Macintosh Quadra 700 Battery Leakage

Bolle · Apr 25, 2019

U92 is the RTC/PRAM.

Without it you will get exactly what you are seeing now... booting from floppy works but SCSI doesn’t + periodic blinking on connected devices.

Had that before on a SE/30 with broken PRAM chip.

One of the VIAs is communicating with the PRAM on bootup. If that communication fails the machine won’t boot correctly.

olePigeon · Apr 25, 2019

Sweet, thanks Bolle. Looks like you have your answer.

AlexTheCat123 · Apr 25, 2019

Darn. I guess I won't be able to get the Quadra working after all because replacement RTC/PRAM chips seem to be pretty much impossible to find.. Thanks for all of the help!

Bolle · Apr 25, 2019

Someone really should look into how the communication between VIA and the PRAM part of the RTC/PRAM chip works.

It looks a lot like I2C or something similar...

Do we have the schematics for the Q700? You could wire in any RTC/PRAM from the SE through SE/30 and all other Mac II machines - they all work the same way.

You also need a crystal at Y6 or Y7 if you want the time to actually advance.

AlexTheCat123 · Apr 25, 2019

Really? If that is that case, then it would be really cool if someone could program a microcontroller to emulate the PRAM chip.

olePigeon · Apr 25, 2019

@AlexTheCat123 Is there enough metal left on the chip that you can solder wires and just run some jumpers?

AlexTheCat123 · Apr 25, 2019

Unfortunately, there is not. Five or six of the pins are broken off entirely and several of the pads on the motherboard have been completely eaten away by the corrosion.

Trash80toHP_Mini · Apr 25, 2019

Bolle said:
Someone really should look into how the communication between VIA and the PRAM part of the RTC/PRAM chip works.

It looks a lot like I2C or something similar..

From what I recall back in the day it is indeed I2C.

firebottle · May 13, 2019

AlexTheCat123 said:
I recently bought a Macintosh Quadra 700 off of eBay (https://www.ebay.com/itm/Vintage-Apple-Macintosh-Quadra-700-M5920-Desktop-Computer-w-Harddrive-Mac-iMac/273781054522?ssPageName=STRK%3AMEBIDX%3AIT&amp;_trksid=p2060353.m2749.l2649) ...

Strangely, this doesn't show up when you search for sold/completed auctions. Pretty sure eBay goes back at least 90 days... I searched for it today ...May 13, yours ended April 3. I've always wondered if eBay edits out auctions that don't go for big $$$ in sold/completed search results...

AlexTheCat123 · May 13, 2019

That is very strange. The link still works fine for me.

dramirez · Feb 22, 2024

Bolle said:
Someone really should look into how the communication between VIA and the PRAM part of the RTC/PRAM chip works.

It looks a lot like I2C or something similar...

Do we have the schematics for the Q700? You could wire in any RTC/PRAM from the SE through SE/30 and all other Mac II machines - they all work the same way.

You also need a crystal at Y6 or Y7 if you want the time to actually advance.

Hi @Bolle, by any chance do you have the Quadra 700 schematics?

Does a bad RTC will make the clock not to advance and MacTest to fail with: "One second Intrrupt Test failed"?

Thank you!

Macintosh Quadra 700 Battery Leakage

Bolle

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olePigeon

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AlexTheCat123

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Bolle

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olePigeon

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Trash80toHP_Mini

NIGHT STALKER

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