Only 64MB RAM of 128MB recognized in PowerBook 3400

[chrisrueckert]

I have this module that I bought on ebay "tested and working" with 128MB RAM in a PB 3400. Does anyone know why it only shows 64MB?

 

[Fizzbinn]

Maybe its a 128MB module designed for the original PowerBook G3, pretty sure not all modules work the same between that machine and the PowerBook 3400 (its immediate predecessor) that otherwise use mechanically identical/compatible modules.

You can look at the hardware dev notes for both PowerBooks http://powerbook.micahgartman.com/ here. Looking at the one for the G3 it notes a bunch of compatibility weirdness.

 

[mdeverhart]

I think Fizzbinn is onto something here. Looking at the 3400 and G3 developer notes, there’s a memory controller difference for 128 MB cards (64 bits wide, 4x 4M x 16 Bit DRAMs per Bank, 4 banks):



The 3400 version of that configuration needs address bits 9 and 10 swapped on the memory card, while the G3 does not. Additionally, while I couldn’t find the exact datasheet for the DRAM chips on the card, a similar datasheet did show that these are 12 row bit / 10 column bit DRAMs.

So, seems like everything lines up to say that this card is probably for the original G3 instead of the 3400.

 

[MacUp72]

I dont have a 128MB module, but I think those have 4 chips on it..

 

[Phipli]

I dont have a 128MB module, but I think those have 4 chips on it..

View attachment 63393

That depends on the brand. They're just buffers, probably for level shifting.

 

[MacUp72]

hm, I wonder what modules actually are good candidates for upgrading up to max 128MB
So far I had three different ones, two were 16 MB and one 32 MB..
they didnt look alike, they used different platines and different sets of ICs and RAM chips.

backs look differently but NO one has chips on the back, just on the front.

16MB, fully populated but older RAM type, 28 pin, platine reads PB3400/32.
I also had two 16 MB ones with only four RAM chips on it.



32 MB, platine reads 3400/128 but only eight RAM chips (newer chip type 50 pin)
this is the one I hve currently in my 3400, though the printing says 3400/128MB theres only space for 16 chips and this maybe could be popuated to 64MB (but not 128MB)




these seem to be 64MB ones




then the alleged 128MB one with 4 controller chips instead of four, but these all have the newer chip type.



the platines seem to be just blanks with the basic model type they were produced for and even those were populated differently .

 

[MacUp72]

ok, I can confirm a 128MB RAM card can actually look like this, only 2 controller chips, instead of four, and no ram chips on the back.

 

[Phipli]

ok, I can confirm a 128MB RAM card can actually look like this, only 2 controller chips, instead of four, and no ram chips on the back.

As I said above, the 2 and 4 chips thing isn't to do with what computer the boards were designed to work in, it was just which parts the boards were built using - a design decision. Imagine moving the same amount of stuff using two small wheelbarrows or one big wheelbarrow.

They're also not controller chips, most of the chips you're looking at are buffer chips, the provide some isolation from one side to the other to help with driving downstream circuitry, sometimes also to allow you to connect chips with different voltages together.

 

[MacUp72]

ok, thanks, that clears some things

 

[Phipli]

32 MB, platine reads 3400/128 but only eight RAM chips (newer chip type 50 pin)
this is the one I hve currently in my 3400, though the printing says 3400/128MB theres only space for 16 chips and this maybe could be popuated to 64MB (but not 128MB)

This probably means that you could get 128 by replacing the existing RAM chips with higher capacity versions, and adding more of the same to the empty pad. Sometimes the difference between a 16MB and 32MB SIMM (or whatever) is just the RAM chips they fit to the same PCB.

 

[MacUp72]

maybe this would work when those exact EDO chips are available, you could butcher other RAMs of course, did this with the 540c.