On 12/21/2020 3:39 AM, Don Pearce wrote:
On Sun, 20 Dec 2020 16:44:56 -0700, Paul Dorman
wrote:
This was used for a guitar amp that was continually
blowing slow-blow fuses instantly upon turning the amp
on.
https://www.youtube.com/watch?v=k5oNQ1etN2c
In my case, the bulb would briefly light up, and then
fade out within about a second. I read this meant the
amp was normal, and didn't have a short to ground, and
when I plugged the amp into the wall normally, I was able
to trouble-shoot it normally.
But I would assume the bulb lighting up initially, is due
to the initial in-rush current, that charges up the electrolytic
filtering caps, on the outputs of the rectifiers?
Because the initial 1 second flash only happened with a
linear power supply guitar amp, and did not happen with
my switched-mode guitar amp. With the latter, the bulb
never glowed noticeably, even at turn-on.
You will find that the bulb has a rather finite lifetime.Instead use
the part designed for the job, a negative temperature coefficient
(NTC) thermistor. Any switched mode power supply is most likely to
already have one fitted, which is why your bulb seems to do nothing.
While a thermistor might also prevent a fuse from blowing out,
it doesn't give you a visual sign that there is a short-to-ground in
the circuit being tested.
The light bulb turns on when there is a short to ground.