Old GFX Cards and their Lego Brick RAM

Arkious · Oct 29, 2013

Hi All,

I have a question regarding the GFX cards used in older Macs, specifically that in the iMac G3 DV (Rage 128 Pro).

I have overclocked the iMac CPU by 100MHz to 700MHz already and have a software overclock on the GFX card. But i was wondering if anyone has or would know if it would be possible to upgrade the GFX card RAM. I see there are plenty of Rage 128 Pro/Ultra 32MB GFX cards kicking around for very cheap, so was wondering if swapping out the RAM chips would work.

I am skilled with soldering so i have no worries there other than it not working or damaging both sets of RAM in the process.

Please let me know if anyone has tried or knows anything about this as i wasnt sure if it would work that i would need different firmware in order to utilise the RAM.

Thanks

666sheep · Oct 30, 2013

Never tried that, but there's certainly one limitation: ROM of the video card. It has fixed memory size.

Arkious · Oct 30, 2013

Yeah I understand I couldn't simply put 64MB or 128MB onto it. But because they came with 8,16 or 32MB variants I thought maybe it's possible could buy a 32MB card, unsolder it's chips and switch them with those on the iMac Logic Board.

Do you think it's feasible? I am not sure how the Rage 128 is mounted, but if it does work switching the RAM it may be worth switching a pro for an ultra too

rabidz7 · Oct 30, 2013

Arkious said:
Do you think it's feasible?

Only if you flash the card to the 32MB version.

Arkious · Oct 30, 2013

Yeah that was my worry, I suppose that is almost impossible to do

666sheep · Oct 30, 2013

It's most likely possible at least in 2 ways:
– Graphiccelerator - it's able to dump the ROM from iMac's onboard EEPROM, so it theoretically would be able to flash it with modified ROM
– standalone programmer - requires ofc desoldering and soldering EEPROM back after flash
I'd start with regular (AGP or PCI) Mac ATI Rage and G4 (if you have one by the hand) and if you'd succeed then replicate whole procedure on iMac.

Mac Rage ROM could be modified to recognize more memory. You'd need to do some reading on themacelite and track in various PC ATI Rage BIOSes where RAM amount offsets are located. Memory timings and clocks could need to be modified as well. RaBiT should help you in this. It will be a long trial and error battle, but reward could be worth it

No one has done this before AFAIK.

Arkious · Oct 30, 2013

Well, this does sound tempting!

I have my eyes on this as it's round the corner from me and only a few £ on eBay.

http://bit.ly/1aoLtFx

I have no worries soldering the chips but modifying the EPROM I have no idea.

666sheep · Oct 30, 2013

You need to modify ROM (aka BIOS, i.e. content of EEPROM) file, not the EEPROM itself.

Arkious · Oct 30, 2013

666sheep said:
You need to modify ROM (aka BIOS, i.e. content of EEPROM) file, not the EEPROM itself.

This will be interesting! say i do switch the RAM chips... it should work as normal but only utilise 16mb of the 32mb correct?

at least that way i will be able to tell if the RAM is working to start with

Arkious · Oct 30, 2013

Arkious said:
This will be interesting! say i do switch the RAM chips... it should work as normal but only utilise 16mb of the 32mb correct?

at least that way i will be able to tell if the RAM is working to start with

Had the board out and can only find 2 RAM chips. the actual graphics cards on the likes of ebay have more, so maybe this is unachievable?

666sheep, i remember speaking with you a while back about overclocking the G3, which i did following your advice. You said you could do a volt mod to the GPU, but couldnt remember how you did it. did you ever find out how to do it again?

also another thing... i see apple states that the iMac G3 can only run 512MB but it can actually run 1GB... but is this because there was only availability of 512MB sticks of RAM? as i seen that there is non-ECC low density 1GB sticks of RAM available for a reasonable price. Has this been tried? 2GB would be nice xD

like this
http://www.ebay.co.uk/itm/Samsung-S...Memory_RAM_&hash=item46154011b7#ht_3640wt_730

666sheep · Oct 31, 2013

You should check specs of these memory chips and see if they're were manufactured in bigger size (density).

I was talking about CPU not the GPU voltage regulator IIRC. Didn't do anything with GPU in my iMac.

Regarding memory, I'm 100% positive that it won't work. I think that's hardware limitation (memory controller most likely, not sure here). PM G3 B&W, for instance, has 4 slots and only max 1GB RAM. Doesn't even recognize 512MB sticks.

Arkious · Oct 31, 2013

666sheep said:
You should check specs of these memory chips and see if they're were manufactured in bigger size (density).

I was talking about CPU not the GPU voltage regulator IIRC. Didn't do anything with GPU in my iMac.

Regarding memory, I'm 100% positive that it won't work. I think that's hardware limitation (memory controller most likely, not sure here). PM G3 B&W, for instance, has 4 slots and only max 1GB RAM. Doesn't even recognize 512MB sticks.

Ahh ok, if u can remember the voltage mod that would also be useful

I will research the memory, it will probably be difficult to find the memory nowadays! But still I will have a look.

It's a shame about the RAM :-(

Arkious · Oct 31, 2013

666sheep said:
You should check specs of these memory chips and see if they're were manufactured in bigger size (density).

I was talking about CPU not the GPU voltage regulator IIRC. Didn't do anything with GPU in my iMac.

Regarding memory, I'm 100% positive that it won't work. I think that's hardware limitation (memory controller most likely, not sure here). PM G3 B&W, for instance, has 4 slots and only max 1GB RAM. Doesn't even recognize 512MB sticks.

found an interesting conversation regarding the Bus speed of the iMac G3.

http://translate.googleusercontent....&st=60&usg=ALkJrhg7ONZ2MD0P8yIL_I7mjN3IhcKy1Q

unfortunatly it never does say if he went ahead and tried it :-(

I will however be taking mine apart to see if i can find these resistors, 133 would be quite amazing however i cant see it working

This is a fantastic site offering information for all PPC G3-G5 overclocking (in french but google translate each bit you wish to read)

https://sites.google.com/site/overclockmac/

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