Tuesday, December 8, 2020

Recapping a Macintosh SE/30 and a IIsi logic boards and the IIsi power supply

Many vintage (15+ years) electronic boards (PCBs) are at a higher risk of having its non-solid electrolytic capacitors leaking by now. Such leaking occurs regardless of whether the component is actually being used/energized (although storage conditions may further contribute to the component degradation). The leakage happens due to natural aging of the component sealing and/or internal corrosion within the capacitor. The consequence of such leakages can be catastrophic not only for the capacitor itself, but for the electronic board as a whole. Here is why...

The most commonly used capacitor (aka caps) in computer logic boards and power supplies are the non-solid electrolytic capacitors, which use a liquid or gel as electrolyte. The problem is that the electrolyte liquid/gel used in these caps are conductive and corrosive and both these characteristics do not go well if spilled over your PCB. Therefore, when these capacitors leak, they can cause:

1) The PCB to malfunction by creating electric contact (short circuits) between components that were intended to be connected. Depending on the short circuits created by the conductive liquid, it could completely burn components and even create holes in the PCB, potentially damaging the board beyond repair. 

2) In addition to shortening components, the corrosive nature of the electrolyte will (with time) corrode the copper traces on the PCB as well as the components terminals to a certain extent. The electrolyte will also cover the solder joints creating a crusty layer that shields the solder joint from heat, requiring you to add more heat to be able to remove components (by desoldering).

Macintosh IIsi Power Supply with leaky capacitors

To demonstrate the technique used to replace leaky capacitors, I am going to use 2 logic boards from vintage Macintosh computers: a Macintosh SE/30 and a Macintosh IIsi.

In order to repair PCB boards with leaky capacitors, you will need to:

1) Identify and order new capacitors (I recommend using mouser.com);
2) Take several high-resolution photos of the board with the old caps;
3) Remove the old capacitors;
4) Throughly clean the board(*);
5) Prepare the solder pads for the new capacitors;
6) Install the new replacement capacitors.

IMPORTANT: It is highly recommended that if you dont have much soldering experience that you gain some practice with some scrap/trial boards to avoid damaging your precious/rare boards. Also, watch some videos on YouTube from a recap professional known as Bruce form Branchus Creations (I learned A LOT from his videos and live streams).

(*) to clean the board you can use a toothbrush and scrub it with distilled water with a bit of soap, rising with isopropyl alcohol and let it dry for at least 24 hours. Alternatively, you can use a large ultrasonic cleaner for a deeper and hands-free cleaning. 

It seems even silly to mention, but do not start until you complete the first and second steps. Take several high resolution photos of your logic board to identify each capacitors location and polarity. Or alternatively, you can download very good Mac capacitor guides again from Bruce's website at http://recapamac.com.au.

There are basically 2 techniques to remove the old surface mount (SMD) capacitors present in these 2 logic boards: by desoldering them OR by breaking their terminals with mechanical fatigue (twisting it with pliers/tweezers). When dealing with such rare vintage/unique computer boards such as these, I usually opt for the desoldering method which offers less risk of damaging and lifting the fragile soldering pads out of the motherboard. 

To desolder them, I used a relatively cheap but good hot air station from Baku model 858A. There are several clones that go by the same model number.

Macintosh IIsi Logic Board with the caps removed

Following a precious advice I again learned from Bruce, note on the photo above that I have some exacto knives blades and springs near the board. I used these blades (springs to hold them in place) to shield the heat from the desoldering station from  hiting other components nearby, especially plastic connectors that could permanently be deformed due to hot air.

Close-up look of the IIsi board without the caps

Macintosh SE/30 Logic Board with the original caps

Check this video I made with a digital microscope showing the removal of the old caps, cleaning of the pads and installation of the new capacitors:

For the new capacitors, I decided to use the leaky proof option of tantalum caps. Unlike the common electrolytic, tantalum caps use a solid electrolyte as opposed to liquid or gel that as we've seen, can eventually leak.

To solder the new tantalum capacitors, I used this budget model FX-600 soldering iron from Hakko (a recommended high-quality Japanese brand) with temperature control. 

The Macintosh IIsi logic board with new tantalum caps

The Macintosh SE/30 Logic Board with the new tantalum caps

Now, moving on to the power supply:

Macintosh IIsi Power Supply opened

Power Supply board removed from the case

Capacitor juice marks everywhere on the board and corrosion present

After cleaning the board with distilled water+soap and rinsing with alcohol

Installing the new capacitors in the power supply

Note the corrosion on the copper near the old caps, you can scrap this off for a better look and apply new solder mask

New capacitors installed

Power supply assembled

Fixing the new caps with hot glue to replicate the original fixture

I left a note inside to show to the next technician when it was last recapped :)

These vintage boards and power supply are now ready for the next 30 years!


  1. Thank you for the feedback and words of encouragement! It's much appreciated :)

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