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The 245s are controlling the direction of the data flow to/from the data bus. I imagine making sure that the chip select is highly controlled might work, but for SRAMs that also signals the low-power mode for the chip.

Basically, there's nothing there which can select it. The 245s are straight through connections as are most of the address lines (via inverters). Given that I think only the address decode part of the chip is fried I'm looking at only replacing that for the time being, using a 74HC154. This...

OK, here's the final pin-out of the VLSI chip. The two 74AC245 buffers gate the data between the memory and the system memory data bus. The two 74AC240 chips invert the addresses A1-A15 and pass them to A0-A14 on the chips. SYS_POWER* is also inverted and passed back to the VLSI chip. The...

The initial checks of the two 74AC240s shows that they're being used purely as inverters for address lines A1-A15 and these are being passed on to the SRAM chips' A0-A14. _OE1 and _OE2 on both chips are tied to ground. G9's I7 (pin 11) is being used to invert the SYS_PWR* line and feed it...

Well spotted. As it turns out one of the two mystery pins was A16 but the other was connected to pin 9 (O7) of the 74AC240 (G9), which has the input of pin 11 (I7), which is connected to SYS_POWER* (and hence the next pin to the left).

Yay! I've found the last RAM_CS* line! Boo! I miscounted some pins and obviously bridged two of them iring testing. Yay! I'm down to two mystery pins! :-)

Thanks, that's what I thought, so for the address decode a 74LS240, an and-gate or two and a 74HC154 4 bit address demultiplexer would cover most of it. I've got a bit further today. I'm down to 6 pins I can't find the connections to, one of which should be the missing CS* line. All the SRAM...

I've found all but one of the CS lines now.

OK, found some more of the pin assignments: I've also powered the board separately and checked the voltages. Most of the pins on the "top half" of the chip, other than Pin 1, are at Vcc voltage whether or not A21 is high or not In fact nothing seems to change. None of the chip select lines...

With regards to chip select replacement I'm pretty sure that a 74HC154 would do the trick, if I could find all the *CS lines. A22 and A23 could go through diodes and then both connect to the *E1 pin on the 154. A21 would go through an inverter to *E2. This would enable the output on the chip...

This is how far I've got so far with the pin-out for the VLSI chip.

I've been buzzing out some of the connections. So far I've found the connections to A17-A23, LDS, VCC and GND on the input. So far, six output to pairs of CS- lines to the SRAM and the line to pin 11 (input 7) of the 74AC240 on the other side of the card. I'm guessing that I could replicate...

Try resetting using the debug and reset buttons at the same time. My non-backlit machine shows similar patterns when first powered up as it starts in an inconsistent state and crashes.

P.S. Just checked with all the SE/30 images on-line. No, it's not any of the chips on the SE/30. The closest part number is the Glue, but that's the wrong size and obviously designed before this chip as it's model number is smaller.

I've no idea I'm afraid.

A couple of months back I bought a 1MB SRAM card for my Macintosh Portable (non-backlight) from a vendor in France via eBay. Unfortunately the vendor lied that it was in full working order as it didn't work. (Thankfully I got my money refunded and he didn't want it back.) Well, something...