Retrobyte

I recently acquired an Apple Macintosh Classic II, the last of the iconic black & white compact macs. Sadly, it was suffering from an issue common to a lot of these old macs, in that when switched on you are presented with the following screen,

The root of the problem is that the capacitors on the motherboard have started to leak and unfortunately the fluid is conductive and plays havoc with the surrounding ICs.

In theory, it’s fairly easy to open the Mac up, however note the two torx screws at the top of the case require an especially long screwdriver to reach them.

Once open, the power, floppy and hard disk cables can be unplugged and the motherboard removed. Close inspection of this machine showed that capacitor fluid had clearly got onto sensitive parts of the pcb.

Fortunately, if this residue can be removed then it’s likely the Mac will once again be able to boot. The question is how to go about that. Ideally you would painstakingly work on the areas with a soft toothbrush and isopropyl alcohol, however this can very time consuming and the clear fluid makes it very difficult to know if you have got everything.

There is an alternative that seems more foolhardy than brave, but anecdotally across the web seems to yield good, long lasting results. Which is to simply put the motherboard in the dishwasher.

To ensure the best outcome, the following approach is recommended.

• Remove the main IC ROMS
• Use your dishwashers cool/delicates wash programme
• Put in only a small amount of dishwasher detergent

Once the board has been through the wash cycle, it’s imperative to ensure that is completely dry before reassembling. Forty-eight hours in a warm place, such as an airing cupboard is advised, plus the use of a compressed air cannister to remove water from under sockets.

Also, this is only ever a temporary fix. Over time the capacitors will leak more causing the problem to return. The only permanent solution is to have them replaced. As it it will be a while before I get a chance to do this, I used some conformal coating to protect the surrounding ICs.

Reassembled and time for the moment of truth!

In general, this macintosh is once again full operational, but sadly the startup bong is missing. The loss of fluid from these capacitors has been enough to lose all audio. Hopefully a full recap will restore it.

I recently acquired an IBM PS/2 Model 35SX (8535). It was overall in very good condition, however it quickly became obvious that the floppy drive had suffered the fate that seems to await all PS/2 floppy drives, a complete inability to read or write disks.

PS/2 floppies are notorious for the failure of the SMT capacitors on the logic board, resulting in the drive still functioning in terms of head movement and LED activity, but any attempt to access a disk results in,

On opening the drive, close inspection showed that some of the capacitors had clearly leaked and I had little confidence the remaining ones were going to be of much use. In situations like this when recapping old electronics, it really makes sense to replace as many as you can in one go. If some have failed it’s likely others will fail in the near future.

The capacitors are very small and removing them, whilst not damaging the pads is difficult. There are a number of suggested approaches, I ended up cutting most of the capacitor away with some small sharp wire cutters. I could then gently heat the pad and the last bits of the legs came away cleanly.

Once the original capacitors were removed and the leakage cleaned up, the next problem was sourcing and fitting replacements. Given the poor state of the pads and the difficulty in soldering surface mount parts, it was easier to use leaded replacements.

As you can see they are substantially larger and are obviously designed for through-hole mounting. The trick was to take advantage of the excess length of the legs to bend them into a shape, so that when the capacitor was laid horizontally, a portion of each bent leg ended up making reasonably firm contact with the pad (taking care with polarisation where necessary).

With a little bit of masking tape to secure the position, solder could then be applied to the bent leg and pad and once each leg was secure, the excess lead could then be snipped off.

With capacitors replaced, the drive heads were given a quick clean and the unit reassembled for testing.

Success!!