Help to identify a vintage IC

[powermax]

Hi crews,

I'm trying to repair a vintage computer circuitry that contains an unknown IC in the DIP-8 package. It was used in several Macintosh computers around 1993/1994.

The IC in question is marked with the Apple logo and contains the following digits: '90 0120'. I attached a zoomed picture of the IC as well a schematic showing the related components.

The IC in question (U12) could be an ASIC. But it could be also a custom version of some other IC like the Cuda MCU (U17) which is just a custom version of the 68HC05.

The unknown IC (U12) is attached to a non-rechargeable 3.6V lithium battery. Its purpose is supposedly to manage the power source for U17 that implements a small nonvolatile RAM. U17 is therefore always powered either by the mains or the battery.

Any ideas on what it could be? Did you ever see anything like this?

Thank you in advance!

[R_J]

Re: Help to identify a vintage IC

I would guess its a Pram storage, similar to cmos time/date backup in a pc. S1 could be the clear "cmos" switch?
It might help if we knew which computer etc. it is used in.

[stj]

Re: Help to identify a vintage IC

looking at the schematic, it may be a serial sram.
probably because that mcu is a poor choice with no internal eeprom.

[powermax]

Re: Help to identify a vintage IC

Thank you for the interesting suggestions!

It might help if we knew which computer etc. it is used in.

I know for sure it's used at least in Macintosh Quadra 840av and PowerMac 6100.

looking at the schematic, it may be a serial sram.

Assuming it's a serial SRAM, what's your guess on the possible pin functions? From what I see in the schematic:

1 seems to be +5 V power source + that strange S1 switch
2 is connected to the trickle power (standby power) coming from the PSU
3 is connected to PC1 of the MCU (data line)
4 GND
5 not connected ?
6 is connected to PB0 of the MCU (another data line)
7 backup battery (3.6V lithium)
8 +5 V

probably because that mcu is a poor choice with no internal eeprom

Well, U17 was probably a custom model of 68HC05 that does include 4096 bytes of programmable internal ROM and 368 bytes of RAM.

[stj]

Re: Help to identify a vintage IC

1 reset
2 +5v standby
3 interface
4 0v
5 ??
6 interface
7 battery supply
8 +5v

[R_J]

Re: Help to identify a vintage IC

Max801 or max808, looks like pin 8 output connects to R120 and R83 and maybe elswhere? S1 is likely refered to as the cuda switch

[powermax]

Re: Help to identify a vintage IC

Max801 or max808

Yes, I agree that the unknown IC looks like a power supervisor thingy, similar to Max801/Max808 but not exactly. If I'm reading the schematics correctly, Cuda gets its power from our IC via pin 1, not 8. That's because Cuda's VDD is on pin 13.

Pin 8 of U12 seems to be connected to +5V of the logic board.

S1 is likely refered to as the cuda switch

Bingo!

[powermax]

Re: Help to identify a vintage IC

S1 is likely refered to as the cuda switch

Pressing S1 will short pin 1 to the ground and thus cut off Cuda's power efficiently resetting the latter. Right?

[R_J]

Re: Help to identify a vintage IC

U12 pin 1 seems to be connected to +5v (triangle with lines) Pin 2 via r112 (22Ω)to +5TRKL.
Without the complete schematic its hard to say where pin 8 (triangle) also goes other than where I mentioned

pin one +5v is not likely supply +5volts but a source with the (3line triangle)