DMX-tools Quality Policy
Quality isn't just a policy; it's a way of life. Quality and low-cost are not mutually exclusive; it's cheaper to build good quality in, than to test bad quality out. The things that enhance the quality of my products also reduce manufacturing costs by reducing assembly and test labor. Conservative designs, reliable components and processes that reduce manufacturing defects save repair, rework and warranty costs and increase customer satisfaction.
Quality starts with a conservative design. Passive components are selected with tighter tolerances than needed and with higher voltage and power ratings than they will ever encounter in anything close to normal operation. This increases reliability for my customers and decreases warranty costs for me… which further benefits my customers, because warranty costs are calculated into the final selling price.
Semiconductors are selected from a list of "commodity" parts - that is, parts available from more than one manufacturer - mainly to ensure a continued supply. Commodity parts are those with a "track-record" – they’ve been around a while, proven themselves to be reliable, are sold in high volume and are unlikely to be discontinued any time soon. A side benefit is low cost, due to the competition between suppliers.
For example, the microcontroller used in the DMX-lator line is part of the 8031 family, originated in 1978. In 2003, compatible versions are available from several different manufacturers. It’s in such widespread use that, in all likelihood, more than one of those manufacturers will still be making them in 2023. In the mean time, high volumes and competition keep the price low.
Those semiconductors that deal directly with the input, output and power are also chosen to withstand unusual stresses. The venerable LM7805 voltage regulator is safe for input voltages in excess of 30 volts; in normal operation it will see 15. Even total failure of the regulation in a dimmer pack (the source of the 15 volts) is not likely to exceed the stress rating.
The LM1458 amplifier that drives the multiplex output has built-in short-circuit protection. The DMX inputs are opto-isolated for protection from ground loops, as well as static electricity. The DMX output is driven by one of three compatible chips (Maxim MAX491, Linear Technologies LTC491 or Analog Devices ADM489), all with extra ESD (static electricity) protection built-in.
Glass/epoxy circuit board material costs a few pennies more than the more-commonly used phenolic material, but it’s more resistant to heat and humidity, enhancing reliability and reducing warranty costs. A double-sided board is a little more costly that single-sided, but it eliminates the need for jumper wires (additional parts to install = more assembly labor and more chances for assembly errors). Large areas of ground plane on both sides of the board meant a little more time spent in PCB design, but reduce both emissions (the chance that the DMX-lator will interfere with some other device) and susceptibility (the chance that another device will interfere with proper operation of the DMX-lator). A parts-placement legend, silk-screened onto the board, adds a few pennies to the cost of the board, but helps reduce the chance of assembly errors and aids in troubleshooting, again reducing rework and warranty costs.
Even component orientation plays a part. All chips mounted vertically have pin 1 at the top. All chips mounted horizontally have pin 1 to the left. Electrolytic capacitors and other polarized components have the positive pin to the left. Arranging the board in this manner meant extra time in board layout, but reduces the likelihood of assembly errors (a chip or capacitor inserted backward), again reducing rework.
Prototypes were tested at extremes of temperature and humidity, shock and vibration, varying supply voltages and electrical noise before the designs were released for production. But the quality emphasis didn't stop there.
In manufacturing, the key to both low cost and high quality is repeatability. In many cases, repeatability means automation. Machines excel at doing repetitive tasks the same way every time.
In my case, the automation starts in component preparation. Radial-leaded components are manufactured with leads long enough to be used in point-to-point wiring – much longer than needed for PCB mounting.
A Hepco 1500-1 (left, below) trims the leads much more accurately (and faster) than I could do by hand.
The leads on axial-leaded components have to be both trimmed and bent to fit the PC board properly. A Streckfuss C-031(right,above) bends the leads at exactly the right place, and trims them to exactly the right length, in one fast operation.
Cutting and bending component leads is a dull,
boring job, but it requires some precision – leads too short can cause
a poor solder connection, leads too long can cause short circuits and
solder bridges. The machines never get bored and can cut and bend with
greater precision than I can by hand. They cut costs by doing it
much more quickly, too.
The mechanization continues with the actual soldering process. This is my NovaStar Spartan 7 wave-soldering machine (and me).
While I can hand-solder a DMX-lator I board in about an hour and a half (I’m very good with a
soldering iron), the machine can do it in about a minute and a half…
and it never misses a connection. It also results in a much
gentler soldering process.
The machine has a preheater that gradually raises the temperature of the whole board and all its components to near the soldering temperature. Hand-soldering raises the temperature of a single pin – the sudden temperature difference is much more likely to damage a part than is the machine’s gradual heating and cooling of the entire board.
Because of the large volume of heated solder and the fact that the board and components have been pre-heated, the actual soldering temperature can be much lower. The typical soldering iron tip is heated to 750 degrees Fahrenheit. The wave-solder process is almost 300 degrees cooler and, again because the heating is uniform, places minimal thermal stress on the components.
While most of the parts are machine-soldered, some parts, such as the address switch and the XLR connectors on the DMX-lator I, have to be hand-soldered. The switch is mounted to the back side of the board and wouldn't survive being dunked in molten solder. The connectors are just too big to go through the solder machine reliably. But switches and connectors are much less susceptible to heat damage than are semiconductors.
Once the board has been fully assembled and soldered, it is cleaned. Flux, the cleaning solution used in the solder process to ensure good connections, is mildly corrosive. If left on the board, it can gradually eat away the copper conductors, causing the board itself to fail after a few months to a few years. A clean board will last much longer.
I use an environmentally safe, water-soluble flux that washes off in warm water. Water, by itself, won’t harm an electrical component as long as there’s no power to the component. The boards don’t see power until they have been allowed to dry for at least 8 hours. Then they are calibrated, tested, installed in cabinets and re-tested before being packaged for sale.
The calibration and initial test are somewhat automated, again due to a little extra time spent in design. For example, a special test connection triggers the DMX-lator I to generate a continuous pattern of multiplex outputs corresponding to the multiplex sync level, a DMX fader position of 0 and a DMX fader position of 255 (maximum), for calibration of the multiplex output gain and offset. It then goes to a routine designed to test the address switches (switches are "moving parts" – more susceptible to failure than any of the other parts on the board). Other units have similar built-in self-test (BIST) capability.
The test connector is then removed and the board is connected to a DMX controller, a DMX effect, and a microplex dimmer pack, and is put through its paces in a simulated working environment before being passed. Again, this refers specifically to the DMX-lator I. Similar procedures, with product-specific differences, are used for the entire product line.
After the board has been installed in a cabinet, it is once again connected to the controller, dimmer pack and effect and put through its paces one last time before finally being packaged for retail sale.
There are two ongoing quality tests as well. In a Random Quality Audit, a unit will be selected from inventory, at random. The package will be opened and inspected for completeness. The unit will again be put through its paces in a repeat of the final acceptance test. Any discrepancies found will be noted and corrective action taken. The unit will then be repackaged and returned to inventory.
I do sound and lights for local-band rock concerts in my spare time. My second ongoing quality test is simply to select a unit from inventory, at random, and use it in my own concert lighting system for several shows. Again, any discrepancies will be noted and corrective action taken. When I select a new unit, the old one is cleaned, recalibrated, repackaged, and sold on eBay as "refurbished." It carries a new-equipment warranty but a much-reduced price.
The overall result is a system that allows me
to consistently deliver the highest quality products at the lowest
possible cost.