Exxos 4MB ram upgrade on a Mega 1 (had a Marpet)

[RB80atari]

Hi folks,

Hope everyone is doing well.
New member here, just wanted to say hi and see if see if i can get some help and advice upgrading my Mega 1.
I bought a few upgrades from the exxos shop, the dual tos (1.04 / 2.06) decoder/booster with the new CPU and MMU ram upgrade amongst other things. I'll be doing the upgrades one at a time.
The first upgrade i want to do is the ram, i got the Exxos 4MB MMU type.

My Mega 1 had a Marpet ram upgrade installed which ive just removed, i downloaded the installation manual for it just to check what they did to install it and i see that they had to cut some resistors on the motherboard and rewire them to nearby 5v on a capacitor to turn off the memory banks on the motherboard.
Looking on my Mega 1 i can see that indeed, resistors R148 and R149 (Bank 2) and R68 and R70 (Bank 1) have all been cut and rerouted to 5V on the capacitor, i assume deactivating all of the 1MB onboard memory on the motherboard and just using the 2MB on the Marpet.

So i guess i have 2 questions about the Exxos ram install:

1) What to do with the motherboard ram with the new Exxos 4mb upgrade, do i leave it as-is, with all motherboard ram disabled from the Marpet upgrade and just go ahead and install the new exxos MMU ram upgrade? Or do re-enable onboard ram by reattaching (or changing) the 4 resistors back onto the motherboard and disconnect them from 5v on the capacitor?

2) My shifter is in a socket, so aside from installing the shifter into the Exxos shifter adapter board and putting that in the socket and then installing the Exxos ram MMU adapter board into the MMU socket and connecting them with the thin connecting cable, is that all i need to do, nothing else?

Thanks for the help :)

Cheers, Bob

Here is a pic of my motherboard, progress/ work done so far:
desoldered CPU and installed a socket,
built up shifter board
built up dual tos board
recapped all motherboard electrolytics

20240830_182122.jpg

[rubber_jonnie]

Hey Bob - :welcomewave:

Just a quick one, we don't allow off site images here, so the one you've linked to does not show correctly. Can you please upload the image as an attachment (The tab below the text box) and then place it in-line using the button on the attachment list, thanks.

Given your onboard RAM is installed but disabled, you don't need to enable it again IIRC, you simply need to add the Shifter and MMU adapters, correctly oriented, and join with the cable.

However, more specifically with the MMU adapter, I'd strongly suggest you remove the mainboard and place it no a flat surface, probably on a thick piece of card or corrugated card, as the MMU adapter can require a lot of force to push in and it needs to have about a 2mm gap between the adapter and the socket when properly inserted.

You will cause the board a lot of flex and possibly damage it if you do it with the board in the case with inadequate support.

I know it's a lot of work removing the board, but so is fixing one that's been damaged due to board flex.

[frank.lukas]

Contact Lynxman for this Ram Upgrade at Atari-home.de or Atari-forum.com ...

dil_ausgelötet.jpg

eingebaut_dil.jpg

[RB80atari]

Hey Bob - :welcomewave:

Just a quick one, we don't allow off site images here, so the one you've linked to does not show correctly. Can you please upload the image as an attachment (The tab below the text box) and then place it in-line using the button on the attachment list, thanks.

Given your onboard RAM is installed but disabled, you don't need to enable it again IIRC, you simply need to add the Shifter and MMU adapters, correctly oriented, and join with the cable.

However, more specifically with the MMU adapter, I'd strongly suggest you remove the mainboard and place it no a flat surface, probably on a thick piece of card or corrugated card, as the MMU adapter can require a lot of force to push in and it needs to have about a 2mm gap between the adapter and the socket when properly inserted.

You will cause the board a lot of flex and possibly damage it if you do it with the board in the case with inadequate support.

I know it's a lot of work removing the board, but so is fixing one that's been damaged due to board flex.

Hi there,

Thanks for the welcome.
Sorry about the picture link, i have reuploaded the picture as an attachment, hopefully that works ok now.
By the way, i seem to be running into a problem when i post messages to the forum saying that my posts need to be validated or approved, is it possible for me to sort this out so i can just post freely?

Many thanks for the info about the ram install, great so i can leave the ram on the board as-is, that means one less thing to do. Maybe ill remove them all later if the new ram install goes ok...
But for now i just want to see if the machine will work.

The original power supply had failed when i bought it, so i havent had it up and running yet.
I have a meanwell rt-50A that im going to install and then i can try the machine, with hindsight i should have perhaps not recapped the board before trying the motherboard, but the recap went very well, nice and clean and so it should only be a good thing.
But i will remove the dual TOS board and the new cpu and booster board, ill try the machine with the old roms and cpu but with the new ram upgrade, then if working ok, ill add the dual tos board and decoder/booster later.

Great suggestion about laying the motherboard on some cardboard whilst inserting the MMU, i will do that...

I got somethings i got to take care of today, but tomorrow i will install the new Meanwell and power up the board for the first time, touch wood, fingers crossed it will work!

Cheers,
Bob

[RB80atari]

Hi Frank,

Thanks for the suggestion.
But i already bought the mmu ram upgrade board from Exxos, so i will use that.

But that upgrade does looks quite neat, i guess its probably more reliable to do it that way than piggy back into the MMU socket as well?
Might be worth ordering one. Whats the price?
I set up an account on Atari-forum.com as well, but i didnt see a thread about this ram upgrade?
Is it possible to send me a direct link so i can have a look please?

Cheers,
Bob

Contact Lynxman for this Ram Upgrade at Atari-home.de or Atari-forum.com ...


dil_ausgelötet.jpg


eingebaut_dil.jpg

[rubber_jonnie]

Hi there,

By the way, i seem to be running into a problem when i post messages to the forum saying that my posts need to be validated or approved, is it possible for me to sort this out so i can just post freely?

Cheers,
Bob

I've removed you from newly registered, you should be able to post freely now, but there are restrictions when you first come on line so we can be sure you're genuine and not just posting ads for weird stuff :)

[RB80atari]

I've removed you from newly registered, you should be able to post freely now, but there are restrictions when you first come on line so we can be sure you're genuine and not just posting ads for weird stuff :)

Thanks! :D