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On 27/01/2011 17:41, Terrance wrote:

"Plexiglas" is PMMA...Poly(methyl methacrylate)

It's exactly the same as Lucite.

And Perspex, here in the UK. It used to be made by ICI but I don't know
if they are still around.

Leon
--
Leon Heller
G1HSM

I am working on my project. Although I want to make a USB I/O device, I
have realized I just don't have the confidence for it. So I have decided
to buy a USB I/O device and get on with things. I will come back to this
later once I am done more of the project.

So I am trying to find Criteria for the USB device. At the current time
my list is:

Must have Linux drivers (accessible from Java).
Must have Pulse Width Modulation (probably two per device).
Reversible ports would be good Input or output on each pin.
Should have at least 16 ports.
It would be nice if you could time ports to flip on for a short period
(to not burn out solenoids).

It would be used for:
Turning on and off lights. (I think 9V bulbs. Might be 12V).
Sense switches closing.
Firing Solenoids at 48V for short periods so they don't burn out
Holding Solenoids via PWM to keep them fired but not burn them out.
For 48V I am looking to get a power supply and then use a power transistor.

I have looked over the internet and I have found tons of boards that
fit. But I have no experience on which one to choose or what is the
"best board". I am in Toronto ON Can so if there is a supplier there
that would be great.

Just curious, did you unload all your discs before taking it in? Did you save all your disc packaging?

Mark

Sent from my iPhone.

On Jan 27, 2011, at 1:42 AM, "Randy" <solargasfarts@...> wrote:

Has been looking for SIMPLE way to reverse hobby DC motors to reverse tank or ship turret once mechanical triggered (like by a contact switch). Has to be very simple because it is for tiny scale models :)

"Plexiglas" is PMMA...Poly(methyl methacrylate)

It's exactly the same as Lucite.

-Terrance

--- In Electronics_101@...
<mailto:Electronics_101%40yahoogroups.com>, "Roland F. Harriston"
<rolohar@...> wrote:

If I recall correctly, "plexiglass" is an old trade name that DuPont
Corp. used for their version
of a particular acrylic material. Every plastics manufacturer had a
trade name for their various products.

So, first you must know exactly the generic or technical name for the
material you are working with.
Then, you can find the correct adhesive for that particular material,
and how to cut, mold and/or
machine that material.

You can Google the trade name of the material you want to work with,

and

then find the correct
methodologies for working with that material

All of these "plastics" ...whatever they are called commercially, are
specific polyresin formulations,
each requiring different working techniques.

There is no "one adhesive fits all" situation. If you use the wrong
technology with a particular
material, you wind up with a ugly, unstable, cracked and warped mess.

Roland F. Harriston, P.D.
****



vaclav_sal wrote:

I would like to use plexiglass as my project enclosure (so everybody
can see my messy design!)

My questions:
What to use for gluing. Superglue leaves nasty residue film on
everyting and if not accessible it looks crappy.
(So what if they use it to get fingerprints.)
It needs to be strong, fast drying and absolutely invisible.

How do you polish plexiglass? ( The cut edges need to be polished)
I recall using toothpaste, but there must be something made

specificly

for plexi.
Thanks for reading.
Vaclav AA7EJ

If I recall correctly, "plexiglass" is an old trade name that DuPont
Corp. used for their version
of a particular acrylic material. Every plastics manufacturer had a
trade name for their various products.

So, first you must know exactly the generic or technical name for the
material you are working with.
Then, you can find the correct adhesive for that particular material,
and how to cut, mold and/or
machine that material.

You can Google the trade name of the material you want to work with, and
then find the correct
methodologies for working with that material

All of these "plastics" ...whatever they are called commercially, are
specific polyresin formulations,
each requiring different working techniques.

There is no "one adhesive fits all" situation. If you use the wrong
technology with a particular
material, you wind up with a ugly, unstable, cracked and warped mess.

Roland F. Harriston, P.D.
****



vaclav_sal wrote:

I would like to use plexiglass as my project enclosure (so everybody
can see my messy design!)

My questions:
What to use for gluing. Superglue leaves nasty residue film on
everyting and if not accessible it looks crappy.
(So what if they use it to get fingerprints.)
It needs to be strong, fast drying and absolutely invisible.

How do you polish plexiglass? ( The cut edges need to be polished)
I recall using toothpaste, but there must be something made specificly
for plexi.
Thanks for reading.
Vaclav AA7EJ

I don't know what the failure mechanism might be. My conclusions aren't set
in stone, nor were they reached very scientifically.

Maybe the real problem is that if you replace caps in existing equipment
with higher voltage rating caps, they are larger and that puts them closer
to heat producing components around them and slows airflow patterns,
overheating the caps and causing early failure.

BTW, if that 400V rated aluminum electrolytic cap self-regulates down to
25V, the capacitance is going to change as the dielectric oxide layer gets
thinner. And I'd not count on it being the same thickness all over.

We disagree on whether or not ESD can do hidden damage to equipment, too.
And there is a lot of proof of that.

years ago when I had a computer store I contacted Sony corporate re repairs on
a monitor that had been sent in for repairs over 6 months before. I asked them
to return the unit unrepaired so I could place it in my store window with a sign
telling why I couldnt in all conscience sell Sony monitors anymore. My customer
had a free upgrade to a bigger better monitor within a week.
Some companies just build stuff. A friend of mine who had toured Sony in Japan
said if a board failed they didnt repair it - they crushed it. They dont even
repair their own stuff they just build another. Our throwaway society
Kirk

________________________________
From: Mark Tolleson <mark1200sportyrider@... <mailto:mark1200sportyrider%40yahoo.com>>
To: "Electronics_101@... <mailto:Electronics_101%40yahoogroups.com>" <Electronics_101@... <mailto:Electronics_101%40yahoogroups.com>>
Sent: Thu, January 27, 2011 6:30:07 AM
Subject: Re: [Electronics_101] Sony replacement parts


Just curious, did you unload all your discs before taking it in? Did you save
all your disc packaging?

Mark

Sent from my iPhone.

On Jan 27, 2011, at 1:42 AM, "Randy" <solargasfarts@... <mailto:solargasfarts%40yahoo.com>> wrote:

I have a Sony 400 disc DVD changer model DVP-CX995V. My repair man

says it

needs the laser assembly and it has now been at his shop for over

eight months.

He is not a ripoff guy, he used to live in my apartment building and

was friends

with everyone and his shop is in good standing with the Better

Business Bureau.

His parts supplier did verify receiving his parts request, so, I am

wondering if

anyone can shed some light as to why it is taking so long to get the

Sony part

that he needs.

Thanks.
Randy

That's just not plausible. The dielectric layer will always be sufficient
for the applied voltage, it is a self regulating process. It might not be
sufficient for the rated voltage if operated for very extended periods very
much below it, same as if it was stored without any voltage, but even that
condition can be rectified by reforming. There is just no mechanism that
causes a capacitor to fail sooner if operated at lower voltage. Just the
opposite, if you use a 400V capacitor in place of say a 25V one it will last
much much longer simply because the can is physically much larger which
always leads to a higher lifetime. I regularly replace capacitors in old
test gear with the largest can size that can be accommodated, which means a
higher voltage rating at the same capacity.

There might be things tech learn through experience, but there might
actually be things the capacitor manufacturers know for sure and techs may
just have misinterpreted.

Anyway this whole reforming issue isn't of all that much importance unless
you are dealing with decades old equipment. Even then it is usually not
needed. Only very old gear (with linear supplies) may be powered up with a
variac, and even there are dangers such as overloading components with the
low input voltage, regulator valves for example.
The jury is divided over the idea, and the only undisputed way to reform
capacitors in such situations is by feeding the internal supply rails with
external current limited supplies. Not worth worrying about in all but the
most exceptional circumstances.

ST


On Wed, Jan 26, 2011 at 11:08 PM, AlienRelics <alienrelics@...> wrote:

Running an aluminum electrolytic capacitor at well under its rated voltage
will cause the oxide layer to not reform correctly and the leakage current
may rise. Then the heat can cause pressure that causes leaks around the
seals, drying out the electrolyte.

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