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Old 26th November 2006, 06:20 PM   #1
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Default If it aint broke

Don't fix it! Words from my Dad from years ago that I did not head. 30 minutes ago I had a perfectly fine adcom 555, I thought, "I'll just check the bias".
Shorted form the TP to either a transistor case or the supply fuse right next to it, and poof.

Damn.

Just a mild vent, sorry.
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Old 26th November 2006, 06:29 PM   #2
poynton is offline poynton  United Kingdom
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Yes, many times !!!!

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Measure twice, cut once !

Of course, the power is off !


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Old 26th November 2006, 08:34 PM   #3
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Default I am very sorry about your tragedy my friend...i ensure that many of us had

lived the same experience you are leaving.... very bad the feeling.

Not only me, but our forum friends will help you if needed and asked.

You are not the one..... not the last.... this happened to all of us...but only few guys had the courage to tell.

My Dad also told me not to get married...i made the foolish twice, and going to third moment of severe insanity....that's life..we are humans.

regards,

Carlos
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Old 26th November 2006, 08:38 PM   #4
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Old 26th November 2006, 08:49 PM   #5
lineup is offline lineup  Sweden
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normal multimeter probe tip
can be 1 mm in diameter
and have ~10 mm length without isolation

to try and avoid such shorting with the probe
we could put some isolation cover onto tip
- you can use for example plastic pieces - leftovers
from when you have done un-insulating of PVC isolated 1 mm wires

also we can sharpen the probe tip
until it looks like needle
and only like 1-2 mm of this thin, sharp probe tip is sticking out
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Old 26th November 2006, 09:17 PM   #6
kvholio is offline kvholio  Netherlands
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You can also avoid using the probe, but then you loose a hobby.
We all have experienced this, thats why we're here.
For me , it has been a while, but a few months ago i looked at caps that looked like caulyflowers.
Stupid mestake, reversed polarity.

Klaas
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Old 26th November 2006, 09:28 PM   #7
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I slipped with the meter probe while measuring the bias on my first Sansui amp,right after repairing it...

Blew it up..
Fixed it..
Blew it up again..




We feel your pain.
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Old 26th November 2006, 09:39 PM   #8
jleaman is offline jleaman  Belgium
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I've done this too Working on a sony amp that tooke me 4 months to get the transistor's went to check the rail voltage and blew up the amp again. I then threw it out. Of course keeping some parts.
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Old 26th November 2006, 10:08 PM   #9
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Thanks guys!
Since I was running in a bridges mode I think it might in a weird way mitigated some damage. I re-fused it, and powered it through a 40 watt bulb. The yellow distortion lamp lit up, and got 31 volts positive DC at the output.
The funny part is I was "playing" with the negative board where I smoked it. So far I found (on the positive board) the driver transistor shorted out, with about 28 ohms resistance.
That would be the 2sc2344 acording to the schematic.
Do you think I have to dig further? Would this transistor throw a spear into the front end?
Just seems weird that this particular one blew, I would have thought it would be atleast on the "negative" output board.
The left channel seems fine, so I guess I ought to count my lucky stars!
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Old 27th November 2006, 12:34 PM   #10
NH TomG is offline NH TomG  United States
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Default I pulled a similar bonehead move

last week on a Citation 16 while checking emitter voltage. The amp has a small vent on top of the output stage, and I removed it to check the aforementioned emitter voltage... thought it was powered off, but it was not. Shorted the emitter of one of the outputs to ground, fried the device, which was an original RCA 1B05. It is now getting a full set of On Semi MJ15024G's purchased from Allied. Oh well- I feel your pain.
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