By Jed Martin
I work at a large service center for a national retail chain. Soon after I began working here, I was asked to look at some AV receivers that had a dead fluorescent display. The receivers were all from the same manufacturer, but different models. They all had one thing in common: they all used diode-capacitor voltage multipliers to take 10Vac and turn it into -25Vdc, and the capacitors in all of the receivers had exploded, and the small glass diodes were all shorted.
Upon looking up the data sheets for the diodes, I found that they were rated at 100mA forward current. A quick calculation showed that there were short 1A spikes of charging current when the receiver turned on, which settled to 80mA after the caps had charged. The fix was to replace the diodes with 1A diodes, and I wrote a tech tip and emailed it to the home audio tech support tech at the manufacturer’s service center. Within a few months, the fix was implemented as an ECO at the factory as well as a service bulletin on the manufacturer’s website.