Performa 600 Cache?

[GiGaBiTe]

So I finally got motivated to tear apart my Performa 600 to repair it. It has the classic problem of leaky SMD caps, and some bad axials near the power connector (which I've replaced already.)

When I was washing the electrolyte off the motherboard, I came across these interesting unused solder pads:

If the markings are to be believed, it's supposed to be populated with some 8K x8 SRAMs, which looks like might be CPU cache. According to various internet sources, the Performa 600 (and IIvx) can't use a PDS cache card, but I'm wondering if it can have some cache soldered to these pads and be used.

Has anyone ever tried to solder on cache to a Mac motherboard before? If I can find some 28 pin SRAMs, I might try it. Though I'd solder sockets onto the pads first because I've not had good luck soldering memory chips and not have them burn up. If it's doable, I'll add it to my list of mods (adding a 68882 and overclocking the CPU to 40 MHz)

 

[NeXT]

You seem familiar. ;v

I do not see why the Mac would reject it unless it is disabled in ROM however it does not look too hard to add the simm slot for the ROM, patch an image and burn it to one of the available flash ROM Simms to make it all work.

 

[GiGaBiTe]

Well I guess I'll try it then.

The trouble now is finding the right SRAMs for it. It looks like the Mac IIvx uses the same motherboard design and has these chips installed. I'd love to see the part numbers on these chips, but unfortunately I can't seem to find a high enough resolution shot of the IIvx to see the markings.

From the crappy shots I've seen of the IIvx, the four 8kx8 SRAMs look like normal SRAMs, but the two TAGRAM chips look to be different parts.

 

[Unknown_K]

I think I have a IIvx board in my scrap heap (battery explosion) that I can check out later.

 

[Unknown_K]

SRAM 8Kx8: CY7C185-25VC 9251 15559Z
TAG: ATT7C174J-15 9250K 40

 

[GiGaBiTe]

Cool, thanks for the info.

I found some new-old stock of the 8kx8 SRAMs on Ebay, but the TAGRAM is proving more difficult to find.

 

[Unknown_K]

No idea if the machine will look for and use the cache if installed, let us know.

 

[GiGaBiTe]

So uh, you wouldn't happen to want to let go of that Mac IIvx motherboard for like shipping cost would you?

I've scoured the interweb and I can't find those TAGRAM chips or two other compatible chips listed in the datasheet. There's a diagram of the TAG circuit in those specialized SRAMs but I'm not versed enough in electronics to build it, especially since there's some unlabelled parts.

It'd also save me from having to buy a 40 MHz oscillator and some other parts.