper setting for CE on the pcb and that it had to be wired to the booster, but it looks this newer version i have doesnt need any of that..?

Basically just double checking the install for this before i do it, i did see the guides but wasnt completely clear on it!
Cheers

booster.jpg

[RB80atari]

I forgot to mention im also using Exxos 4mb MMU Ram upgrade, with shifter adapter, not that it probably matters but thought id mention it.

For convenience im thinking i could wire the 16mhz wire to one of the solder pads highlighted in pic below. (Not sure which pin number 39 is without checking, might be on the other side of the adapter, but you get the idea..)

mmu ram.jpg

[exxos]

CE on the booster wires to CE on the dualtos PCB. You also need to remove the header pin on CE and fit the jumper link to select ROM bank.

[RB80atari]

booster.jpg

Cheers Chris, so just to clarify complete install (attached pic)

1) Run a wire from the pad on the booster pcb marked CE (marked purple circle, cant see under the top socket) to the dual tos board CE pad (marked purple circle)
2) Cut the leg off the header pin underneath the CE marked pad on the dual tos board (purple circle)
3) Wire a cable from the 16 mhz pad on the booster (marked in red circle) to pin 39 on the shifter chip....
4) Plug back in and hope for the best

Is that it? :D

[exxos]

Basically yes..

But you need to see what version blitter you have on this page..
https://exxosforum.co.uk/atari/last/MEGAST/index.htm
As really old version will give corruption.

Also note some mega boards have a series resistor in the 16mhz line to the MMU. This may or may not be important. Also you may have to experiments with the 16mhz feed to the booster.

Unfortunately the mega 16mhz clock is very bad and trial and error is the only way. It's also why I abandoned mega support as the problems were simply never ending.

[RB80atari]

OK Cheers, i got this shifter chip (mega 1)
pic of my board revision too
Is the resistor you talking about R150, mine is showing as 100ohm on the board?

Also wondering what to do with the blitter patch on the old 68000 with regards to the booster/ 16mhz 68000?
From what i read, i can probably just remove it?

Just reading the link you sent about the different shifter chips and note you say in your conclusions:


MEGA1 (REV 2.1) Will work with IMP or STFM chips at 8mhz. M5M44256BP-7 DRAM.
MEGA1 (REV 2.1) Will work with only with STFM chips at16mhz. M5M44256BP-7 DRAM.

MEGA1: The only time I needed the blitter patch was when one of the MEGA1's had /AS missing from the MMU. That machine only worked with IMP chips. When I hard wired a line from the MMU to the CPU it worked perfectly without the blitter patch and also worked with either STFM or IMP chips.

The MEGA1 will not work with IMP chips at 16mhz. I suspect as those chips are slower and twice as noisy as the STFM chips, that they do not work in the MEGA1 as Atari missed off the extra 2 DRAM buffers on the RAS/CAS/D0-7 lines. I suspect IMP chips work in the MEGA4 due to those buffers acting as a "noise filter".

So i guess because i have the IMP chips and rev 2.1 board, 16mhz is a no-go?
I also have a mega 4, a rev 5 board with this shifter (bottom pic), would it be worth trying that in the Mega 1?

The more i read about the issues with the mega 1 and imp chips the more i think i should just give up with using this booster, seems like a lost cause. Maybe my mega 4, rev 5 board would be a better candidate for this.

Thanks for the help

imp.jpg

mobo rev.jpg

shifter rev 5.jpg

[exxos]

Unfortunately, I can’t provide much more information than what has already been posted or documented. Many users have successfully installed the booster, including earlier revisions.

However, it’s worth noting that IMP chips often cause issues in some MEGA machines, as I’ve documented. These chips generate too much noise, making it difficult to run the bus reliably at 16MHz. The MEGA, like most ST models, has poor grounding, which cannot be resolved simply by adding a booster. The machine itself requires several fixes first, including the mandatory modifications.

I vaguely recall Atari mentioning that the MEGA could tolerate one IMP chip, possibly referring to the original STF machines—but I’m not certain anymore. That said, Atari did use multiple IMP chips in various machines, which led to solutions like adding a diode to the IMP 5V line on the DMA chip.

I eventually stopped investigating all the potential combinations because it became too time-consuming and wasn’t worth the effort. I only had a few boards available for testing, and while these issues are real, whether you encounter them will likely come down to luck. This unpredictability is one reason I no longer officially support the MEGA.

At the end of the day, it either works or it doesn’t. If it doesn’t, I wouldn’t be surprised given the many issues inherent in the MEGA. That said, since you’ve come this far, I’d recommend giving it a try. If you’ve completed all the mandatory fixes, you only need to connect two wires on the booster to test it. Let GB6 run for a few hours and see how it performs.

If it doesn’t work, the first step would be to replace the IMP chipsets. Beyond that, problems with the 16MHz clock could arise, depending on whether it has a series resistor or not. Unfortunately, I can’t recall the exact specifications or whether they vary between MEGA machines—you’d need to research that yourself if needed. I no longer have access to those boards.

Finally, the blitter patch is omitted, which is why using newer blitter versions is necessary to avoid data corruption.

[RB80atari]

Well, the booster doesnt work in my Mega 1 with all the mandatory fixes in place.
It gives 4 bombs before the memory test with TOS 2.06.
One time it started the memory test then after gave 4 bombs, sometimes it gives a whole row of bombs.
Sometimes there is corruption and bombs
dual tos 1.04 selected it gives 4 bombs (top pic)
1.04 another cool boot this time with corruption (middle pic)
2.06 4 bombs (sometimes gives corruption too)
What a waste of time..

104.jpg

104 b.jpg

206.jpg

[exxos]

You don't state what speed your running at. At 8mhz its likely a bad connection somewhere. At 16mhz is likely the imp chipset or problems with the 16mhz clock.

Also you will get 4 bombs in TOS206 without the floppy drive connected.

You also should try the CPU in the mega directly to make sure there is no track damage. A lot struggle removing the CPU and cause all sorts of damage. So best to test stuff methodology.

[RB80atari]

It was running at 16mhz with the gotek floppy drive connected.
CE pin cut and connected wire from the dual tos board to CE input on the decoder
16mhz connected from booster directly to pin 39 on the shifter
Continuity checked, all fine.

As soon as i removed the dual tos board and the decoder/booster and put the new CPU back in the socket on its own with the old TOS 1.02 hi and low roms, booted up fine first time and has given me no problems since.

You don't state what speed your running at. At 8mhz its likely a bad connection somewhere. At 16mhz is likely the imp chipset or problems with the 16mhz clock.

Also you will get 4 bombs in TOS206 without the floppy drive connected.

You also should try the CPU in the mega directly to make sure there is no track damage. A lot struggle removing the CPU and cause all sorts of damage. So best to test stuff methodology.