Disasters

Q: What should go into an emergency toolkit?

A: Partially flooded photography equipment can often be recovered for immediate re-use, provided that: (a) Someone knows how to strip-down and reassemble the equipment, and (b), action is taken before corrosion begins - ie., immediately. If you don't know how to reassemble the equipment, you can still stop the corrosion by taking appropriate action; but you will need to understand how to work with high voltages when dismantling any piece of equipment which contains a flash tube (and that includes compact cameras).
A suitable tool kit is as follows:
A set of good quality watchmaker's screwdrivers; and various small tools, eg., pliers, wire-cutters, adjustable spanner, Swiss army knife.
Tweezers, preferably fine pointed with curved tips. It is doubtful that anyone has ever successfully repaired a small-format camera without using tweezers.
A 1 litre bottle containing distilled water. Water is the best solvent for removing salt deposits, and it does not dissolve lubricants and adhesives. Distilled water leaves no residues after evaporation. De-ionised water can still contain dissolved organic material and should be regarded as second best. Drinking water is better than nothing, but in hard-water areas may contain as much as 0.5g/litre of dissolved solids.
Never wash out a camera mechanism with alcohol.
Cotton buds and paper towels.
Small self-sealing plastic bags for cataloguing the parts.
A pencil and writing pad for making notes.
A small soldering iron and some flux-cored solder. Soldering irons are available for field use, powered by a gas cartridge, or from a 12v battery*.
A 56W 10W ceramic bodied resistor, with insulation sleeving on the leads: for discharging flash capacitors.
A tube of Molykote 111 O-ring lubricant (or Molycote FS1272 for silicone O-rings).
A Pocket Multimeter (A,V,W); for testing cables and batteries, and for checking that flash capacitors have been properly discharged. There is really no excuse for not owning a multimeter - a cheap one can be bought at the local market for about £10.

* Soldering: Nowadays this issue is complicated by the increasing use of lead-free solder. After July 2006, it is intended that all new commercial electrical and electronic equipment available from within the EC will be lead-free once existing stocks have been sold (RoHS legislation). SnPb solder will remain available for repair and reworking. Leaded and lead-free solders should not be mixed (use different bits for the different solders) and the lead-free solders have a higher melting point than the traditional 60:40 SnPb alloy.

Q: What should I do if I flood a cable or connector.

A: If you flood a cable with sea-water, there is very little which can be done to save it other than to cut it back to a point where the water is thought not to have penetrated. The problem is that capillarity will cause the water to penetrate between the strands of the conductors at an enormous rate, and after a few weeks the conductors will turn into a green amorphous mass of copper chloride, and will go open-circuit. The only thing to do therefore is to salvage the connectors (if you can) and wash them, and throw the cable away. It follows, that if you don't carry spare cables, and you don't discard cables which have become wet on the inside, you can expect your photography expeditions to be terminated unexpectedly from time to time.

If you take spare cables, the problem remains of how to save the equipment into which the failed cable was plugged. The point to watch here is that the back-up seals between connectors and electronic modules (flash units, housings, cameras, battery packs, switch units, light heads, etc.) are often either non-existent or don't work, and you must establish the extent of water penetration or risk writing the equipment off. First-aid involves washing the connector several times from the outside with distilled water and gently blowing it clear with compressed air. The next step is to dismantle the equipment and see how much water is on the other side, but you cannot do this if you are not competent to deal with any hazards which may exist, i.e., high-voltages or fire-hazard due to high energy-density batteries. If the show must go on, you are faced with the risk that something may short-out at any time due to water droplets moving around. The best course of action therefore is to take the items which have been connected to the failed cable out of service (remove all batteries, unplug all cables, etc.) and do not use them again until they have been stripped-down, checked, and cleaned.

Q: What should I do if I flood a flash unit?

A: Some strobes have a battery compartment which is isolated from the main electronics section. If you flood only the battery compartment, you should wash it out thoroughly with distilled water and allow it to dry. If the contacts later begin to corrode, get them replaced. If you scrape the contacts to clean them, you will remove the plating and make them unreliable. After a battery compartment flood, look through the flash window for signs of water in the electronics section - the inter-compartment seals don't always work.

If you flood the electronics compartment, the best way to minimise the cost of repair is to open the unit, remove any salt contamination, and dry everything. The problem however, is that there may still be dangerous high voltages present, even with the batteries removed. A portable flash unit uses a low voltage battery to charge a high voltage capacitor by means of a device called an inverter (the thing that makes the whining noise). One charged, the capacitor can remain dangerous for months, it contains enough energy to kill frail individuals, and it will spray you with moulten metal if you accidentally short it out. If you don't know what you're doing, its best to leave the electronics well alone. If you go so far as to open the case and pour out the water, you must ensure that no-one can unwittingly come into contact with the exposed circuitry (or risk a conviction for criminal negligence! - don't forget that cleaners will come into your hotel room while you're out diving). Bear in mind that salt water is a good conductor of electricity, and may form an unexpected circuit path to your body as you handle the equipment. Do not try to wash the electronics unless you are sure that all of the high voltage capacitors (there may be more than one) are discharged, do not wash areas which are not already wet, and do not try to discharge capacitors by shorting them. Household rubber gloves are not sufficient to protect you from electric shock.

If you have some electronic knowledge, you may be able to recover a flooded strobe, provided that water-induced shorts have not destroyed any of the components. Some strobes have a dump resistor which is connected across the main capacitor when the power switch is set into the off position. Consequently, if you discover a flood, you should switch the strobe off in addition to removing the batteries. Once the housing is open, identify all of the high voltage flash capacitors, and the commutation capacitor, and discharge them individually by applying a resistor directly across the capacitor terminals. A 56 Ohm 10W resistor (ceramic bodied, not bare wirewound) with insulating sleeving on the leads, is suitable for strobes up to about 200J (it will get hot). The main capacitor may consist of several large electrolytics, either in parallel, or switched to provide selectable output power (some older strobes, e.g., YS200, also use capacitors in series - 600V! Very dangerous!). For modern Auto and TTL strobes: there is an SCR or IGBT in the path from the capacitor to the tube, so don't try to discharge the capacitor by applying a resistor across the tube. The commutation capacitor is used as a charge dump when a thyristor TTL or Auto strobe quenches. It is usually a high-voltage polyester type in the range 1.8 - 6.8mF. Check each capacitor with a multimeter after discharging, to ensure that the strobe is safe. You can then remove salt deposits by scrubbing with distilled water and a toothbrush. Don't re-apply power until the circuit is completely dry, and don't re-apply power if there is any blackening of the circuit board due to arcing. An arc-damaged PCB can be repaired by cutting or scraping away any traces of carbonisation and treating the exposed substrate with an insulating lacquer such as Electrolube CPL. You should allow the lacquer to outgas for ~24 hours before re-closing the housing. Arcs from HV to ground generally do not destroy semiconductors; but arcs from HV to signal, and arcs which vaporise parts of tracks, are invariably destructive. Remove all fingerprints and deposits from the tube (preferably by wiping with isopropanol) before reassembly. Dirt on the tube causes hot-spots, which may cause it to fracture in service.