IC identification help - Page 1
Forum section: electronics / repair

author: Maximumspatium
author_rank: Newbie
timestamp: July 15, 2018, 06:17:32 pm
content: Hi crews,I got a vintage 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 circuitry.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?Thank you in advance!

author: LateLesley
author_rank: Frequent Contributor
timestamp: July 15, 2018, 07:25:17 pm
content: Well I can't find the exact chip, but it seems to be some sort of "uP Supervisor" IC. They seem to be used to monitor the incoming power, and do controlled shutdowns or switchover to battery if the power is lost, and/or a controlled reset.something similar to this -https://datasheets.maximintegrated.com/en/ds/MAX801L-MAX808N.pdf

author: Maximumspatium
author_rank: Newbie
timestamp: July 15, 2018, 10:31:03 pm
content: QuoteThank you for your suggestions and the datasheets that look indeed very similar. Although it sounds logical now, I still doesn't fully get how that power switching works.It looks like there are at least three different power sources:+ 5 V (pin 8 ) ?+ 5V trickle power or standby power (pin 2) coming straight from the PSU+ 3.6 V (pin 7) from the backup batteryIf I'm reading the schematics correctly, the MCU (U17) is powered directly by U12 whose pin 1 must be therefore the output voltage connected to MCU's VDD(pin 13).I wonder what that strange S1 switch attached to pin 1 of U12 is supposed to do?

author: amyk
author_rank: Super Contributor
timestamp: July 16, 2018, 12:08:40 am
content: Which exact model is this? I know Apple published some (somewhat) detailed books called "Inside Macintosh" which might explain that circuit.According to the schematic, pin 7 receives a-3.6V supply from the battery.

author: oPossum
author_rank: Super Contributor
timestamp: July 16, 2018, 12:15:33 am
content: The battery is probably drawn backwards. The chip may be the PRAM and the switch would be for PRAM reset.

author: Maximumspatium
author_rank: Newbie
timestamp: July 16, 2018, 12:52:06 am
content: Quote from: amyk on July 16, 2018, 12:08:40 amThe schematics is for Quadra 840av but the picture was taken from PowerMacintosh 6100. Both machines use the same circuitry.Quote from: amyk on July 16, 2018, 12:08:40 amUnfortunately, Apple documentation on the logic boards back to 1990 doesn't give any details except some brief and general descriptions.Quote from: amyk on July 16, 2018, 12:08:40 amYeah, it looks like a mistake in the schematics.

author: Maximumspatium
author_rank: Newbie
timestamp: July 16, 2018, 01:04:23 am
content: Quote from: oPossum on July 16, 2018, 12:15:33 amYeah.Quote from: oPossum on July 16, 2018, 12:15:33 amBecause the PRAM is known to be implemented in the Cuda MCU (U17), I assume that the chip of interest is probably a power supervisor with battery backup switchover, smth similar to Max801/808 but an earlier version from around 1990, hence the marking "90". The pinout doesn't match anything I've seen so far...

author: oPossum
author_rank: Super Contributor
timestamp: July 16, 2018, 01:11:30 am
content: What is the voltage on PA5, PB0 and PC1 with power off?I think you will find they are all zero volts.

author: Maximumspatium
author_rank: Newbie
timestamp: July 16, 2018, 01:13:04 am
content: What bothers me is that small logo to the right. It looks like Apple logo but it's probably isn't. It could be a key in identifying the chip manufacturer.Any ideas on what this logo could stand for?

author: Maximumspatium
author_rank: Newbie
timestamp: July 16, 2018, 01:29:29 am
content: Quote from: oPossum on July 16, 2018, 01:11:30 amYes, that's true. Both pin 1 of U12 and pin 13 of U17 (Cuda VDD) reveal +3.64V. PA5, PB0 and PC1 are all 0V.

author: oPossum
author_rank: Super Contributor
timestamp: July 16, 2018, 02:31:19 am
content: Ahh, so the delta-in-triangle symbols are battery backed power. I saw the +5 by one and assumed is was the +5V rail from the power supply. That kills my theory of it being the PRAM.

author: lugaw
author_rank: Regular Contributor
timestamp: January 22, 2023, 05:38:47 pm
content: Hi,I need one of this IC since I got a Classic II with a corroded battery. Can someone post the voltages of the pins when the computer is on?Thank you.