12voltvids: Ha ha. Good for a laugh. I was thinking reversed power supply as soon as
you got the .6 volt drop. The light bulb load was one of the first things I
learned some 30 years ago when I first got into the repair business, and
the second thing I learned was to keep one hand in my pocket when working
on a live circuit. Only been bit twice, one time by an operating microwave
power supply, some 2500 volts, and the second time by 30,000 volts from a
second anode lead that was not attached properly to a picture tube by a
junior tech that changed the CRT. I was performing a convergence job, and
the lead popped off and dropped on my hand. It felt like I hit my thumb
with a hammer. Fortunately I was wearing insulated shoes, and had my other
hand in my pocket, so it just charged me up. I got almost as big a shock
when I discharged the energy in my body! Talk about a major spark from my
finger. (body charged up like a capacitor, just like static electricity
only a bigger jolt!)
Saved my life, that's for sure. Sure glad to be out of the electronics
rpcomms1: whoops a daisy classic,Ive done some like that before now I always check
12V battery leads on DVM before plugging moral of story!
tim b: i have a rally 600 watt 24 volt inverter i need to fix do you repair other
585585MC: Are you under sedation?
inventhead: by the way the lamp trick works with mosfets to i used it with tv sets
mostly p n channel out of circut
inventhead: to me thats a toy not a useful inverter i like big power transformers and
heavy duty transistors cause seeing the tiny transformers in therse units
thers no way it will out hundreds or thousands of steady watts. hi watts is
thick wire . what thay try to do is pulse that lil toy and on a scope looks
good until you add a load then the output drops and current rises . i have
a few inverters best built is a apc 24 vdc in but has a heavy transformer
iron core good 25 lbs. also keep in mind with anay inverter make sure the
feed cable is thick enough for max draw .even thicker is better than
thinner ,that will limit amps/volts and output will be poor.
inventhead: isent dc fun lol good you found the problem no transistors dont switch in
inventhead: you can use a rheostat with amp meter to, most inverters need 0ver 12
volts if the lamp cuts it down it wont start properly i did tv shop repair
over 30 yrs might i sugest look for shorted caps and mosfets fets need
to be outa circut due to resistors diodes
WECB640: Inverter takes a 15A reverse connection draw and nothing blew? Sounds like
it was built properly and not your normal run of the mill cheap junk. I say
go get a few more and use them for emergencies. Better to have a few
smaller ones than all the eggs in one basket with a large one. Good job.
reddragon27284: I'd expect to see a much larger fuse for a 400W inverter.
whiskeyify: I used to work in a tv repair shop and we used the light blub trick, if the
set had a shorted output transistor we would put a light blub in it's place
and power on the set to check the switch mode power supply. The blub might
blink, come on bright, or just glow. This is a good way to troubleshoot.
Jerry Pommer: Thanks! Sure, I can do that.
TheCrazyStudent: Cool trick, thanks for sharing. Although, I don't really see the point in
using a big lightbulb that takes up quite a lot of space on your workbench
when you can just use a power resistor with a suitable wattage rating
instead. Checking the voltage drop across that resistor will then tell
whether the circuit under test is shorted or not. Advantages: Takes less
space on your workbench and you can use almost any value of resistor you
Jerry Pommer: Thanks! It's such a useful thing when you only have one fuse left in your
tan hock jun: thanks,I have learn the light bulb trick from your video and it is a nice
video to watch :)
Donal Leader: Great video. Loved the real time thought process. Ha heard of the light
bulb trick from hams here in Ireland.
TheCrazyStudent: Very true. I was mostly referring to this situation in particular, where
you had a rather big 12V light bulb on your workbench. Finding a 12 ohms
17W wirewound resistor in ceramic case shouldn't be much of a problem, and
it will probably be much cheaper than buying a big 12V light bulb. But
regardless the method, using a current limited supply to troubleshoot a
shorted circuit is indeed a very good idea, which you demonstrated very
well here. Thanks for posting, will check your other vids too :)
Ken F: Great technique, I kept blowing a 2 amp internal fuse on my power board
from my oscilloscope even after replacing a shorted transistor. After
replacing a shorted toroidal coil I lost the ground. The light bulb
technique saved me some fuses in the process. Thanks for the informative
video and sharing your knowledge.
Jerry Pommer: Thanks! Life wasn't meant to have the rough patches edited out. Even the
dumb mistakes that others might learn something from.
Jerry Pommer: It's probably that part of the power cable that belongs to some other
device. Because you're right, to get the rated 400w out of it, you'd need
around 40 amps in!
Jerry Pommer: Thanks!
Jerry Pommer: Well, if the circuit under test is powered by 100 volts and normally draws
100 mA, but has a short somewhere that now makes it pull 1 amp, 100v * 1A =
100 watts. How big, expensive and difficult to source is that resistor?
Light bulb starts to look pretty good then. Thanks for watching!
JonathanAnon: So today's lesson is: Dont invert the power to your inverter? :-) I saw
that lightbulb trick in Jestine Yong's book. very useful.
Jerry Pommer: That's great Ken! Glad it helped.
radicalgarbage02: Didn't know about the light-bulb trick. This video was a good learning
experience. I actually like that you didn't edit too much out.
formtapez: 7.5 Amp fuse for 12 Volts (90 Watts) - Writing 800 Watt on the case - Thats
crzren: interesting.. great video!
Jerry Pommer: Yep, working in TV repair is where I learned it too.
TakeTheNarrowPath GloryIsHisName: Great video I also didn't know about the light-bulb trick A+ on that. Can
you make a more detail video on the light bulb trick thank you.