4Mb MMU Socket Upgrade questions

Upgrade your RAM from ST to Falcon.
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Cosmic Puppet
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Re: 4Mb MMU Socket Upgrade questions

Post by Cosmic Puppet »

I have the exact same revision board. I upgraded to a Marpet 4MB and it was R90 and R91
20190711_133934.jpg
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polbit
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Re: 4Mb MMU Socket Upgrade questions

Post by polbit »

Cosmic Puppet wrote: Sat Sep 12, 2020 1:27 pm I have the exact same revision board. I upgraded to a Marpet 4MB and it was R90 and R91
Thanks!
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Re: 4Mb MMU Socket Upgrade questions

Post by Cosmic Puppet »

polbit wrote: Sat Sep 12, 2020 1:39 pm
Cosmic Puppet wrote: Sat Sep 12, 2020 1:27 pm I have the exact same revision board. I upgraded to a Marpet 4MB and it was R90 and R91
Thanks!
No worries. Can't believe someone has the exact revision as me. :lol:
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polbit
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Re: 4Mb MMU Socket Upgrade questions

Post by polbit »

OK, I give up. Second motherboard I've tried to install the memory upgrade on, and all I get is black screen. I got the two 68R resistors to 5V on left side of the big capacitor, checked continuity on all the shifter pins and the cable, made sure everything was positioned correctly, but I get nothing.
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Re: 4Mb MMU Socket Upgrade questions

Post by exxos »

I suggest you get someone like @Steve to look at this for you. Its possible it needs the bus resistors updating or some other problem with connections or something.
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Re: 4Mb MMU Socket Upgrade questions

Post by megalith »

I installed everything per instructions.
I went through the board to find the 68ohm resisters.

In my case: R90, R93, R94, and R91 were all 68ohms.
I lifted the right side, and bridged them to a wire I rant to +5VDC
I used the positive side of C88 because it was super close to the resisters.

In the 4MB position, I get 4 bombs and an insufficient memory message.
In the 1MB position, I get a black screen.

For sanity sake, I removed the upgrade, reconnected the resisters, and removed the power connector from C88.
Turn the machine back on, and everything is fine. With 512K :)

Attached below are pics of my motherboard from various distance and sections.
You can see the shiny solder on C88 when i pulled my 5VDC from, as well as blobs of solder on the labeled side of the resisters that i cut and attached to power.

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unnamed (2).jpg
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Re: 4Mb MMU Socket Upgrade questions

Post by exxos »

Sounds like you have a bad connection somewhere. Wipe the pins on the ram board with IPA. Mostly problems are bad soldering on the shifter adapter.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Trip3nite
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Re: 4Mb MMU Socket Upgrade questions

Post by Trip3nite »

Cosmic Puppet wrote: Sat Sep 12, 2020 1:27 pm 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!
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Re: 4Mb MMU Socket Upgrade questions

Post by exxos »

It be easier / Quicker just to lift all 4 than to try and figure out exactly which ones to do.

With so many motherboard revisions and changes in resistor numbering.. it's why I never quote them as it makes things more confusing than just just lift the bank of 68R and have done with it.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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People should find solutions to problems, not find problems with solutions.
Trip3nite
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Re: 4Mb MMU Socket Upgrade questions

Post by Trip3nite »

Epic, I seem to have ran into the same problem! :D
Followed all instructions, and when I power on I get a black screen (no border, and a constant beep coming from monitor 2sec after powering on)
My board is also a silly style C070523 type, rev. D, but it's a 1040stf instead of 520stf.
I know these old boards can be a bit fragile so I was super careful during the whole process.
I've triple checked everything for continuity and shorts, including the ribbon cable, I checked if the 4 resistors I lifted still had correct values.
I even checked for continuity and shorts with the pins of the mmu socket on the under side of the motherboard to the ones on top of the mmu upgrade board.
No chips get hot when it's powered on, but I never left it powered on for longer than maybe 10sec because I was afraid something bad might happen.
Also, I'm using a new psu, but tried stock psu too and the same thing happens.
Can a bad contact with the mmu/upgrade board pins cause this kind of problem with a black screen?
I did see a post about slightly bending the pins of the mmu to ensure better contact, but I thought I'd check here first, maybe there's something more obvious I could try first, and I dont wanna mess up bending such small pins...
Otherwise I have no idea what could have gone wrong.

PS.
When I was looking for info on exactly which resistors to lift, I did come across posts by some other people saying their system didn't work after a ram upgrade, but after removing all ram chips from the board instead of disabling ram with the resistors, they did get it to boot.
Can't seem to find those post though, so maybe I remember wrong, or maybe they did something wrong when trying to disable ram...
Could removing the ram chips maybe also work for me, or can I be pretty sure something went wrong already?

(tell me if this should be its own topic)
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