Fuse blowing

[Phil Allison]

** Hi,

had one of these on the bench today:

http://www.guitar.com.au/pa_systems/phonic/images/mu1722xzoom.jpg

Basic, compact mixer with universal (90 - 260VAC) SMPS for which the
recommended AC fuse is 1 amp slo-blow.

I extracted a blown " 1A " white ceramic fuse from the IEC inlet and this
proved to be the only problem.

The AC current draw at 240V input was only 138mA, so the fuse could only
have blown due to inrush surge.

So I ran a series of switch on tests and soon saw a brief, 28 amp peak surge
on the CRO screen - which even a 1 amp slow fuse is barely able to
withstand.

These numbers make the ratio of peak surge to rms running current * 203 *
times.

Bonkers.


.... Phil

 

I call it a "nuisance trip".

Doing TVs, when the AC fuse was blown and there seemed to be no reason, I disconnected the degaussing coil and stuck a much lower value in for test. If the CRT exhibited signs of magnetisation I would replace it, replug in everything and ship it. It was a nuisance trip.

To see why, take a CRT TV, like a 32" or bigger and get the Xl and R of the degaussing coil(s) and the cold resistance of the thermistor that feeds it.. It's easy to see the thing pulls over 100 amps at startup sometimes, just for a very short time.

Start up a Sony XBR 36" CET direct view that has been sitting in a room at about 40F degrees for a day. What's that about 4C ? Pluyg that into the PTC to the coil, and then add up the dead discharged 940 uF at the recifiers. A 6.3 amp just doesn't cut it.

Each unit is different.

I also remember some RCAs that developed shorts in their degaussing coils. They tried to sell us a modification but I know how to measure shit so I found a real solution. There's did not work.

Shitty companies, all of them. At one tie they were so good, but now they want to put the servicer out of business.

Well some of us don't take too kindly to that.

 

theirs.

 

[Phil Allison]

<jurb6006@gmail.com>

I call it a "nuisance trip".


** Bullshit.

Some fucker put the wrong fuse in the clip.

You bullshitting IDIOT !!!!!!!