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Old 3rd July 2008, 03:51 PM   #1
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Default Warning: breadboard setup, no fuse and non stop operation...

Hello

Yesterday night I had very big luck, not causing an incident in my apartement.

At four a clock I woke up by a very loud hum out of my living room.

Behind a furniture I realized smoke and quickly unplugged the main plug.

What happened?

I have a breadboard setup of a stereo LM3886 amp with OPA buffer.

I am using one channel of this breadboard since some months as subwoofer amp. The amp was 24h under power.

No fuse between tranny and board.

During the night, one cable made contact to the back of a MUR860 diode. The diodes melted down and I woke up...

A curtain was 3 cm away.

What, if this happened during my absence?

Please mothers, tell your children not to do what I have done!

Click the image to open in full size.

Click the image to open in full size.

Franz
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Old 3rd July 2008, 03:59 PM   #2
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You were lucky! I keep everything on power strips and if I'm not around or asleep, the power strips are off. I keep a lamp plugged into the same strip so I can instantly tell if I've left it on. Just because you're paranoid doesn't mean they're not after you.
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Old 3rd July 2008, 04:11 PM   #3
kevinkr is offline kevinkr  United States
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Wow, close call Franz.. Something I worry about constantly... Like Conrad I do keep a lot of stuff on strips, fuse everything, and try to remember to turn things off! (Sometimes I forget)

I package up everything before I put it into continuous or semi-attended use, metal boxes provide some measure of protection.

Properly sized fuse or circuit breaker is mandatory..

Thanks for posting this timely warning here, and I am glad that nothing worse happened. Look at it as a lucky wake up call..
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Old 3rd July 2008, 04:18 PM   #4
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Thanks Kevin

I should be ashamed, to show this pictures, but like you said:

Take it as a wake up call.

And I want to share this experience with as many people as possible.

Franz
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Old 3rd July 2008, 04:21 PM   #5
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no comment

Click the image to open in full size.
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Old 3rd July 2008, 05:37 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Franz Gysi
Thanks Kevin

I should be ashamed, to show this pictures, but like you said:

Take it as a wake up call.

And I want to share this experience with as many people as possible.

Franz
I think most of us have had similar moments, and I think if this provides a timely warning to someone else then I think it is good to share it.

Many of my comments about catastrophic events comes directly from my own personal experience, and some of them were the direct consequence of mistakes I made and others were random unforeseen events. Here no actual harm came to anything but the pcb, some wire, and a few parts. A fortunate learning experience I guess.

The thing that sticks in my mind over 30yrs was the exploding 50V electrolytic inches from my face. I've never seen anything like it since, like a small cannon belching flame and shooting paper confetti everywhere - it was a CDE axial type.. (Had the debris hit my face I might have been injured - I was wearing safety glasses though.) Running at 70% of rated voltage in a cool environment, I smelled it just before it went. I was doing some measurements on a project amplifier (early mosfet) I had just completed and the cap exploded, sheared the body off of a nearby driver transistor which resulted in a cascade of failing power mosfets in the output stage and the darlingtons in the series pass regulators. The fuse never blew! And there probably wasn't anything I could have done to prevent it. Worst of all, after all of that effort that amplifier just didn't sound good.
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Old 3rd July 2008, 05:51 PM   #7
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Quote:
Originally posted by kevinkr


The thing that sticks in my mind over 30yrs was the exploding 50V electrolytic inches from my face. I've never seen anything like it since, like a small cannon belching flame and shooting paper confetti everywhere - it was a CDE axial type.. (Had the debris hit my face I might have been injured - I was wearing safety glasses though.) Running at 70% of rated voltage in a cool environment, I smelled it just before it went.

I had a "similar" experience about the same time with something supposedly much less dangerous than an electrolytic. I somhow connected an 741 wrong (no overvoltage or so, but maybe I reversed the supply pins). Bang, and piece of plastic hit my face. Fortunately it didn't hit my eyes. I had no glasses of any kind. The IC didn't melt or anything like it. It just launched a missile in the form of a single piece of cone shaped plastic, leaving a crater so I could see the chip at the bottom.
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Old 4th July 2008, 11:27 PM   #8
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You're a lucky man!

I agree,post the pics as an example to others.
Don't feel bad,we've all done similar things!


I absolutely hate exploding caps. Every time I power up an 'unknown' piece of equipment,I always make sure to keep clear,and maybe even turn/tilt the piece a bit,so the caps aren't facing me!


I can't even count how many transistors and IC's I've exploded..
I hate getting hot plastic and silicon in the face.
(Wear safety glasses people!)
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Old 5th July 2008, 09:15 PM   #9
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Default Safety first

Hi Franz,

Thanks for sharing these pics it will probably help others.

My daily job is a safety engineer where we blow up stuff all day long to make sure that when people buy any mains powered equipment it does not catch on fire, etc. Compliance to A/V stds are very strict and 50% of time any product must be re-designed or protection added and this goes also for High-end stuff costing mega money.

Always use certified components like switch, fuses or breaker and if you do not know what you are doing with mains (120Vac, 230Vac) please do not touch it or ask for guidance. This is a great hobby but it must be done the proper way.

Always fuse the primary (between mains and tranny) and from tranny to amplifier.

Please be safe and enjoy the music

Regards,
Eric
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Old 14th July 2008, 02:42 PM   #10
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Finally

Click the image to open in full size.

The amplifier got it's enclosure (the material was ready for more than one year).

The enclosure is a aluminium chassis, formerly intended for a never realized pre-amp. Two walnut sidepanels (more than 150 years old, from an old bed), to carbonfibre sticks between the sidepanels and a grid over all.

Under the chassis a big torroid tranny, above the chassis the amplifier.

Of course, there is now

- a main switch
- a main fuse (3A slow)
- two secondary fuses (2A slow)

And my whole hifi setup is now connected to one mains connector with a switch, to completely switch it off when out of use.

There is no need for a volume control, as I use it as a subwoofer amp, controlled by an active xover. The amp inside is a stereo board, even when I use actually just one channel. The plan is to use later a bridged setup, but actually I drive two subs in parallel, so only 4 ohm. In a bridged setup, this would result in 2 ohm only per amplifier.

Regards
Franz

/Edit
Repairing the damage I recognized the epoxy from the board was completely gone under one diode! The glass fibre was free on the air.
I just replaced the four diodes and had to replace a 7815 regulator who did not like the AC (psu for the buffer OPA).
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