Guide to cleaning a PCB: How Coke nearly killed a Mac Mini

During Dan’s second week his Mac Mini died. He was certain that if I didn’t have reason to fire him before, that I did now. Lucky for him I was on vacation and knew nothing about what happened or even cared. When I got back we spent some time trying to figure out how, what seemed to be a normally working machine, suddenly stopped working.

Upon taking it apart (I really wish I had taken pictures) I noticed there was some familiar looking dark residue on the bottom of the case and on the board as well. Having drank tankers worth of the stuff I quickly identified what appeared to be Coke syrup. Had my favorite beverage killed this Mac Mini, or was it just a coincidence? I didn’t remember spilling anything, at least not recently. Jon had spilled some almost a year ago, but that seemed too long ago to make a difference.

I dabbed up what I could with a paper towel re-seated everything and slapped it back together. Hoping the hard drive was at fault, even though it refused to turn on at times, I was able to get it going long enough to reformat it, and bring everything up-to-date.

No more then an hour in to Dan using it, the machine shuts off again and refuses to turn on. So much for it being the hard drive. It seems like the Coke was heating up and actually bridging some of the points on the board. Assuming it probably shorted out I pronounced it dead and stuck it in a drawer.

There the Mac Mini sat for months all but forgotten until it’s hard drive was scavenged. I decided it was time to pitch the thing unless there was some way to fix it. I consulted Google, Mr. O, and Steve Marchesani. It seemed like I might be able to wash it and remove the residue which may be causing all of these problems. I still risked doing all of this to find permanent damage, but it seemed like a good idea at the time.

The Guide

Tools & Materials
– Mac Mini take-apart tools (2 thin putty knives)
– PCB cleaner spray from Radio Shack
– Distilled water from the pharmacy
– 2 cans of compressed air
– Liquid damaged circuit board (Mac Mini logic board in this case)

Step 1
Take the device completely apart. After getting the case open the Mac Mini doesn’t have too many internal components, and the only one that appeared to be affected was the logic board itself. It is important to remove anything that will come off, there is no need unnecessarily subject other things to this process. The heat sink, though technically removable didn’t seem to be worth the time, and getting it back on would have most likely ended in disaster.

Step 2
Go at the board with the PCB cleaner and complimentary brush attached to the nozzle. Over the sink seems like a good place. The cleaner appears to be something like WD40, which people said they have used to clean printed circuit boards (PCBs). I wasn’t sure how conductive WD40 is and wasn’t going to find out given the availability of a substance that clearly states that it is safe for use on a PCB. The stiff brush seems like it would break the bonds on the board, but nothing seemed harmed as I sprayed and moved the brush across the surface of the board. Not clear on where the Coke went, I drenched the board in the cleaner and scrubbed everywhere I could get at.

Step 3
Warm some distilled water in the microwave. Next do the unthinkable, drop the whole board in a shallow pool of the warm distilled water. People fill their entire computer cases with mineral oil in the name of cooling. Any other liquid doesn’t seem that harmful considering that. Distilled water, in theory, is free from any of the junk that may be found in normal drinking water. Depending on where you live or your pipes it could be anything. I did read about people putting the board under the shower, which doesn’t seem to provide any obvious benefits. Others suggested the cold cycle on the dishwasher (without any detergent), some said use the warm cycle, some even said use detergent. Though drastic, I don’t see how its much more effective, and you are likely leave deposits behind that will corrode the board over time or just make things worse. While the board is taking a bath it couldn’t hurt to use the brush from the PCB cleaner to give the board some additional surface cleaning.

Step 4
After soaking for a little rinse the board with any remaining distilled water. The bath which managed to dissolve any remaining Coke syrup is now filled with impurities, none of which you want hanging around after spending all this time.

Step 5
Proceed to use the compressed air to blow the water away. This works far better then you might suspect and gets water out of those hard to reach places like inside the DVI connector. If trapped in a small space, water may take quite a while to evaporate on it’s own. The high pressure, especially when using one of those little red straws that come with the can, forces most of the water out. If you don’t use an entire can of air then you’re probably not trying hard enough.

Step 6
Wait. Even though the board may appear dry, and it might even be, there is still the chance that water may be lurking somewhere. The Mac Mini has a little piece of foam that’s affixed to the board, which was still damp. Place the washed unit somewhere safe and with adequate ventilation, preferably where you will forget about it for a few days. I left it alone for a week which was probably more then enough.

Step 7
Check for signs of damage. Physical damage that may have occurred during the cleaning process can only lead to even more destructive things when you put it all back together and plug it in. Also check for corrosion / oxidation, if the water was clean none should be present. There also shouldn’t be signs that any liquid was present at all. If any area appears blackened its already dead and you now have a rather clean but useless board.

Step 8
Put it all back together, but only enough to make it work and not get shocked. There is no reason to go though all the trouble if it’s not going to work when fully assembled. In the case of the Mac Mini that required just about everything except for the top case. I plugged it in fully expecting the circuit breaker to pop soon after, or something to smoke. Making it that far I proceeded to push the power button. Still no smoke, and a comforting, but loud Mac Startup tone (I guess the case muffles that).

Much to my surprise and a few hours of testing the Mac Mini lived again. It needed a hard drive, and didn’t like a ViewSonic display unless it was using the VGA adapter, but other then that it worked normally. I even ran the graphing application with the 3D examples to sap up as much of the CPU as possible and left it on over night to simmer. It survived the night without any noted problems.

Currently the resurrected Mac Mini is spending it’s time connected to my TV serving as a pseudo Apple TV. I still don’t fully trust it. Each time I go to wake it from sleep I expect nothing to happen, but so far things have been fine.

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