Macintosh Quadra 700 Battery Leakage

[AlexTheCat123]

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) and it has some corrosion on the logic board from a leaky battery. When I was cleaning the corrosion off, several components fell off of the board. The parts that came off were R71, C61, R76, R77, Y6, and C65. D5, D6, and U91 are still on the board, but their pins don't look too great. U92 has nearly all of its pins broken off and it is hanging on by two or three pins. I tested the continuity of all of the traces that I could follow in the damaged area and everything seemed to be connected. When I try to turn the computer on, the power LED lights up and the speaker clicks once (but does not chime). Do you think that the symptoms are caused by the missing parts or are the power-on issues more likely the fault of bad traces that I didn't catch? If any of the missing parts are necessary for operation, please tell me the correct component value so that I can replace them. I hope that U92 is not needed for the machine to power on because it seems to be a custom chip that is probably impossible to find. Attached are some pictures of the damaged area so that you can see what I am referring to.

I hope I can save this one because I have always wanted a working Quadra 700!

 

[tattar8]

Speaker clicking but not chiming could be a ROM issue.  If the CPU can read the death chime from the ROM, it should play it.  I don't have a schematic for the Q700, but there's a good chance that chip is important (since most chips are).  At the very least, I'd start with replacing the components you can replace, along with repairing any broken traces, and see if you can get a death chime at least.

That chip is probably found on other Macs of the era as well, if you can get a parts board from one of them.

 

[AlexTheCat123]

Do you know the values of the components that I listed above? They disintegrated when I was cleaning the board so I don't know what to replace them with.

 

[tattar8]

There was a post here that had high resolution images of the entire board, but the embedded image links were all broken.  Here's a link to the actual images:

https://photobucket.com/gallery/user/bradwart/media/cGF0aDovMDMwNjQ5RDYtODFDNC00MTVELUI2M0ItQzZDMzREOEZCMUJCX3pwc3lxbzdkbWRpLmpwZw==/?ref=

You might be able to get an idea of what is missing from those.  Other than that, I don't have a Quadra 700 so I can't get any values for you; someone else on this forum would have to do that.

Also, if you're really determined, you might be able to scrape away at the edges of that chip to expose metal contacts for you to solder wires to.

 

[AlexTheCat123]

Thanks! I will look into that.

 

[AlpineRaven]

Ive got one as well - exact same problem as yours, re-soldered the resisters what fallen off.

Fired her up - I all I can is hear chime of death. I noticed 3x RAM chips isn't really soldered onto the board/corroded and one or two chips is dead/fried in my suspicion. At this stage I am saving up for heat gun so I can remove the RAM Chips and replace with new ones.
Cheers

AP

 

[AlexTheCat123]

Thank you for this advice. I will try to resolder the parts that fell off and I hope that my RAM chips aren't bad.

 

[AlexTheCat123]

Can someone upload some pictures of the area of the board near the reset and interrupt switches? I am trying to order replacement parts and I want to make sure that the component values are what I think they are. There don't seem to be any pictures of that area in the link that tattar8 provided above.

 

[Charadis]

Can someone upload some pictures of the area of the board near the reset and interrupt switches? I am trying to order replacement parts and I want to make sure that the component values are what I think they are. There don't seem to be any pictures of that area in the link that tattar8 provided above.

I’d be more than happy to when I get back later this evening, currently out of town for Easter Sunday. I’ll see if I can read the values of the components you listed. Unless someone beats me to it, of course. 

In the meantime, here is a pic I took yesterday, and I tried zooming at just the area you mentioned. Probably not much help, but it’s the best I have for now

 

[AlexTheCat123]

Thank you for the picture! Unfortunately, I can't make out the values of those parts, so those additional photos would be great!

 

[Charadis]

Thank you for the picture! Unfortunately, I can't make out the values of those parts, so those additional photos would be great!

Sorry this took a day! Hope this helps you out. 



Panned out over board



Tried to get as much of the SMDs on the left, just before being covered by the floppy/HDD assembly. If you'll need pics of the SMDs beneath the floppy, too, I'll be working on the system later this evening.

 

[AlexTheCat123]

Thank you! That is perfect!

 

[AlexTheCat123]

Can you tell me the code on capacitor C61? I can read all of the numbers on all of the components except for that one. 

 

[Charadis]

Can you tell me the code on capacitor C61? I can read all of the numbers on all of the components except for that one. 

I could be wrong, but it looks like IA5? I had another pic, but too much light glare, so I turned off the overhead light which darkened the setting for the pics above. 

I can can double check when I get back from work if the code is still not legible 

 

[AlexTheCat123]

Thank you for the pictures! I agree that it appears to say IA5. I believe this means that it is a 0.1uf capacitor.

 

[AlexTheCat123]

I have now replaced all of the parts that were missing, with the exception of C61, which I have not ordered yet, and U92, which is only hanging onto the board by only a few pins. I now get a startup chime when I turn the computer on and the reset and interrupt buttons seem to work fine. However, when I hooked the computer up to a monitor I saw that it had a sad mac error with the code 0000000F 00000001. Is this likely caused by the absence of U92 or is it something else?

 

[AlexTheCat123]

I tried desoldering and resoldering U92, even though it is missing some pins, and to my amazement this caused the computer to boot to the blinking floppy disk screen. It will boot just fine from floppy, but I now have two more problems.

1. The screen has a greenish tint to it. What is causing this? Is it my monitor or is it a problem with the computer?

2. The computer will not recognize or boot from a known good SCSI hard drive. At the blinking floppy disk screen, the drive's activity light flashes briefly every second or so, but the machine will not recognize the drive. What is wrong with the SCSI circuitry on the logic board? 

 

[olePigeon]

0000000F 00000001 looks to be a BUS error.  I've seen that error on my IIci when my SCSI drives aren't terminated correctly.  I wonder if U92 has something to do with the SCSI BUS.

1.  I think the green tint is because the monitor doesn't understand Sync on Green?  That'd be my guess.

2.  This could be related to the error you had already.  So maybe the SCSI BUS is still having issues and is preventing you from using a known good SCSI drive.  Also, are you certain the OS on it is compatible with your specific machine?

 

[AlexTheCat123]

I am certain that the SCSI drive has a compatible OS on it because it is running System 7.5. According to my research, U92 is the RTC and PRAM chip, so that shouldn't have anything to do with the SCSI bus, right? It is a relief that the green tint is probably not a problem with the computer itself. I was sort of nervous that I had yet another repair problem on my hands.