4Mb MMU Socket Upgrade questions

[exxos]

It could be the PSU is failing if its not been recapped. Though indeed its better to take the old RAM out anyway. Some people did report issues until they removed the old RAM. It is difficult to diagnose because faults can be in multiple places.

Also assume you lifted the "MMU side" of the resistors (next to the R91 text etc) and connected the free end of the resistors to 5V ?

[Trip3nite]

It could be the PSU is failing if its not been recapped. Though indeed its better to take the old RAM out anyway. Some people did report issues until they removed the old RAM. It is difficult to diagnose because faults can be in multiple places.

Also assume you lifted the "MMU side" of th resistors (next to the R91 text etc) and connected the free end of the resistors to 5V ?

Tested with both a new and an old psu so that shouldn't be the problem.
And yes the right side of the 68R resistors are lifted connected to 5v (checked for continuity to be safe, all good)
I was thinking I could first put it back to stock and see if things work again so then I know whether my board is still ok.
Now that I think of it, would my system be able to boot as normal if i just remove the ribbon cable and shifter board and put the shifter back in its socket, reconnect the resistors, but leave the upgrade board for the MMU socket where it is?
As long as I'm making good connection with the pins and mmu I should be able to boot right?
If that's the case, and it boots, I'm at least sure I'm making good connection with the mmu so I can rule that out as a problem.
Or can leaving the mmu board seated be a problem for either my sytem or the mmu board itself?

[exxos]

I was thinking I could first put it back to stock and see if things work again so then I know whether my board is still ok.

Always a useful thing to do.

Now that I think of it, would my system be able to boot as normal if i just remove the ribbon cable and shifter board and put the shifter back in its socket, reconnect the resistors, but leave the upgrade board for the MMU socket where it is?

Not really sure on that one to be honest never really thought about it or tried it. But I would recommend removing the MMU board and not leaving it in while trying to power up old RAM. The MMU simply might not be able to drive two banks of RAM which could be the problem people generally seem to run into. So even with the data bus disconnected from the 4MB board, you could still actually have the same problem anyway.

As long as I'm making good connection with the pins and mmu I should be able to boot right?

Not sure in what context you are asking the question for.. As said above I would not recommend leaving the MMU 4MB board in place while trying to diagnose MB faults.

If that's the case, and it boots, I'm at least sure I'm making good connection with the mmu so I can rule that out as a problem.
Or can leaving the mmu board seated be a problem for either my system or the mmu board itself?

Again I cannot say I have not tried that or diagnosed any potential issues in doing so. Personally I think it's a bad idea trying to power a RAM board up with half its signals missing.

I really would suggest just taking your machine back to stock. Making sure it still works. Then completely removing the old RAM and refit the 4MB board. If it still does not work, then you have a bad connection somewhere, bad solder joint, or a bent pin etc somewhere. Some people do manage to insert the board in the wrong orientation which could likely damage the board.

[Trip3nite]

I really would suggest just taking your machine back to stock. Making sure it still works. Then completely removing the old RAM and refit the 4MB board. If it still does not work, then you have a bad connection somewhere, but solder joint, or a bent pin etc somewhere. Some people do manage to insert the board in the wrong orientation which could likely damage the board.

I just put it back to stock and everything works again.
One weird thing my machine does have is that my screen jitters after startup until it stabilises after a few minutes, which was already the case before I did the upgrade.
Idk what causes this or whether its relevant to the problem I'm having with the upgrade, but I thought I'd mention it
I'm pretty convinced the ram isolation was correctly done as instructed.
Can I assume that the mmu board was probably making good connection as well, as there was just a bunch of extra pins jammed into the mmu socket and it still worked just fine after removing it?

I wanna make sure that before I go and desolder all those ram chips from my as of now still working system, the problem isnt with some part of the upgrade itself.
I checked for shorts and continuity, and otherwise I don't see anything suspicious on the boards.
If the problem is with the upgrade, I think it might just be that I used too much pressure when pushing it into the mmu socket...
I suppose there's no easy way to check whether the ram upgrade is still working fine?

[exxos]

I just put it back to stock and everything works again.

:thumbup:

Can I assume that the mmu board was probably making good connection as well, as there was just a bunch of extra pins jammed into the mmu socket and it still worked just fine after removing it?

I don't think it can be assumed no. I generally recommend just wiping the pins with some IPA to make sure, it's all that really can be done. I have never known anyone have any contact problems after wiping with IPA.

I wanna make sure that before I go and desolder all those ram chips from my as of now still working system, the problem isnt with some part of the upgrade itself.

It is difficult to know, did you assemble the shifter board yourself ? A lot of people struggle with soldering the board themselves.

Have you doubly checked you don't have any bent pins on the RAM board while inserting into MMU socket ?

Checked you correctly matched pin1 on the MMU board to pin 1 on the MMU socket ?

If the problem is with the upgrade, I think it might just be that I used too much pressure when pushing it into the mmu socket...

If you are thinking you broke it by inserting it, you would really be the first if that was the case. The only people who manage to break it that I am aware of, inserted incorrectly (did not align pin one) and kill the board. Beyond that it is generally users soldering which is at fault. Beyond that removing the existing RAM chips also helps a lot. Beyond that I really don't know what to suggest because it is not a problem I have seen before. But indeed people have fitted the upgrade to those specific motherboards lots of times anyway.

I suppose there's no easy way to check whether the ram upgrade is still working fine?

Not without sending it back to me to verify it works in my test machine. They are all tested out before I ship them anyway.

[Trip3nite]

It is difficult to know, did you assemble the shifter board yourself ? A lot of people struggle with soldering the board themselves.

Have you doubly checked you don't have any bent pins on the RAM board while inserting into MMU socket ?

Checked you correctly matched pin1 on the MMU board to pin 1 on the MMU socket ?

If you are thinking you broke it by inserting it, you would really be the first if that was the case. The only people who manage to break it that I am aware of, inserted incorrectly (did not align pin one) and kill the board. Beyond that it is generally users soldering which is at fault. Beyond that removing the existing RAM chips also helps a lot. Beyond that I really don't know what to suggest because it is not a problem I have seen before. But indeed people have fitted the upgrade to those specific motherboards lots of times anyway.

I soldered the socket and pins to the shifter board myself, and it looks fine.
The ribbon cable connector and cap came already pre-soldered to the board.
I checked for shorts and continuity on the shifter board, and i suppose I can also check the cap and check continuity from the socket to the other end of the ribbon cable if I wanna be really sure the shifter board is ok.

I did check whether I oriented the mmu board correctly, which is the same as how I've seen it fitted in all photo's of systems with my board revision.

I guess the only easy thing I can still try is clean the mmu but i dont have a tool small enough to pull it out, and I don't wanna try to get it out with something else.
So I guess I'm gonna go get one of those tools and try to clean it, but something tells me this won't be it.
Maybe I should just desolder the ram, as I have to do that sooner or later...

Thanks for the help anyway!

[exxos]

Maybe I should just desolder the ram, as I have to do that sooner or later...

You can just cut them out.

I did explain a bit on that in this video.





Think you said you tried it on another board ? If so which one ?

Also , have you got the ribbon cable the right way ? (can just make out the silver top connectors on the cable)

Capture.PNG

Always useful to post images how you fitted everything.

[Cosmic Puppet]

I have the exact same revision board. I upgraded to a Marpet 4MB and it was R90 and R91

20190711_133934.jpg

Hey there!
Sorry for digging up this old topic but I also have a motherboard with less resistors like this one, only mine is a 1040 instead of a 520.
Could this change which resistors I need to lift and tie to 5V, or would it also be R90 and R91?

Thanks!

Hi there. Sorry I missed this. Glad you have found the help you needed.