On Dec 7, 9:45 pm, "Matt J. McCullar" wrote:
Something I learned the hard way...

I was replacing a bunch of electrolytic capacitors in a video monitor. I
removed the originals all at once, taking careful notes about each location,
its reference designation, and the value and voltage of each capacitor. All
the original caps went into a zip-lock bag.

Then I got a fresh batch of new capacitors, tested each one first, and
installed them in one go. I carefully checked off each capacitor on my list
as I went. (Another tip: I colorize the top of each new electrolytic
capacitor with a red magic marker so I can readily see if I've missed
something later.)

This was about 30 capacitors. It's very easy to put one in backwards, as
you well know. I was very, very careful.

I apply power, and...

BOOM! One cap literally got blown completely out of the monitor! It sailed
past my ear and landed about three feet away! It was a small one, a 10 uF,
50 volt job, but it learned how to fly that day.

Well, poop. I quickly removed power and found the location of the fried
capacitor. I checked my notes again. Something in my gut told me to
re-double-check. I went back through the bag of original capacitors and
checked off each cap's value and voltage rating.

Now, here's the golden moment: I found my mistake. I had the right value
of capacitance, and I'd installed it correctly. My mistake was the voltage
rating. I had installed a 50-volt capacitor, which is what the original
capacitor was rated for. But... The original capacitor had some white
rubbery gunk on it; that had been applied on the circuit board at the
factory to keep parts and wiring from moving around much. It's basically a
rubberized version of hot glue. This white gunk had hardened all over one
side of this cap, and it had masked something critical: one digit. That's
all, just one digit. I removed the gunk.

The original capacitor was rated for 250 volts, not 50! No wonder the
replacement cap exploded.

So, keep this in mind the next time you're replacing a bunch of capacitors
or other electronic parts: make sure you can read ALL the numbers and
letters on them!!!

Matt J. McCullar

I always change a part or two and did the next part. Sometimes test
the unit after changing one or two parts, checking for problems caused
by new part. I don't like pulling too many parts without checking
work performed, it depends on job.