Need help troubleshooting Series 2 TiVo

On 2008-04-01, w_tom wrote:

5 and 12 volts on a Tivo motherboard will not electrocute. Others
who deny this are simply hyping fear based in the same reasoning that
is also called junk science.

"Junk science". Man, I knew I recognized this cat's "style". Not hard to
miss, even after about 3 years.

On Mar 31, 4:47*pm, (Scott Lurndal) wrote:

*How
many of us work where electronics are designed and built?

*Electrocution from 5 and 12 volts is ridiculous - hyped fear. One

While the current in a TIVO will be limited at 5v and 12v, I've seen
5v supplies that can fry the unwary installed in large computers,
complete with 2 inch square aluminum bus-bars. *

That same TIVO case also has mains current internally that is much more
hazardous.

My bad on the electrocution comment. It would be unusual to get
shocked from +5 or +12V, this was not what I was referring to. My
recollection from years ago when I opened my tivo is that the power
supply was open frame, i.e. you could touch all the parts. If you try
to put an 'ice pack' on something I'm guessing there will be water
everywhere from condensation, and I would be wary of even consensed
water on the high voltage.

The safety agencies do require special consideration for low voltages
(50V) that have more then 240 volt amps of capacity (the tivo power
does not). You can still get shocked on these lower voltages. If you
doubt this, try touching your toungue to both terminals of a 9V
battery. In the case of those 5 volt 2" square busbars, these are
perfectly safe to touch under all but the rarest of conditions. The
main risk here is the use of jewelry. At low voltages, the busses can
be routed very close to each other, having your wedding ring caught
between a 2 volt 2000 Amp bus will not electrocute you, but you will
never forget it wither. Current through the heart is what causes
death, it only takes tens of milliamps. This is set by first having a
path through the heart, then the driving voltage, and the total path
resistance, which is normally dictated by contact surface resistance
(this is why dry is good).

On Tue, 1 Apr 2008 05:07:14 -0700 (PDT), wrote:
If you try
to put an 'ice pack' on something I'm guessing there will be water
everywhere from condensation, and I would be wary of even consensed
water on the high voltage.

Try an experiment. Put an ice cube in a zip-close plastic bag. Leave it
on your kitchen counter for five minutes. See how much condensation is
on the counter when you pick it up. Now remember that you're probably
NOT heat-testing the power supply, OR the hard drive, but instead things
like RAM, GPUs, CPU, etc. Note how wet your fingers are picking up that
bag by the corner above the ice. Go watch the "Third Rail" episode of
MythBusters. Still think you're in danger for your life?

The safety agencies do require special consideration for low voltages
(50V) that have more then 240 volt amps of capacity (the tivo power
does not). You can still get shocked on these lower voltages. If you
doubt this, try touching your toungue to both terminals of a 9V
battery.

Quit licking your tivo. Wet your finger. Put it across the same battery.
Doesn't feel nearly the same, does it? That's SCIENCE, it is!

In the case of those 5 volt 2" square busbars, these are
perfectly safe to touch under all but the rarest of conditions. The
main risk here is the use of jewelry. At low voltages, the busses can
be routed very close to each other, having your wedding ring caught
between a 2 volt 2000 Amp bus will not electrocute you, but you will
never forget it wither. Current through the heart is what causes
death, it only takes tens of milliamps. This is set by first having a
path through the heart, then the driving voltage, and the total path
resistance, which is normally dictated by contact surface resistance
(this is why dry is good).

So don't work on your tivo naked sitting on a metal stool in your
backyard. Where does that ground path come from when you're dressed,
wearing socks, shoes, standing on rubber-backed plush carpeting? Go
measure the resistance between even your wet wet hands[1] and some handy
ground point. Even between your wet hands you'll probably see several
hundred thousand ohms. 12v / 100000 ohms = 0.12 mA, well below the
common understanding of 10-15 mA to cause muscle spasm, and 50-100 mA
that might trigger heart fibrilation (but that want AC, btw...).

Short answer is that you're far more likely to blow something in your
tivo with a static charge touching something dry than elecrocuting
yuourself with a droplet of condensation.

[1] I get a measurement of 500,000 ohms between wet hands. 1,200,000
ohms with driy-ish hands, To get the 100,000 used in the example you
might have to stab yourself with the probes.

--
2. My ventilation ducts will be too small to crawl through.
--Peter Anspach's list of things to do as an Evil Overlord

In article , w_tom wrote:
On Mar 29, 3:37 pm, wrote:
Where did you get the information that 140F is an ideal temperature
for a disk?

Do you read manufacturer datasheets before posting? I do for more
than two generations. Posted are techniques for finding a problem
before fixing it - that contradicts the many popular myths from those
who never even read datasheets.

What happens if water gets between IC pins? If circuit does stop
operating (obviously without damage), then simply power off, dry
everything, and continue diagnostics. BTW, how do we clean newly
built electronic boards. Wash them in a dishwasher with water. How
many of us work where electronics are designed and built?


That would be ME!!! for 4 years.
http://www.dod.com/

Then 5 years at
www.spectrasymbol.com

1 year at a custom battery dealer making battery packs.


Electrocution from 5 and 12 volts is ridiculous - hyped fear. One
intentionally confuses 120 VAC on a hair dryer with 5 VDC on a
motherboard. He hypes fear based in technical naivety. Voltage below
50 V are quite safe. Those motherboard voltages cannot push dangerous
currents.

Those who don't learn technology and don't read data sheets may also
want to cure symptoms with 'more fans'. Instead, heat is an effective
diagnostic tool; not something to cure in that Tivo. "It could be this
or could be that" does not help the OP. Provide are diagnostic
techniques to find that problem. Heat is a diagnostic tool Voltage
measurements are a diagnostic tool that provide numbers. Numbers that
can elicit new information from the better informed posters who also
read datasheets.

Arrogant little ****s aren't we?

In article , w_tom wrote:
On Mar 31, 3:47 pm, (Scott Lurndal) wrote:
Why "obviously without damage"?

Obviously, when one has experience and knowledge of digital
electronics even dating back to DTL and TTL. Obviously no damage. If
water causes operational problems, simply shut down, dry, and
repower. Meanwhile, cooling is another good diagnostic tool to find a
temperature sensitive defect - to identify the suspect before fixing
anything.

Disk drives work fine even at 140 degrees F. We discover defective
hardware by using diagnostics such as heat. If hardware fails when
heated even with somethng so cool like a hair dryer, then that
hardware is completely defective. Heat is a diagnostic tool. If a
disk drive does not work at 140 degrees F, then that disk drive has
been identified as defective.

5 and 12 volts on a Tivo motherboard will not electrocute. Others
who deny this are simply hyping fear based in the same reasoning that
is also called junk science.

Provided are techniques to locate a failure.
No, those two voltages wont kill you but put one finger on that mains lead of
the switching power supply, or many of the parts of the supply and it will
knock you to the ground, and can kill you.


BTW, you come across as a dweeb!

We can agree to disagree on what we each think is safe. I do however
have some suggestions for you.

1) Make a distinction between entertainment (Mythbusters) and science
2) Spend 10 minutes learning about how shock occurs (
http://en.wikipedia.org/wiki/Electri...ting_lethality
, no doubt many others).
3) Put a new battery in your meter

On Wed, 2 Apr 2008 04:14:59 -0700 (PDT), wrote:
We can agree to disagree on what we each think is safe. I do however
have some suggestions for you.

1) Make a distinction between entertainment (Mythbusters) and science

I do that. I like retesting the stuff they do that I can. It's fun.
Most of their problem come down to erring on the side of dramatic
results

2) Spend 10 minutes learning about how shock occurs (
http://en.wikipedia.org/wiki/Electri...ting_lethality
, no doubt many others).

Did that, including the discussion page, and reviewed prior to posting.
The other experimental results listed on the discussion page support
my conclusions well, by indicating higher measurement for human
resistance, and calling out problems with the main article text that
would exaggerate lethality with regard to fibrillation.

3) Put a new battery in your meter

Regularly.

--
Windows is a pane in the ass....

On Apr 2, 6:14 am, wrote:
We can agree to disagree on what we each think is safe.

Meanwhile, industry standards consider voltages under 50 as safe.
Even the Wikipedia article states same. Tivo motherboard voltage is
below 13 volts. Why did anyone hype fear about lethal voltages where
none exist and where that fear is completely irrelevant? Amazing how
the OP's question on a Tivo problem gets subverted by those with so
little grasp as to believe Tivo motherboards are lethal or that
dampness will destroy semiconductors.

Provided were diagnostic techniques to find a Tivo defect.
Hairdryer on highest heat or icepacks use completely normal
temperature extremes to isolate a defect. Also recommended were
numbers from a multimeter. An opened Tivo will not overheat. An open
Tivo in a 70 degree room that claims to overheat would more likely
have defective heat sensors. Those would probably be on motherboard -
where no lethal voltages exist.

w_tom writes:
On Apr 2, 6:14 am, wrote:
We can agree to disagree on what we each think is safe.

Meanwhile, industry standards consider voltages under 50 as safe.

It's already been pointed out to you at least three times that the
TIVO power supply is fed from mains voltages (NA 120V, ROW 240V),
which can be quite hazardous. Thus, if you open up your TIVO and stick
an icepack in there somewhere, there is a non-zero probability
of electrocution hazard from the mains side.

scott

On Apr 2, 7:51 pm, (Scott Lurndal) wrote:
It's already been pointed out to you at least three times that the
TIVO power supply is fed from mains voltages (NA 120V, ROW 240V),
which can be quite hazardous.

Do you read or just assume what I posted? A power supply designed
to operate from 120V, 240V, or even 2,000V makes no difference to
voltages on a motherboard. As required by a power supply - it makes
all exposed motherboard voltages irrelevant.

Did you read what was previously posted or just post a fear based in
rumor? Scott who read and understood this would not be posting. What
he did not grasp is posted again ... for a third time:
Do not use a finger to find hot parts on a power
supply since that supply will have 300 volt charges
on some parts and that voltage is sometimes even
on heatsinks.

Using an ice pack to isolate failures on a motherboard is not
hazardous. Any water from that icepack will not harm motherboard
electronics. Why will water not harm motherboard electronics?
Obvious if using basic electronics knowledge. Why does a power supply
make AC mains voltages completely irrelevant on a motherboard? Again,
first required is basic electrical knowledge..

If voltages on a motherboard are so hazardous, then Scott's post
should have said, "Never ever remove the cover on a Tivo because
hazardous voltages can exist even when the AC power cord is not
connected." Did Scott know of hazardous voltages can exist even
without an AC power connection? Aagin iIrrelevant since:
Do not use a finger to find hot parts on a power
supply since that supply will have 300 volt charges

Common knowledge now posted a fourth time. Same basic knowledge
that also makes obvious "no hazardous voltages exist on a
motherboard".

Amazing how many have posted fears without learning the basics.
Scott did not read disk drive datasheets to somehow know 140 degrees
must be destructive. Scott did not have basic electronics knowledge
to know why water would not cause digital electronics harm - even to
digital electronics of 1960s vintge. And again, Scott somehow knows
hazardous voltages must exist on a motheboard.

Scott demonstrateds why more than 50% of employees in the Silicon
Valley are now immigrants. Too many somehow know - do not understand
how to first learn basic facts. No wonder so many blindly believed
Saddam had WMDs. It was rumored to be true. Therefore it must be a
fact. Just another reason why military academies don't want
communication majors; instead graduate everyone with engineering
training - so as to grasp reality.