Macintosh Quadra 700 Battery Leakage

[Bolle]

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]

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

 

[AlexTheCat123]

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]

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]

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

 

[olePigeon]

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

 

[AlexTheCat123]

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]

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]

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&_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]

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

 

[dramirez]

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!

 

[theletter0xff]

oh a second resurrection ..
I also have a battery bombed Q700, the crystal oscillator at Y6 lost a leg to rust; I do not know if I will be successful grinding away the housing to solder on a jumper. It took a while to find its specs so:

Y6 & Y5 Crystal Oscillator, clock xtal, 32.768Khz, smd part labeled 197S0001, 4x10x3.2 mm. I cant identify the manufacturer from the logo, but it's a similar package to the Meritek MXT7.

Apple Quadra 700 Schematic; page 26, "Sound Input Circuitry & Real Time Clock";

Macintosh Quadra 700 & 660AV Schematics : Apple Computer Inc. : Free Download, Borrow, and Streaming : Internet Archive

OEM Schematics for the Apple Macintosh Quadra 700 and 660AV Computers.

archive.org

and https://www.macdat.net/repair/apple_schematics.html

@AlexTheCat123 did you get your Quadra 700 working again?