How to start a repair center

This page currently consists of tips from Nicholas Bodley's words of wisdom about electronics tech. We welcome expansions, revisions, and reorganizations of the material (in particular, advice on setting up the infrastructure of a repair center should be present here as well).

When I saw a collection of images of disassembling and reassembling an XO, my electronic tech. experience reminded me about a few matters that, imho, should be common knowledge for anyone doing such things:

Good things to know

Static-discharge damage

In industry, any even-moderately-competent assembly or service facility is almost religious about keeping people electrically grounded (I like the British usage, "earthed"). Especially in dry air, and especially with modern synthetic fabrics and other wearables, it's awfully easy to charge oneself up to several tens of kV. (That's kilovolts, 1,000s of volts, as you might well know.) If you're charged up to about 3 kV or less, you probably won't feel it when you discharge yourself suddenly to ground.

However, semiconductors can be destroyed (or, worse, degraded -- they work, but not as well/reliably) by roughly 100 volts. (Degraded parts can be nasty -- things seem to work, but not reliably.)

At least, low-cost wrist grounding straps (plastic conductive strips) should be considered; serious facilities would have real wrist grounding straps, which cost varying amounts from $few to $tens. Important is that people know how to make their own; a 1-megohm (value not critical; it could be half or two megs) resistor in series protects against accidental electric shock from the power lines ("mains"), and much of the world runs on 220 V or 240 V, significantly nastier than our domestic 120V.

The strap must connect ultimately to earth ground, of course.

Just how much need there is for wrist grounding straps is something a tech with experience in poorer countries could shed light on; as I see it, a motherboard unnecessarily zapped is very unfortunate.

In industry, there are conductive floors and "heel grounders" that go between your socks and the inside of the shoe, and extend around the outside to fit under the heel. There are also wrist strap and heel grounder testers (not cheap, btw!).

Screws

Another topic is screws. I don't know whether XO's have molded-in tapped (threaded) brass inserts for (machine [type]) screws to attach to (that's a very nice feature, but it adds cost).

If not, it's quite important that everybody who might take apart an XO should know that they must not simply reinsert the screws casually into plastic. About the third time somebody does that, the plastic is chewed up inside the hole, and the screw won't hold. Mechanical techs. call it "stripped threads".

It's good general practice, when reassembling threaded fasteners (including fire-hose couplings, where it's crucially important, and even a few food container covers) to put them into contact and turn the "wrong" way until you feel a click. Only then should you turn the correct way to engage the threads. With metal parts such as fire-hose couplings that have fine-pitch threads and relatively large diameters, it's quite easy to "cross-thread" and jam the threads.

However, where screws fit into plastic, it's different. The hole is molded in, and its size is "too small" for the screw, on purpose. When a screw is installed the first time, it forces the plastic aside to create mating threads.

When the screw is removed, of course the threads in the plastic remain essentially as they were when the screw was installed.

However, when the screw is reinstalled, it's really easy to misalign it (rotationally) so its tip starts to emboss new threads. If continued, that is quite likely to do serious damage to the existing threads. For that reason, the screw should be rotated backwards until you can feel a little "bump" as the threads align.

It might help to be aware that screws for plastic are something like wood screws -- they have widely-spaced threads. Machine screws (traditional term) have closely-spaced threads, and fit into metal, as you probably know.

Dealing with small parts

When disassembling, all small parts should be put into a small container (I can imagine a coconut shell!), and please, please watch for cats and waybe other pets that like to hit little things with their paws.

Once things work out, a shipment of XOs should include a kit of small parts to cover unwitting losses. (Might as well include a few low-cost wrist grounding straps with instructions (why, and how) in the local language, too.)