Toshiba TV29C90 problem; Image fades to black...

[ggulden]

Hi Dave,
Did replacing the main IC on the U board fix this problem? I have the
exact same TV, even the year and it is showing the same problem.
Greg

 

[NSM]

"Roger Johansson" <no-email@home.se> wrote in message
news:Xns95CD3034DC28386336@130.133.1.4...

| The reality is that most of the experts here are old and rich and very
| knowledgeble people who enjoy writing explanations, old engineers and
| writers of technical books. Such people have no need for small sums of
| money, less than 10000 dollars won't even get them off their chairs. It
| doesn't mean anything to people who have already made millions working
| for NASA, are responsible for the circuits inside every PC, are owning
| their own factories or are old authors of books and electronics magazine
| articles.

And the rest of us have all lost money on one-offs for non-commercial
persons - sometimes more than once.

N

 

[Fred McKenzie]

<< And is "bad thermostat" a good diagnosis? >>

Matt-

I suggest you take the make and model number to a place that sells appliance
parts. They should have microfilm of parts breakdowns for most appliances,
sometimes including wiring diagrams.

A thermostat is the most likely cause. However, if your oven uses an
electronic circuit, it may have a temperature sensor, possibly a thermistor.
Temperature control could be accomplished by switching triacs that connect the
heating elements.

Whether it uses a thermostat or a thermistor, the sensor could have been moved
to a place where it isn't exposed to the hot airflow. There might also be some
debris blocking airflow in the area of the sensor.

Fred

 

[Rich Grise]

On Mon, 27 Dec 2004 22:02:20 +0000, Guy Macon wrote:

John Woodgate wrote:

It is pretty simple, but for one thing - it's very difficult if not
impossible to get technical information on boom-box circuitry unless
it's an up-market product and you are an authorised dealer, and such
information is almost certainly necessary.

It sounds to me as if you could do it simply by accessing the
microphone, speaker, and switches - no knowledge of the internals
needed.

Someone else mentioned having engineers and/or tech examine the box
for spoofs - in that case, you'd have to get one with one main processor,
and rewrite the ROM.

Cheers!
Rich

 

[NSM]

"Ed Price" <edprice@cox.net> wrote in message
news:%56Ad.14843$8e5.12158@fed1read07...

| Do you know that owning 12.5% of something that goes bankrupt is not the
| road to riches? <g>

Buy Bre-X at 0.25 and sell at $280 -- happiness.

Buy Bre-X at $280 and sell at 0.25 -- misery.

It's all about when!

N

 

[Guy Macon]

WilliamP.N.Smith wrote:

Of course, there's always the sleight-of-hand of swapping the
cassette...

That's what they expect. With the modified boombox he can stand
on the other end of the stage and have an audience member do the
magic.

 

[Guy Macon]

Rich Grise wrote:

Guy Macon wrote:

John Woodgate wrote:

It is pretty simple, but for one thing - it's very difficult if not
impossible to get technical information on boom-box circuitry unless
it's an up-market product and you are an authorised dealer, and such
information is almost certainly necessary.

It sounds to me as if you could do it simply by accessing the
microphone, speaker, and switches - no knowledge of the internals
needed.

Someone else mentioned having engineers and/or tech examine the box
for spoofs - in that case, you'd have to get one with one main processor,
and rewrite the ROM.

I disagree, unless the engineers/techs are allowed to dissasemble it.
I was thinking of having them examine it to see that it works like
a normal boombox should.

 

[G]

Thanks all for your input........Jim Adney for reading the post closely and
offering some logical thinking to this.
My selective power-down of the rest of the house was by first unplugging
the couple of wallwarts, UPS on the computer, then anything and everything
else which is why it had me in head scratch mode when the new TV showed the
same symptoms. Your comment on the AC (modulating) the pic causing the
slow roll up makes me wonder whether I've got a ground loop (poor bonding
etc) within the house (can't fathom why this would cause the problem except
for any of these sets being transformerless) or something as odd as
crosstalk from another power phase out at the power pole (or just radiation
from same). Anyway, not bad enough to ruin our viewing worse than the
actual programming but good enough for a wonder-why.


Thanks again all


Gord

 

[Bob Parker]

If I remember correctly, there's a small electrolytic cap in the
mains detection section of the speaker protection circuit which goes
open circuit. It's maybe 1uF or 10uF... years since I worked on those.
I don't know why the unit would shut down after a few hours though.
Good luck with it.

Cheers,
Bob


dbacks@attglobal.net wrote:

I have a Yamaha R-900 Receiver that has worked flawlessly up until
about a week ago.

About one out of four times that I switch it "on" the protective
circuit relay does not engage.

Also, if I leave it on for several hours, the receiver will shut down.
Any suggestions?

Thanks,

Mark

 

[Bob Stephens]

On 28 Dec 2004 03:48:13 GMT, Roger Johansson wrote:

It
doesn't mean anything to people who have already made millions working
for NASA,

Umm... I've done work for NASA and I don't recall any millions coming my
way. Should have negotiated better I guess.

Bob

 

[AshTray700]

well at any rate with all of this , its time for everybody on this planet
to wake up and smell the roses, there is no "mother nature" controlling
all of the life sustaining elements on this planet , they will go away,
everybody gets in this whole "god is taking care of us" state of mind and
therefore they ignore the facts. this planet will eventually no longer
suppport life period and if we do not develop technology that allows us to
migrate off it we will go down with it. so lets try and keep it livable as
long as possible to give our scientist the opportunity to develop a method
of deep space travel (if one exists) so that all of this shit we go
through to continue the human race is not in vain

 

[Guy Macon]

Roger Johansson wrote:

When a magician hangs a seemingly empty cage from the ceiling of a
nightclub, covers it in black cloth, and seconds later removes the cloth
and there is a white tiger in the cage.. that is totally boring to me.
Anybody can do that trick, if he can afford to buy the machinery that is
needed.

Go to a Penn and Teller show and try to figure out how they do it..

 

[Asimov]

"Monty Hall" bravely wrote to "All" (27 Dec 04 14:25:15)
--- on the heady topic of "Op-Amp Design - Stage 2 Current to Voltage"

MH> Reply-To: "Monty Hall" <chickenkungpao@hotmail.com>
MH> Xref: aeinews sci.electronics.repair:4845

MH> I'm reading Tom Frederickson's "Intuitive IC Op Amps" - in particular
MH> pg 15 concerning the op-amp schematic, and am not sure how the second
MH> stage of the op amp works. This stage that takes the single ended
MH> current and converts it a voltage before it's off to the output stage.

MH> The current input goes to the base of a transistor whose emitter is
MH> connected directly to ground and the freq compensating capacitor is
MH> placed across the collector and base. How does this configuration work
MH> - especially if the base input current is negative? Current is sourced
MH> from cap?

MH> Horowitz and Hill's 741 schematic has a 300 ohm resistor on the base
MH> input. Is this where the current to voltage conversion takes place and
MH> was omitted by Frederickson? In either case, still not sure where
MH> current comes from when current mirror sinks current in stage 1.

MH> If the sinking current mirror pulls from the cap, I would expect the
MH> mirror, when sourcing current, to load the cap by symmetry. But in a
MH> sourcing configuation, the transistor is now forward biased. If
MH> current is being sunk
MH> @ constant rate, wouldn't the magnitude of the voltage across the cap
MH> ramp wrt time? I expected the output voltage to be proportional to
MH> input differential voltage and not ramp in an open loop config.

MH> Can somebody explain how current is converted to voltage in stage 2 of
MH> an op-amp?

MH> Totally unrelated, but what does it mean when a NPN transistor has two
MH> or more emitters in a schematic?

MH> Thanks,


Monty, current is converted to a voltage by flowing through a
resistor. It is that simple as you may have noticed. However the
compensation cap is a dynamic element which must be dealt with as a
small signal AC network and not as a large signal static charging
element. I think this is why you are confused.

To approach the problem from the small signal viewpoint the input
resistance or impedance of the transistor stage must be measured or
approximated (educated guess). In the common emitter transistor, the
base impedance is equal to about Vt/Ib where Ib is the DC base current
and Vt is a constant (but varies with temp) ranging from about 20mV to
40mV (depending on construction), often a 25mV approximation is used.
The effective capacitance across the base impedance is multiplied by
the transistor voltage gain (Miller Multiplication). As an example for
a voltage gain of 100 a 200pF cap reflects as a 20nF cap across the
base impedance. This results in a lp pole to limit the phase shift to
a predictable value for the frequency compensation. If the cap wasn't
used the phase shifts of all the stray caps would add up to make the
amp unstable at some frequency and with a lot of gain. A bad thing.

About multiple emitters, this is a feature of integrated circuits
where the transistor structure divides the collector current into more
than one emitter. This is often done to get very close matching for
temperature compensation or to get a very precise current division.
Sometimes it is simply for isolation between supplied circuits when
used as a reference emitter follower to bias various stages.

Good luck in your studies!

A*s*i*m*o*v

.... Over a hundred billion electrons were used in crafting this tagline.

 

[Frithiof Andreas Jensen]

"Matt J. McCullar" <mccullar@flash.net> skrev i en meddelelse
news:tn2Ad.6155$_X7.2005@newssvr33.news.prodigy.com...

Dad is looking for make, model number, and perhaps part number for the
thermostat, and I promised I'd look on the Internet for help.

It's often easier to go to a "appliance spareparts store" with the Maker &
Model details - they will know which parts you need, if they are available
and whether the manufacturer has had some problems with that product: My old
Electrolux dishwasher needed three PCB's and some special cable-glands in an
"upgrade kit" to fix a problem with *one* PCB Burning when the dishwasher
overflowed.

 

[AshTray700]

you can get one for $15 at the local walmart that will work in the 88mhz
range, if you want full fm capabilities you have to add like $10 to that,
they do work, but if you are an audiophile you will not be impressed
because the sound quality is not so great but they are cheap and they run
off AAA batteries for days constantly before going dead, what i would
really like to know is where to get diagrams and parts to build a
powerfull fm transmitter, like a few miles powerfull

 

[James Sweet]

"AshTray700" <ashtray700@aol.com> wrote in message
news:083fb9fa44caece95934ffea2b54a07a@localhost.talkaboutelectronicequipment.com...

you can get one for $15 at the local walmart that will work in the 88mhz
range, if you want full fm capabilities you have to add like $10 to that,
they do work, but if you are an audiophile you will not be impressed
because the sound quality is not so great but they are cheap and they run
off AAA batteries for days constantly before going dead, what i would
really like to know is where to get diagrams and parts to build a
powerfull fm transmitter, like a few miles powerfull

Ramsey sells these also, likely cheaper than you could build one, but if you
live in the US, operating one without a license is a good way to get a very
large fine/jail time.

 

[AshTray700]

the voltage regulator is probably out and thats why that resistor is
burned, if you change it, you will just roast another one. look for the
nearest chip attached to a heat sink , flip the pcb and look at the
traceings, are they browned? check the diodes nearby also, voltage
regulator chip (trnasistor type = around $5 or so, ic type up to like $30)
from my experience just about all tv sets with power supply failures like
that (burned components, or no power) are due to a bad vr chip, it
produces a lot of heat and wears out due to it, if you change it make sure
that you attach it back to the heat sink with the heat transfer grease or
patch in place if it has one. you will need to replace the resistor as
well and any other component damaged due to excessive current

 

[AshTray700]

pop up ads (the really annoying ones) are a result of spyware opening up
inbound communication on your pc, you pick up spyware all over the
internet if you are not carefull what you click on, and sometimes it can
get in without you doing anything, if you are going back to dialup, you
need to download ad aware se and run it to clean up all the spyware you
got with the fast connection, you are less likely to get gobs of spyware
with a dialup connection that is only on when you want it to be, if your
computer is fairly new and you have removed spyware you will have no
problems with dial up connection. at any rate ad aware is a great tool,
install it and make friends with it sometimes it gets lonely and needs
company from his pal Norton Antivirus. and always update your windows
software via windowsupdate. then above all dont click on those stupid
windows that pop up and dont get software off the internet (kazaa, screen
savers, games) you may think they are free, but they get their revenue
from advertising to you and are packaged with spyware.

 

[AshTray700]

speaking of fcc rules, what is the limitation of power you can operate
without having to be sneaky about it

 

Hi,
To adjust the tracking on this camcorder probably involves changing the
position of the tracking guides usually #6 and 3 by loosening the
locking screws at the base of each guide and changing the position of
the guides.
HOWEVER if you do this it will be very difficult to return to the
proper adjustments without an alignment tape and the Track shift and
monitor jig J-16:J-6080-843-A which only an Sony tech would have. If
you'r interested in the adjustment procedure I can copy/scan and
send/email it to you. ( I only have the manuals for the V5 and V9 but
I think they're very simular.
Richard