Migrating memory chips from 5400 board to 5500 board?

[pizzigri]

Hi everyone,
I was wondering, since I have both, if it could be possible or feasible to remove with a hot air station the 8MB DRAM chips of a 5400 logic board to solder them onto the pads of a 5500 board - or, removing the chips from an old memory stick (in this case, which SIMM/DIMM should I look for?), and if this would work without doing weird things to ROM etc.
Are there caveats? Resistors to move around on the board? Make no sense having 8MB additional ram on an already 128MB equipped Mac?


Cheers,
Franco

 

[macuserman]

This seems doable to me, but I've never tried to do it. I'm not sure the effort would be worth it though 8MB isn't really enough to change anything other than I suppose just to say you've done it.

 

[pizzigri]

Ah ok... it was just for bragging rights really...

 

[waynestewart]

I recall reading about someone doing that maybe a dozen years ago. They reported success

 

[Fizzbinn]

I think it would be more of a "because its cool, a challenge, and/or fun" thing. Also some clone vendors have 16MB on their boards based on this architecture so that might be possible too with the right chips...

On another forum's Discord chat someone recently posted about doing this on their 6500 and it seemed to work, although not sure where they got their donor chips from.

One thing to consider is if RAM chips to add on the 5500 should be regular FPM or EDO. I think the apple 54/6400 service guide points out how to tell what type is on the logic board. If you have EDO on board I think there is supposed to be some benefit to using EDO DIMMs.

 

[croissantking]

Why not go the whole hog and use bodge wires to get another 128MB on there, similar to how someone did with an LCIII to get to 64MB? Are there enough RAS/CAS lines?

 

[trag]

IIRC, there are four positions for the memory chips. The trick is that the chips are 16 bits wide and 16 bit wide RAM chips are fairly rare. The other fun bit is that they're in an SOJ package (SOJ-42?). So when hunting for these FPM chips, search for that. I've seen some old 168 pin FPM DIMMs built with these chips.

I think this is an example: https://www.ebay.com/itm/371692842921

These are 1M X 16 so four of them will give you 2MBytes X 4 = 8 MB of capacity. It would be nice to find much denser nM X 16 chips.

 

[pizzigri]

Well, the point is to add memory, and since I have a 5400LB, it would make sense to get the chips from that board up to 8MB... cheaper - actually free- as I already have the board. But if 16 or even 32MB can be added to the 55-6500 board that would be, well, cool.

 

[pizzigri]

What about these? They are on a 72pin ram, I believe 8mb, there are four chips two per side.

 

[MacJunky]

This seems doable to me, but I've never tried to do it. I'm not sure the effort would be worth it though 8MB isn't really enough to change anything other than I suppose just to say you've done it.

To say that you have done it, and cause future headaches down the road when the chips you added start failing. Also to do it on the slowest board in the lineup you have access to, so that you further waste the effort on something that can barely run the software it was bundled with in the first place even if it has maxed RAM and a Radeon 7000. Lets not forget the ability to crash run as many programs as possible with Virtual Memory disabled too. And to confuse anyone who dares look at Apple System Profiler.

On another forum's Discord chat someone recently posted about doing this on their 6500 and it seemed to work, although not sure where they got their donor chips from.

As seen below 8MB is bootable with a minimal enough operating system, but 8MB alone is not terribly useful for this particular PPC on a regular basis. Mac OS 8.6 still uses 11MB with extensions disabled, for example. I have not tested with 7.5.5 or 7.6.1.
The 6500 detects a correct total of 136MB, but incorrectly displays the quantity of memory in it's various slots. When it should see 8/64/64 and be able to identify slot numbers, it sees 16/64/32 and can't identify the slot numbers. As far as I can tell all memory is usable if the tests in Mac Test Pro, Tech Tool Pro, and GaugePro are anything to go by.

At the end of the day it is still neat and I do not regret it. If anyone has any more ideas about further expending the RAM, this board seems to be a guinea pig for such antics. Perhaps some day it can be replaced with a faster model or receive a cache slot G3 upgrade, or be replaced with a faster and more upgrade-able system altogether.

 

[pizzigri]

Well, it seems the ram stick i have uses the exact same chips, that Macjunky used. So I actually may try to move the chips on the 6500 board and see what happens. I cant understand why it would give so many problems tho, I would have imagined that since the pads are there, it was supported. silly me.....

 

[MacJunky]

It would be neat if some of the firmware gurus around were able to figure out the whats whys and hows related to the extra RAM.

Beyond that, if you are curious to try it then by all means add the RAM to your board!
I would imagine there are not too many 6500/5500 boards in this world with 136MB RAM, though the jury is still out if we will be judged for cannibalizing working vintage RAM sticks to heinously ruin perfectly good working pristine virgin Macs!(ohno! hahaha)