RE: Testing High voltage puck diodes.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

This is not quite the same thing, but possibly
related. I recently had a dead HD component switch. I
took it to a friend's house, who was an EE, to help me
troubleshoot it. He showed me a great trick. We both
suspected one of a handful of chips, since everything
else checked out fine. He turned it on, then hit the
first chip with a heatgun. Magically the thing sprung
to life. Excited, I took it home and looked online for
a replacement. Unfortunately it was an EEPROM. I
decided to use its 12v to power a homemade "heater"
made from a series of resistors that I glued to the
EEPROM. It now works fine.

Apparently, with many components, internal connections
can loosen, making them sensitive to heating and
cooling. Since some silicon components heat up quite a
bit, even to the point that heat sinks are required,
its quite possible that internal connections can
loosen as the various metals, silicon, and plastics
expand and contract at different rates.

Adam

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Leigh Copp"
> <Leigh.Copp@xxxxxxxxxxx>
>
> Hi Jim,
>
> In the last 20 years I've heard a lot of talk about
> diodes (and other
> devices) failing intermittently. I have yet however,
> to ever see a
> semiconductor that was anything in between good, and
> bad. They either
> fail from too much voltage, or too much current, or
> too much heat.
> Really large devices in cyclic applications,
> expecially with water
> cooling, can also fail from excessive thermal
> cycling. (Hence the
> research into silicon carbide and similar substrates
> on large power
> devices, becasue it's coefficient of thermal
> expansion is closer to
> that of silicon).
>
> I am open to the benefit of  experience from others,
> but I have spent
> literally hundreds of hours in the field
> investigating claims of
> power semiconductors that would intermittently fail,
> or only fail at
> high current or voltage. I can definitively say that
> I have yet to
> ever fail to find other problems that were directly
> responsible.
>
> High voltage passives (especially capacitors) can
> start to break down
> at higher voltages, and can appear to be fine at
> lower votlages. RF
> tank caps for example are not worth testing without
> a 15 kV hi-pot
> set; a 1000V meggohmeter hardly tickles them.
>
> Once semiconductors fail however, it is for good,
> and I have yet to
> see a failed semi that couldn't be verified with a
> DMM, although an
> analog multimeter is usually a little more foolproof
> (IE the
> venerable Simpson 260) due to its increased current
> sourcing ability.
>
> I've heard that in theory the difusion currents
> within the device
> will turn semiconductors back to beach sand if we
> wait long enough,
> but that happens at about the same speed as your
> window panes get
> thicker at the bottom (becasue glass is a super
> cooled liquid, not a
> solid), and almost as slowly as your wife's
> sparkiling rocks will
> revert to charcoal briquettes.
>
> The only thing that can go strange on you, as I
> mentioned above, is
> that the die attach on single side devices (studs
> for example)
> becomes flimsy due to thermal cycling, and the
> attendant mechanical
> fatique that it creates. This will cause the
> temperature profile to
> be less linear across the junction, and they will do
> some neat things
> when close to their limits.
>
> So for my 2.5 cents worth check them with a
> multimeter, and then install them.
>
> Cheers,
>
> Leigh
>
>
> 	-----Original Message-----
> 	From: Tesla list [mailto:tesla@xxxxxxxxxx]
> 	Sent: Sat 07/10/2006 10:18 AM
> 	To: tesla@xxxxxxxxxx
> 	Cc:
> 	Subject: Testing High voltage puck diodes.
> 	
> 	
>
> 	Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
> 	
> 	Hello All,
> 	
> 	I am preparing to install 6 sets of six series
> connected HDB7.5 puck
> 	and stud diodes in a full wave 3 phase transformer
> oil tank (given
> 	there is room once the filament transformer is
> removed). These diodes
> 	are rated at 7500 volts reverse each, with a
> forward current of 1.4
> 	amps. The recovery time is "standard". I called the
> engineering
> 	department and they said they should be fine
> without any balancing
> 	components at 60hz.
> 	
> 	Keeping in mind that these are take out surplus, I
> would like to test
> 	them under somewhat hardened conditions, not just
> the forward
> 	junction drop. I was thinking of using half of one
> of my 15KV neon
> 	transformers across a diode test setup with say a
> 30 ma load of some
> 	sort. I have a 15kv dc probe around here somewhere
> which I will also
> 	test thoroughly!
> 	
> 	What would be the wisdom of noting the waveforms of
> each diode and
> 	discarding the ones that are inconsistent?
> Naturally I will test the
> 	diodes with a meter first. Anyone know a better or
> safer way to do this?
> 	
> 	Thanks in Advance,
> 	
> 	Jim Mora
> 	
> 	There are a lot of bolts holding on the
> transformer/PS cover! And I
> 	would not like playing with these pucks once
> submerged!
> 	
>