Last update 10/8/07

The information provided here is only the most basic safe practices for assembling and testing electronics. Electronics cannot be learned overnight, and testing/trouble shooting takes years to become proficient at. Most people I know who do this for a living (including myself) find the learning process is never ending. The comments below are some of the most common mistakes, but in no way cover every possible act of carelessness (only the ones I have done). When AC voltage is used (in the case of both the HVTP2 and HJFP2 kits), there is inherent risk. Line voltage can kill, though it typically just hurts like hell. The biggest danger is when electricity flows through you, say from one hand to the other, or from a hand through your body and out your feet. The HVPT2 kit has the added hazard of a high voltage power supply for the audio circuit. A good zap from a hi voltage supply can send you across the room, as it makes every muscles in the current path flex very quickly, and harder than your body normally can. I have been tossed out of my chair a couple times in my life working on guitar amps. Are you scared yet? Hopefully enough to read and follow the practices below.

NEVER MAKE CONTACT WITH LIVE CIRCUITS, USE ISOLATED PROBES

Never ever use a metal object to probe a circuit. Most meters come with isolated probes. I use "micro grab" test leads, they have a small clip at the end that is spring loaded, so it latches onto a component lead. The exposed metal at the end is very small, which makes it difficult to short something out. The standard probes provided with most meters have a long exposed metal shaft, which can easily make contact between two circuit points. If you have this type, cover all but the very tip with electrical tape. Do not use alligator clips, they are physically large, and tend to pop off, potentially shorting something out.

TEST USING ONE HAND, KEEP THE OTHER BEHIND YOUR BACK

This is an old electrician rule when working on live circuits. As a rule, you put one hand behind your back so you don’t become a current path, in the event you accidentally touch something. What often happens is you are holding the chassis (which is ground), or your arm might be in contact with it, and then you touch a live circuit with your other hand, and presto you are a circuit path. The one hand rule minimizes the danger, but is only part of the picture.

WEAR RUBBER SHOES, WORK ON A RUBBER MAT, DON’T TEST IN A WET ENVIRONMENT

Just as getting both hands into live circuitry can create a current path, your feet are also a potential circuit path, as well as your butt in your chair. Leather shoes or sandals are fairly good conductors, and are not acceptable. Rubber sneakers provide better insulation, and are preferred. In addition, if you have a rubber floor mat, that provides another layer of insulation. The idea is you are trying to increase your resistance value (yes you are a resistor, take your ohm meter and hold the probes in each hand), the higher the value of resistance you are, the less current can flow through you. Moisture makes your resistance drop extremely low, so if you are working in a hot environment and sweating, the hazard is greatly increased. Never test electronics if there is any moisture present in your work area (especially on the floor) or if your shoes are wet. Water is a great conductor, salt water is better.

ALWAYS UNPLUG THE AC POWER BEFORE WORKING ON ELECTRONICS.

During test/trouble shooting, you may find you have to turn the power off, solder something, and then bring the power back on. Although the power switch is off, there is still AC on the power entry module, fuse, and power switch. ALWAYS disconnect the cord from the power entry module before working on the unit, even if the power is off.

MAKE CERTAIN LARGE ELECTROLYTIC CAPS ARE DISCHARGED

Capacitors store charge, and can hold it for days if a current path is not present to bleed it off. This charge is typically what shocks people in circuits that have been shut off, the classic is guitar amps. Under normal circumstances, the circuits attached to the power supply will bleed the charge off to a safe level after a minute or two (or less). The problem is if something is wired wrong, or blown and not pulling current, the power supply isn’t seeing any load, and as a result may stay charged up longer. The easiest thing to do is monitor the DC voltage on the large electrolytic caps connected to the bridge rectifiers in the psu after you have turned off the power, and removed the AC line voltage to the chassis. This is especially important in the HVTP2 hi voltage supply. Never short an electrolytic cap to discharge it, this will damage them.

SAFE ASSEMBLY NOTES

The circuits you are building require soldering. You should avoid breathing the fumes from solder, and work in a ventilated area. Also most types of solder contain lead, so you should always wash your hands after handling it. Never eat or smoke while you are soldering. I use Kester SAF-A-LLOY #58/245 .031, it is a lead-free silver based solder available from Digikey. Read the precautions printed on the solder you are using for details. If you have concerns, the safest thing to do is wear a respirator designed for painting (not the paper particle masks which do nothing for fumes). You should always gear safety glasses, to prevent a "solder splash" from getting in your eyes. Molten solder is at roughly 700 degree Fahrenheit, and can seriously damage you eyes if it were to get in them. This typically happens when something you are soldering (mostly point-point) has tension on it, and springs loose when the soldering iron makes contact transferring heat. The spring action can launch a molten fragment of solder into you face/eye. The soldering iron is very hot and can cause 3^rd degree burns if it comes in contact with your skin long enough. Never touch the tip of a heated soldering iron.

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