Performa 600 Cache Mod, IIvx pictures needed.

[GiGaBiTe]

I'm finally getting around to adding motherboard L2 cache to my Performa 600, as I found all of the required cache chips (SRAMs and TAG SRAMs) for a reasonable cost from a nearby surplus store.

The cache chips installed with no major issues, but they don't work, and I'm fairly sure it's because I don't have the resistor strapping right. There was a recent video on Youtube of a guy moving the cache chips, plus the resistors and capacitors from a donor IIvx motherboard, and it worked for him. The problem is that I don't have a donor IIvx motherboard, I just have kits of various value resistors and don't know the correct ones to use.

I found a grainy picture of the area on a IIvx motherboard, but I can't make out the markings on the resistors to know their values. I guessed some of the values and tried anyway, but it didn't work, Macbench doesn't show any performance difference. According to the Youtube video, there should be a 5-10% performance uplift with the cache enabled.

Here is the grainy image I found, with what my board currently looks like below it.

If someone with a IIvx could take a clear high resolution picture of the underside of the logic board under the cache area, it would be greatly appreciated.

 

[Fizzbinn]

Here you go!

 

[GiGaBiTe]

Thanks for the quick response!

It looks like my guesses were 99% correct for the resistor strapping based on the grainy picture from before. The only resistor I seem to have gotten wrong is R123. I put a 1k, where it should have been 100R. I corrected that, but I'm still not seeing any performance change.

The cache chips and the cache controller ASICs are getting warm, like they're being used, but I can't see any change. Before the cache chips and passive components were installed, the cache control ASICs would remain stone cold. If the cache is working, but something was wrong with it, I'm pretty sure I'd see a crash real quick when DMA is being used.

There are also some other resistor strapping positions near the cache area, but I'm not sure what they do. R129 and R130 suspiciously look like they deal with high frequency clock signals, because both of the the traces are surrounded on all sides with a ground trace. I wonder if this has to do with the clock doubling of the CPU? Someone would need to show a picture of a IIvi to know for sure.

R141, R143 and R144 is also strapping for something also possibly related to the cache due to its close proximity, but none of the positions are used on either the IIvx or Performa 600.

But here are all of the component values that are known, just to aggregate it into a single place. It'll help not having to scour the entire internet to figure it out again. If anyone has any ideas what I might be able to do to make the cache do something, it'd be appreciated.

Passives on the back of the board, these are all 0805 sized parts:

R123 - 100 Ohm (101)
R124 - 1k Ohm (102)
R125 - 330 Ohm (331)
R136 - 1k Ohm (102)
R140 - 1k Ohm (102)

C130 - 100 nF (A5 / 104)
C137 - 100 nF (A5 / 104)
C143 - 100 nF (A5 / 104)
C149 - 100 nF (A5 / 104)
C155 - 100 nF (A5 / 104)
C162 - 100 nF (A5 / 104)

Top of the board:

These are the cache controller ICs, I believe. Some motherboards shipped with these not installed. Pretty sure the cache won't work without these.

U53 - Apple 341S0901-A 242MM1A (Control 1)
U49 - Apple TI1684-5 23501SWXF 341S0879 (Control 2)

These are the SRAMs I used. I have seen various IIvx motherboards with speeds ranging from 15-25ns. With the bus speed being 16 MHz, it should be fine to use 25ns parts. I've even seen mismatched SRAM and TAG SRAM speeds on the same motherboard.

SRAMs (8kx8)
U47 - Cypress CY7C185-15VC
U48 - Cypress CY7C185-15VC
U50 - Cypress CY7C185-15VC
U54 - Cypress CY7C185-15VC

TAG SRAMs
U42 - AT&T ATT7C174J-15
U45 - AT&T ATT7C174J-15

 

[David Cook]

Using TechTool or a similar utility, what machine ID does your computer now think it is? The IIvi, IIvx, and IIvm/Performa 600 all have different IDs and thus might be executing different ROM/OS code to enable the cache.

 

[GiGaBiTe]

MacTest Pro shows:

Macintosh (ID = 45)
Macintosh IIvm
Performa 600

I'm guessing that I can't use something like "I wish I were" to smurf the Gestalt ID.

 

[David Cook]

I notice R146 is different between the two board images. It exists on yours but not on @Fizzbinn's board.

 

[GiGaBiTe]

Good find. I'll try moving it off one of the pads to take it out of circuit either later tonight or tomorrow and see if anything changes.

Might also go on a side quest and probe R129/R130 and see if that's related to some sort of high speed clock signal.

 

[David Cook]

Also noteworthy, the IIvx using a different system enabler than the Performa 600. Make sure you have both enabler 001 and enabler 304.

https://www.macintoshrepository.org/505-macintosh-system-enablers

So, if the cache is being enabled in that code (likely), it is critical that the System software believes your machine is a IIvx. Might be worth trying "I wish I were" if you can't get resistor changes to trigger it.