exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 27 Jan 2025 10:42 I'd second what @exxos said about repeatedly pushing on the MMU adapter, it's certainly feasible that the fine pitch pins now have bad joints from pushing in and out multiple times, and I have even once bent a pin on one of these. It went on to be fine but it is tricky.

What you're seeing is definitely a memory issue, but by the same token it is likely to be a connection issue.

Also, can you add a picture of the fitted adapter showing how far it is inserted into the socket and how you've disabled the original RAM.

I would add that I know these are tested before being sent out and I have fitted quite a few with no issues.

Thanks for the reply.
What you say makes sense and agree.
Will try a new ribbon, it does have a crimp in it from folding. Would love for this to be the issue, but wouldn't be surprised if that is not the problem.
It was working fine until I put the keyboard on top & top shell, moving the Ribbon cable. Would take off the keyboard(gently press around top of the mod) , and would work again. Rinse repeat 15x
Now does not work all.

Will update.

Attaching picture

WilsonB wrote: 28 Jan 2025 04:56

rubber_jonnie wrote: 27 Jan 2025 10:42 I'd second what @exxos said about repeatedly pushing on the MMU adapter, it's certainly feasible that the fine pitch pins now have bad joints from pushing in and out multiple times, and I have even once bent a pin on one of these. It went on to be fine but it is tricky.

What you're seeing is definitely a memory issue, but by the same token it is likely to be a connection issue.

Also, can you add a picture of the fitted adapter showing how far it is inserted into the socket and how you've disabled the original RAM.

I would add that I know these are tested before being sent out and I have fitted quite a few with no issues.

Thanks for the reply.
What you say makes sense and agree.
Will try a new ribbon, it does have a crimp in it from folding. Would love for this to be the issue, but wouldn't be surprised if that is not the problem.
It was working fine until I put the keyboard on top & top shell, moving the Ribbon cable. Would take off the keyboard(gently press around top of the mod) , and would work again. Rinse repeat 15x
Now does not work all.

Will update.

Attaching picture
474845523_952662807002010_3847253137480930701_n.jpg

It looks to be inserted OK, so that's a good start and a replacement cable may help. Can you also show us how you've disabled the old memory? Did you tie resistors to 5v or did you remove the old RAM entirely?

This upgrade doesn't expand the RAM, it replaces it so it is important the old RAM is either removed or disabled. Given you've said it works fine without the adapter fitted, that suggests you still have the old RAM running.

I recieved a dozen ribbon cables.. They are exact.. Unfortunately still no joy..

What's the next step?

I suggest continuity checking from the shifter data pins to the mmu adapter ribbon connector on the PCB.

I also don't believe you posted an image of how you disabled your old ram. But that's a method I do not recommend anymore as people have reported problems until the old ram was removed.

My only other thought is as was mentioned before repeated pushing on the board has weakened a solder joint on the pins. Or if considrable force was used, it could have bent the PCB breaking a solder joint anywhere on the mmu adapter. In which case you would have to continuity check the used pins connect to the ram ics and the ribbon connector connects to pins on the ICs. I can post the PCB layout if it helps. But I'd start with ras cas lines from the mmu pins to the ICs on the mmu adapter itself.

EDIT:
Another quick testing tip is to gently push down on one IC on the mmu adapter and power up your machine to see if anything changes. Repeat for the other IC and your machine has to to powered off for a few seconds between tests.

Also you can sometimes find pin contact issues by gently rotating the mmu adapter which will apply force on the pins to see if anything changes when you power on. You need to keep the force applied while powering up and not use excessive force else you risk bending and damaging the pins.

After many hours, Im running out of hope and it is down to the Exxos adapter.
I have soldering skills, so would rather make a perm 4mb upgrade.


Question for troubleshooting and your long experience,
The assumption is that if it fail boots as shown, it will stay like that until power off/back on. Meaning, If it is a specific contact and a connection is made, Atari prob. wouldn't recover live, a off / on is required. True?

I'm afraid I don't really understand what you are asking... Sounds more like you are having a reset issue now ?!

It is very difficult to help you when you haven't even yet posted a picture of how you have disabled the old RAM, or confirmed you have continuity check the shifter board etc.. You need to answer the questions and follow the advice in order to make the best progress but currently it is unclear if you have tried anything yet other than repeatedly pushing down on the board, which seems to have generated even more problems, and changing the cable which didn't help.

Maybe @coonsgm might be interested in diagnosing your machine for a video... ?

I disabled the onboard 1MB Ram by disconnecting the resisters and bringing them high.
This was going to be a temporary solution because of the adamancy of unsoldering all old ram on board.

As stated in the past, this Method WAS working with the EXXOS at 4MB that I purchased 3 months ago.
Fully tested for hours and successfully used setup for days, until reassembling keyboard/top case.

Again everything WAS working great, UNTIL the reassembly of the keyboard and case on top every time.
It was most likely the keyboard/case pressing down/moving the EXXOS daughter on top of MMU.
Even insulated the top of it to prevent any possibility of shorting with the bottom of the keyboard components.
So that wasn't the problem either, since it worked/then did not work again.
I even went through and tested out EACH pin on Daughter to the bottom of MB and all connections were good a few times.


After hours of troubleshooting, I now have it back to stock 1MB and working. No problems with the MMU socket, chip or any other components.

I am glad I DID NOT remove all original memory chips, else I would be in an even worse situation.

If you're in the US, I'd be happy to take a look at it and as Exxos says, maybe turn it into some YT content.

If you're interested shoot me an email or a PM