68kMLA Classic Interface

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Classic II Recap Project
Posted by: IIfx on 2017-10-19 13:45:21
After many years of procrastination, I decided to tackle my first 68k recap. I relearned soldering when I recapped a chinese OTA DVR, so the Classic II should be doable.

My Classic II became unusable in 2011. The repair work is well overdue.

I used the wire cutter/sharp pliers method to remove the caps and only lifted 1 pad. I guess I am lucky?

The situation looked bleak prior to the 90% proof alcohol bath:



After the bath with toothbrush scrubbing of the board:



90% IPA will neutralize the acidic electrolyte remaining on the board, correct? Hopefully this board is salvageable. I have 1 spare, also with leaky caps.

Tantalum or Aluminum Poly? I can't decide.
Posted by: 68krazy on 2017-10-19 14:48:42
If you go with aluminum polymer, there is no risk of putting one in backwards and having it burn up like there is with tantalum. When they fail, they fail open.

I’ve done two tantalum recaps myself, thinking about going poly for the next vintage mac I have queued up (which is, coincidentially, also a Classic II).
Posted by: PB145B on 2017-10-19 17:28:33
I can’t help but notice that you have two bent pins on your CPU that appear to be touching! What I do to fix these is take a sewing needle and very gently straighten them.
Posted by: IIfx on 2017-10-19 20:22:19
I can’t help but notice that you have two bent pins on your CPU that appear to be touching! What I do to fix these is take a sewing needle and very gently straighten them.
:O Thank you for pointing that out! The pliers must have hit those pins. 
Posted by: PB145B on 2017-10-20 02:50:20
You’re welcome! Yeah those pins are very easy to bend.
Posted by: aplmak on 2017-10-20 07:14:10
Excellent catch on those pins!!! Yeah the Classic and the II are a pain in the #$%()#... I've been using tants for years.. maybe had one or two burn up.. no big woop.. I just desolder and put on new ones.. The X2 safety caps on the old power supplies really burn and pop and smell....
Posted by: IIfx on 2017-10-23 14:39:28
I ordered the caps from DigiKey. Mostly aluminum polymers with a few tantalum where I could not find matching AlPoly caps. Both my main Classic II and my Color Classic will be getting logic board re-caps done this time around. Total component cost was $22.

The SMD soldering technique documented at http://www.co-bw.com/DIY_Replacing_SMD_capacitor.htmlooks promising. I ordered a tube of low-temp solder paste. Supposedly the paste should help secure the cap while you apply heat to it with a soldering iron.

Finally my nice Hakko soldering iron will get some good use!

It seems AlPoly caps hold up well. My old AMD Phenom II desktop with an Asus board has AlPoly caps. They survived the heat and abuse of an extreme overclock for many years.

Edit:

Perhaps I will film the process of recapping so everyone can mock my poor soldering skills/twitchy hands. Someone may find it interesting or practical.
Posted by: IIfx on 2017-10-26 16:16:42
I didn't bother documenting my repair on film. Unfortunately something is still wrong as the system does not boot. I could not replace one of the capacitors at the back right corner of the board, it is just too tight of a fit and I am missing a pad. It looks related to sound.

The Mac will power on, but will display a grey screen with 2 large vertical black bars. Any ideas?
Posted by: beachycove on 2017-10-26 17:59:35
The SMD soldering technique documented at http://www.co-bw.com/DIY_Replacing_SMD_capacitor.htmlooks promising.
Thanks for that link. It explains much that I have wondered about.
Posted by: jack on 2017-10-28 18:30:38
I used the wire cutter/sharp pliers method to remove the caps and only lifted 1 pad. I guess I am lucky?
Used a hot air rework station to recap a Classic II this morning... highly recommend for future recaps! I had all the caps off in less than a couple of minutes, no need to worry about lifting pads. They came off like butter.
Posted by: Bolle on 2017-10-28 23:56:50
Problem for me with hot air is that caps sometimes start to cook up their remaining innards faster than the solder underneath can melt and end up releasing a toxic stream of smelly fumes 😎

Caps are weak anyways otherwise they would not have leaked in the first place, so they tend to vent even faster when heated up.

Take caution with hot air and better do it outside if possible.
Posted by: jack on 2017-10-29 07:25:28
Yeah... I was lucky to only have one release fumes. I was in a well-ventilated area, so was not a big issue.
Posted by: IIfx on 2017-11-01 14:56:09
Anyone have any ideas as to why the Classic II isn't booting still with new caps? I washed the board well. The bootup process reveals a grey screen with two large vertical black bars. Could it be the missing cap at the back right corner of the board? The pad lifted so I have no easy way of fixing that.

I might send the 2 Classic II boards off to a proper expert as they are too far gone for my own diagnosis. Anyone willing to make a deal?
Posted by: chu-oh on 2017-11-01 20:40:02
Just on the subject on de/recapping - I got one of these suckers when I did my Plus analog board: https://www.ebay.com.au/itm/Pro-Dual-LCD-Digital-Soldering-Desoldering-Station-Iron-Gun-2-in1-ZD-917-Rework/272856139965?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The quality build isn't amazing but takes off caps quickly and cleanly, would highly recommend.  
Posted by: bibilit on 2017-11-02 00:20:23
Anyone have any ideas as to why the Classic II isn't booting still with new caps? I washed the board well. The bootup process reveals a grey screen with two large vertical black bars. Could it be the missing cap at the back right corner of the board? The pad lifted so I have no easy way of fixing that.
Maybe a problem on the Analog Board, if the 5 volt is low, you can have this kind of behaviour.

Analog boards should also have new capacitors (at least) on the secondary side.
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