Damaged Mac motherboard

[Echoes]

Hello everyone, I bought my first 68k Mac (a Classic) last week and now... I'm here

The problem is, while the case was in perfect condition, once opened it revealed an horrible mess: the battery leaked its acid on the mainboard, and now I'm trying to save (should I say resurrect?) this poor little computer.

Here's the flickr set of its condition before treatment. Viewer Discretion Is Advised (and I'm not posting any rusted metal frame pictures because those are really scary, sigh).

It now looks better as 99% of the acid is done and I'm going to de-oxidize it in the next days, but after all the cleaning a few components are missing:

• The battery holder
  
• The D2 transistor
  
• Y1, which I don't know what it is.

So, do any of you know anything more about those components? I know there are Larry Pina's books that are very useful for repairs but I don't know if they contain the schematics too. Do you have them?

 

[Theretrogamingroom]

I don't think you could "Fix" that. You will probably need a new motherboard.

xx(

 

[LCGuy]

Even if you did replace the damaged components, I'm going to take a stab that the acid has likely corroded some of the circuit traces...I'm sorry to have to say it, but I'm going to agree with Theretrogamingroom - that board looks to be a total loss.

 

[Solvalou]

Mate, that board is a write-off. I thought my IIfx had bad battery damage and that had 2 of them! I'm sorry to say but yours takes the biscuit. 8-o

There was no way in hell mine was repairable and this certainly isn't.

P.s. If your curious heres a reference: viewtopic.php?f=4&t=15612&p=148671#p148671

 

[Echoes]

Sigh. It took so long to find a Compact Mac... In Italy, Apple never sold much, until the advent of OSX and iPod and all that stuff.

Well, I'll post the result of the acid cleaning tomorrow, and try to check the traces with a multimeter anyway. Except for the hours spent working on, it it's not gonna cost much money on components, so I think I won't drop by the wayside in just a week even if i know it's gonna be useless. xx(

Update: those are three pictures of what the board looks like after the acid removal.

 

[Unknown_K]

It looks like quite a few traces have gone bad, and some chips need replaced (not worth the effort). Find a new motherboard.

 

[Mk.558]

A Classic motherboard shouldn't be that uncommon. Someone here or on LEM swaplist might ship one over th're.

 

[Theretrogamingroom]

You *may* get it to work for a while, but you would need to replace all of the bad capacitors (I would suggest all of them), any chips that have been corroded, anything that is missing and you would really need to get the rest of the rust off (I would suggest doing that with an eraser). And even then it would probably be on its last legs.

But if you want to give it a jab and you get it to work (And have it work for a while) it would make one heck of a success story. But again, I wouldn't get my hopes up. Your best bet is getting a new motherboard.

 

[Echoes]

Thank everyone for the advices. I'm looking forward to buy a new motherboard, but meanwhile as I said I'm going to try to work a bit on this one too.

Does anyone know how what that Y1 component is/was? Or at least if there's something writteng on it to help its identification.

Also, do anyone know if D1 is PNP or NPN?

 

[phreakout]

Y1 is a crystal. I think (Someone re-check me on this value, please!) the value is rated at about 31.768 Khz. It may be similar to ones used on Mac SE, SE/30, IIx and other model Macs from that era. I'm not sure what value D1 is, since I don't have any Classic I logic boards for reference. It could be a 2N3904 or something different. Can you check the ID number on the flat side of that transistor, please?

73s de Phreakout. :rambo:

 

[Echoes]

Y1 it's probably 32.768khz then, it's a fairly common value

 

[SEthirty]

My SE/30 had also a exploded battery.

Believe me, I'm a technician, and it is practically impossible to fix te board.

Luckily I found a new SE/30 for €20,-, so that problem is already solved :beige:

EDIT : I forgot to say that it is practically impossible to remove all of the battery-acid.

I tried 5 different sorts of cleaning methods (no, I didn't do anything with a gas-burner :lol: ) and the acid is still there, although a lot less.

 

[trag]

I suspect that the other posters may be correct, but if you're going to try to fix it...

Rinse the board with a weak vinegar (use white vinegar) solution or similar. The battery leakage, in this case, is a base, not an acid, IIRC. Ah, just did a search, and it is indeed a base. This link may have useful PCB repair information: http://forums.arcade-museum.com/forumdisplay.php?f=14

This is the one confirming alkali/base batteries: http://forums.arcade-museum.com/showthread.php?t=117707

Fortunately, the region of the board which was exposed seems to have a lot of blank or filled areas and not too many vias (holes connecting one layer of the board to another layer of the board). Also, it looks like the solder mask (green stuff) protected the board for the most part. The only areas likely to be damaged are exposed copper and solder at the pins of chips and in vias.

Unfortunately, there may be some of these under the chips as well as the ones that are visible.

While the chips look bad, the damage should be only on the package/pins, and not the internal silicon. So as long as you can clean up the pins and don't break any off, the chips may be recoverable.

That sound chip looks like it needs to have all of its pins cleaned and resoldered. There's at least one other in those pictures that also needs that. You probably need to remove the chips and check the pads underneath to see if there's anything left of them. Also to check for any vias which may be under the chip.

Use a heat gun or hot air gun to remove the chip and be really really gentle with it. Use plenty of flux on the solder joints before desoldering. Also, you may wish to cover any surrounding small components (SM resistors or caps) with modeling clay so that you do not accidentally desolder them.

When you desolder those components, don't apply any force lifting the chip. Make sure all the solder is fully melted first. You must be extremely gentle in this case to avoid tearing or lifting pads (or what's left of them).

Check the continuity of all of the traces connected by vias. The vias which connect to capacitors probably go to the ground or power planes, so you can check their continuity to any 5V or GND connection.

The battery holders are still available. I know DigiKey sells them. There is probably a European supplier.