68kMLA Classic Interface

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Macintosh Classic II capacitor blues
Posted by: ThomRMkIV on 2016-06-05 15:53:10
Newbie here!

I picked up my second compact Mac the other day, a Classic II. My first was a Classic that had a very bad PRAM battery mishap... It is beyond repairable and wouldn't even power on.

This Mac Classic II works wonderfully and is in pristine condition (zero yellowing, see image comparing to a yellowed classic) but as per usual, the capacitors are leaking which causes video corruption. I took the board and quickly washed it in warm water and that fixed the issue for about 24hrs until last night when the problem came back. I cleaned it again but this time I used rubbing alcohol on a q tip and I think I got rid of some more leakage because it works again. 

Right now I'm on a tight budget so I can't afford to send my Mac out to someone to be recapped. I was thinking of doing it myself as a fun experiment as I do know how to solder but I have no idea what exact type of capacitors I need to buy. I know I need 10uf 16V, 47uf 16V and 1uf 50V but there are so many types of capacitors (solid, tantalum, ceramic) I don't know what works and what doesn't. 

In the meantime I'm also curious as to how I can prolong the temporary solution of washing the board. Not only do I want to enjoy my newly acquired Mac, but I want to make sure the caps don't leak so much that the board becomes damaged. 

Thanks for checking out the post!

Regards,

Tom
Posted by: naryasece on 2016-06-05 21:23:01
Oh neat, I just recapped my Classic II last week (it was my first attempt to recap a motherboard).

I bought enough capacitors to recap either type of Classic II boards from www.mouser.com (as I didn't have the computer open at the time of buying the capacitors). It was $11.25 including shipping. I opted for Panasonic Aluminum SMD passive capacitors (similar to ones I thought were already on the board) that would last at least 5000 hours

http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-SMD/_/N-75hqx/. Their search form looks complex at first, but was able to find the components I needed by entering the capacitance and voltage rating.

Sorry I don't have any tips on prolonging the temporary fix!
Posted by: Paralel on 2016-06-05 22:09:01
It general, its not a good idea to use a board, even after it has been washed to get rid of the crap, and it appears to be working. The caps are important, you risk permanent damage running the machine with busted caps. Something happening is rare, but it does happen every so often. Using a machine without working caps puts alot of stress on it.

As far as caps, go tantalum. You don't want to have to go through this again with electrolytics again in the future. Just remember to respect polarity with regard to tantalum, otherwise, POOF. They never take kindly to polarity reversal. I don't think the Classic II has any issues with the silkscreen being wrong with regard to polarity, might want to check with one of the pros just to make sure.
Posted by: bibilit on 2016-06-05 22:39:33
Just remember to respect polarity with regard to tantalum, otherwise, POOF. They never take kindly to polarity reversal. I don't think the Classic II has any issues with the silkscreen being wrong with regard to polarity
Keep in mind also that with tantalums, the line is for the plus side, when with SMD the black line is indicating negative.

The Classic II is a bit tricky, a lot of tiny caps, the Classic is far easier.
Posted by: ThomRMkIV on 2016-06-06 18:04:04
Thanks for all your input guys! I talked to a fellow enthusiast and he pointed me to some nice ceramic caps that didn't have polarity either, so soldering them would be easier and less of a hassle. I will have to purchase them and purchase a new soldering iron as my fathers is way too old and large for this job.
Posted by: Elfen on 2016-06-06 18:33:59
Which Classic II is it? There is one with 4 ROM Chips and another with 2 ROM Chips. See Uniserver's Caps lists on his site:

http://maccaps.com/MacCaps/Capacitor_Reference/Entries/1991/10/21_Macintosh_Classic_II.html

http://maccaps.com/MacCaps/Capacitor_Reference/Entries/1991/10/21_Macintosh_Classic_II_Revision_2.html

The recap is fairly easy. The Tantalum Caps are reversed Polarity to the Electrolytics, so the band on the old electrolytics are negative, the band on the Tantalums are positive.  But Tantalums are expensive. You can use non-polarized ceramic SMD/SMT caps, they will work great and costs a lot less.

I did the recap on my Classic II in less than a 1/2 hour's time. When you remove the old cap, scrub down the area under where the cap was with alcohol and a q-tip. There will be a lot of cap goo there to remove. When I did my recap, I used both Tantalum and Ceramic Caps and she fired right up!

To remove the caps, use the wiggle technique Ferrix97 uses on his video here (and a couple more he did): https://68kmla.org/forums/index.php?/topic/23893-powerbook-145b-also-for-140-160-145-display-capacitor-replacement-video-tutorial/

Then check the pad connection from the cap to where ever it is going too with a meter, and solder in the replacement cap.

Have fun and good luck!

EDIT: Also ask around. There are a couple of members with spare Classic boards which you can buy cheaply from them to restore your Classic with.
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