Yes, I do that quite a bit. Very similar to the trick I learned years
ago with AC-powered solid-state audio amps. Often the output and
driver transistors and other transistors will go bad by shorting out.
After replacing all the ones you think are bad, you may miss one or
two. This will probably cause a short to still present itself to the
AC line input. Instead of going through half a box of fuses and
possibly damaging more parts, use a 75 or 100 watt incandescent light
bulb in series with the 110 volts AC. If, when turning on the circuit,
the bulb glows brightly for a second and then diminishes as the power
supply capacitors charge up, everything is OK and you can remove the
bulb from the circuit. If the bulb remains fully brightly lit, you
still have a problem. I've used this technique countless times.
It wasn't clear to me what kind of capacitors were smoking. If they
were the radial-leaded type, the band is on the negative end. I've had
tantalum surface-mount caps in backwards, too. They will also get
extremely hot and smoke, or maybe even just blow off the board.
Sometimes taking part of the board with them. :-(
73, Zack W9SZ
On 9/30/13, Brad Thompson <brad.thompson@...> wrote:
> On 9/30/2013 1:58 AM, Zack Widup wrote:
>> All the surface-mount electrolytics I use must be tantalums. They all
>> have the positive side marked with a band.
> Hello, Zack and the group--
> Zack, you no doubt already know about this but some of the
> group's newcomers may not.
> If there's any doubt, connect a resistor (say, 10 ohms at 1/4 watt)
> in series with the purported positive terminal and then
> connect the series network across a power supply set to the
> capacitor's rated voltage (network plus to plus, minus to minus).
> If the capacitor and/or resistor smoke, the assumed polarity is
> For further reassurance, identify the capacitor's manufacturer and
> consult the part's data sheet.
> Your for creative smoke testing, and 73--
> Brad AA1IP