Toshiba TV29C90 problem; Image fades to black...

[Franc Zabkar]

On 31 Mar 2005 00:38:35 -0800, rogersa@radstone.co.uk (Andrew Rogers)
put finger to keyboard and composed:

This TV was dead but I found 5 parallel i ohm resistors o/c (not
burnt) in the SMPS. Replaced and now emits regular faint clicking
sound.
Anyone got a circuit diagram please? - I've searched everywhere.
The SMPS uses a 16 pin TDA8380A and BUW13 NPN power transistor with a
CNG82A optical coupler for the feedback. What is it safe to try?
Don't think the transisot is faulty.

See the application diagram on page 68 of this datasheet:

The GTV1000 Global TV Receiver:
http://www.semiconductors.philips.com/acrobat_download/applicationnotes/AN98051_1.pdf


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[John Woodgate]

I read in sci.electronics.design that Leon Heller
<leon_heller@hotmail.com> wrote (in
<424c6234$0$291$cc9e4d1f@news-text.dial.pipex.com&gt about 'Transistors
Checking Troubleshooting - BJTs, FETs', on Thu, 31 Mar 2005:

The (forward-biased) resistance of the base-collector junction is
usually lower than that for the base-emitter junction. The difference
is quite small, though.

I use a wet finger between base and emitter both to identify the emitter
and get a rough idea of beta from how much collector current results.
Then reverse the (assumed) emitter and collector connections and apply
the same wet finger. Less current means reverse beta applies.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[kip]

Whats the Make ?
Sounds like bad CRT .

kip

"Lanzar" <christian.loo@netikka.fi> wrote in message
news:677fafc5.0503311238.6929d6cc@posting.google.com...

I have a television with a strange problem. When i start the tv it
takes about 10-15 seconds before the picure appears. And also the red
color is missing, so the piture is bluegreen (but no lines). And then
after about a half minute red fields starts flashing across the
screen, and then it turnes off. Any idea what cause this?

 

[jakdedert]

Danny Kewl wrote:

I have a Nokia 3650 cell phone which takes a BL-5C battery. The
battery charges inside the phone. The charging module on the phone
went bad, so a cell phone repair place ordered one and will install
it when they hopefully receive it in a few days. In the meantime, I
have no way to charge the battery to use my phone until I get it
fixed. Can I alligator clip the wires from a DC power adaptor (wall
wart) to the terminals of the battery after cutting off the adaptor
on the end? What voltage/amps would I use (give me a range if
possible) and it looks like there's three terminals on the battery,
but which are positive and which negative? How long to charge? The
battery says 3.7 Vlots Li-ion, made by Nokia. It doesn't say amps but
I think it's rated for 850 milliamp hours?I'm guessing the battery is
about 1.5 by .75 inches, and very thin. I have some pics of the
battery here, they're a bit blurry as the camera phone isn't good at
close shots:

I wouldn't mess around trying to charge the thing out of the phone unless
you know what you're doing, and use the proper supply.

OTOH, there are external chargers available for most Nokia phones. Check
your local home electronics supplier (or perhaps Wal Mart...I've bought them
there....).

jak

http://img.photobucket.com/albums/v725/DannyWho/Image02.jpg

http://img.photobucket.com/albums/v725/DannyWho/Image03.jpg

http://img.photobucket.com/albums/v725/DannyWho/Image04.jpg


Thanks very much,

Dan

 

[NSM]

"James Sweet" <jamessweet@hotmail.com> wrote in message
news:_lN2e.18484$Go4.12142@trnddc05...

Adding a headphone jack creates a shock hazard, but you already have one
so
you'll have no problems. To connect the speakers you'll need an amplifier
of
some sort, doesn't have to be anything fancy. You may need a couple
resistors to match the impedance but that may not be nessesary.

Powered computer speakers are an easy way to go.


--
N

 

[NSM]

<genenamg@yahoo.com> wrote in message
news:1112291657.595936.40770@z14g2000cwz.googlegroups.com...

How do I check if a transistor is working using a multimeter - both
BJTs and FETs? How will I know if it's shorted etc? Also, for a BJT
how will I know the emitter, base and collector by using a multimeter?

You need a 100K resistor. Find out the polarity of your analog multimeter on
ohms. Connect it correctly from collector to emitter. Now add the resistor
from collector to base. Note the two readings.


--
N

 

[Charles Schuler]

Could be an over-current protection circuit kicking in.

 

[Charles Schuler]

I use a wet finger between base and emitter both to identify the emitter
and get a rough idea of beta from how much collector current results. Then
reverse the (assumed) emitter and collector connections and apply the same
wet finger. Less current means reverse beta applies.

A wet finger across the base-collector terminals will turn a good device on
and the ohmmeter reading will drop accordingly (assuming the ohmmeter is
connected across C-E with the correct polarity for NPN or PNP).

 

[Jana]

You should always mention the make and model number of your TV set when
posting.

Generally speaking, it sounds like the CRT is most likely defective. CRT
replacement in a typical TV set, or computer monitor, generally costs more
than a new unit.

--

JANA
_____


"Lanzar" <christian.loo@netikka.fi> wrote in message
news:677fafc5.0503311238.6929d6cc@posting.google.com...
I have a television with a strange problem. When i start the tv it
takes about 10-15 seconds before the picure appears. And also the red
color is missing, so the piture is bluegreen (but no lines). And then
after about a half minute red fields starts flashing across the
screen, and then it turnes off. Any idea what cause this?

 

[Jana]

Why not get the proper external charger for your phone battery?

DO NOT mess around with the battery from your phone. It can easily be
damaged, by not charging it in the proper current window, with the proper
control over the charge rate. Over charging this type of battery, can also
lead to it to explode. Besides, if you ruin the battery, the cost of it is
fairly expensive!

--

JANA
_____


"Danny Kewl" <bwana1SPAMMENOTREMOVE@lycos.com> wrote in message
news:ep6dnU-Em4YCx9HfRVn-iw@adelphia.com...
I have a Nokia 3650 cell phone which takes a BL-5C battery. The battery
charges inside the phone. The charging module on the phone went bad, so a
cell phone repair place ordered one and will install it when they hopefully
receive it in a few days. In the meantime, I have no way to charge the
battery to use my phone until I get it fixed. Can I alligator clip the wires
from a DC power adaptor (wall wart) to the terminals of the battery after
cutting off the adaptor on the end? What voltage/amps would I use (give me a
range if possible) and it looks like there's three terminals on the battery,
but which are positive and which negative? How long to charge? The battery
says 3.7 Vlots Li-ion, made by Nokia. It doesn't say amps but I think it's
rated for 850 milliamp hours?I'm guessing the battery is about 1.5 by .75
inches, and very thin. I have some pics of the battery here, they're a bit
blurry as the camera phone isn't good at close shots:

http://img.photobucket.com/albums/v725/DannyWho/Image02.jpg

http://img.photobucket.com/albums/v725/DannyWho/Image03.jpg

http://img.photobucket.com/albums/v725/DannyWho/Image04.jpg


Thanks very much,

Dan

 

[testortool]

Probably a bad CRT. I have an almost mint early 70s Sony Trinitron 13" TV
that has a "flaky" red gun that cuts in and out kind of like what you're
seeing. Usually when CRT color guns go bad, the red one goes first.

"Lanzar" <christian.loo@netikka.fi> wrote in message
news:677fafc5.0503311238.6929d6cc@posting.google.com...

> Any idea what cause this?

 

[testortool]

If the scratch is directly on the lens screen it's going to be costly with
no way of rubbing it out completely. There are companies on the net that
specialize in new custom made lens screens for most rear projection TVs,
even old models, but in most cases it's going to run several hundred
dollars. You can buy fairly nice rear projection TVs now for around $1000.

"Jeff" <jaribus_jarobi@hotmail.com> wrote in message
news:1111946093.039913.168070@z14g2000cwz.googlegroups.com...

> Can anybody help me out with any other suggestions?

 

[Fritz Schlunder]

<genenamg@yahoo.com> wrote in message
news:1112291657.595936.40770@z14g2000cwz.googlegroups.com...

How do I check if a transistor is working using a multimeter - both
BJTs and FETs? How will I know if it's shorted etc? Also, for a BJT
how will I know the emitter, base and collector by using a multimeter?

You can generally get a good idea of a MOSFET's condition by making a simple
resistance measurement between the gate and source leads. The MOSFET's gate
oxide is quite thin and fragile, so if the MOSFET fails one of the
consequences will be that it will normally damage the gate oxide (even if
the gate itself wasn't abused by excessive voltage). A failed MOSFET will
normally measure <1k ohms between gate and source. These failed MOSFETs
will also normally exhibit low resistance from drain to source as well. A
good MOSFET's gate to source resistance will measure somewhere in the
megohms to infinity range.

There are exceptions to this however. Sometimes the failure (especially in
the case of power MOSFETs used in such a way that if they fail large
currents flow) is so catastrophic that internal fusing can occur. Sometimes
enough transient power can be dissipated in the device to physically blow
the plastic package apart, physically separating one of the leads from the
die. In these types of failures the above mentioned resistance test may
read infinity even though the device is definitely broken. In my experience
these types of failures are relatively uncommon compared to more mundane
failures which simply result in low resistance shorts between the three
pins. When they do fail like this it is often obvious since the plastic
package has literally blown apart or has otherwise suffered evident trauma.

In one case I found a 2N7000 MOSFET that failed by means of a parametric
shift. The drain to source became very leaky (comparable to a 100k ohm
resistor) even though the gate was fully intact. The device still worked
fine, besides the extra leakage. The leakage current could be reduced by
driving the gate with negative gate-source potential, but still not
completely turned off. I have no idea what might have happened to this
device to cause this failure. Nevertheless I think this is a very rare
failure mode which you shouldn't normally need to worry about.

 

[Ken Weitzel]

gcotterl@co.riverside.ca.us wrote:

A couple of months ago, I installed a new Terk TV38 antenna, an antenna
rotator and new coax cables. But the reception is very poor for most
of the channels, even when I rotate the antenna thru the entire 360
degrees.

All of the connections from the antenna to the TV are good.
I've even run a new coax cable directly from the antenna to the TV.
But the reception is still poor.

(I have two TV sets and both get bad reception so the TVs are NOT the
problem).

My house is in Riverside, CA (about 60 miles east of Los Angeles).
Almost all of the stations broadcast from transmitters on Mt. Wilson
(49 miles northwest of my house).

On a scale of "1" (extremely snowy picture and very garbled sound)
to "10" (crystal-clear picture and sound), here are the
"reception"-ratings for the channels I watch:

Channel Rating
2 3
4 4
5 3
7 7
9 8
11 4
13 6
24 2
28 7
56 8
58 8

Any suggestions?

Hi...

Wrong cable impedance? (59/75/300, etc)

Don't know the antenna, but no balun at the head end?

Ken

 

[Ken Weitzel]

gcotterl@co.riverside.ca.us wrote:

What is a "balun"?
What is the "head end"?

Hi...

Balun is silly talk for balanced/unbalanced... the little
transformer that connects the 300 ohm antenna to the (hopefully)
75 ohm coax.

The head end is silly talk for the antenna proper...

Ken

 

[Asimov]

"John Woodgate" bravely wrote to "All" (31 Mar 05 22:29:51)
--- on the heady topic of "Re: Transistors Checking Troubleshooting - BJTs,
FETs"

JW> From: John Woodgate <jmw@jmwa.demon.contraspam.yuk>
JW> Xref: aeinews sci.electronics.repair:44620

JW> I use a wet finger between base and emitter both to identify the
JW> emitter and get a rough idea of beta from how much collector current
JW> results. Then reverse the (assumed) emitter and collector connections
JW> and apply the same wet finger. Less current means reverse beta
JW> applies. --

I use a variation of this tip to get a relative indication of
transistor action. Simply connect an analog ohmmeter leads, on highest
ohms range, to polarize the collector and emitter while leaving the
base floating. Then, without touching the other pins, lightly touch
the base terminal and watch the indication on the meter scale. The
higher the gain the higher the deflection. The idea is that the
base-emitter junction rectifies the ambient RF field picked up by your
body and results in a collector current through the ohmmeter.
Clearly not as intuitive with a DMM.

A*s*i*m*o*v

.... When I was your age, we carved transistors out of wood.

 

[Franc Zabkar]

On 31 Mar 2005 03:12:15 -0800, shaun.davy@iinet.net.au (Shaun Davy)
put finger to keyboard and composed:

Hi,

Im working on a NEC TV that has no vertical deflection (white
horizontal line). There is no O/P on Pin 1 which is the vertical drive
to the deflection amp (TDA3654). I have replaced the TDA2579 chip and
still no drive on pin 1. Checked pin 3 with external cap and there is
a proper sawtooth waveform there. Pin 2 has about 1.8V on it taking it
just short of blanking the sandcastle O/P. Pin 4 (vert def current)
appears dead which i assume would be due to no drive to vert amp and
then no O/P. I have lifted off pin 1 of the TDA2579 and still nothing.

Any idea's to what could be causing this? there is horizontal
defelection so chip has to be powered up. Could there being no
feedback cause it to have no O/P, therefore the vertical amp possably
being dead?

Cheers,
Shaun

I'd check the supply to the vertical amp. There could be an OC fusible
resistor.

As for your horizontal white line, did you need to adjust the screen
voltage in order to see it? I ask this because the TDA2579 datasheet
has this to say:

"The IC also contains a vertical guard circuit. This circuit monitors
the vertical feedback signal on pin 2. When the level on pin 2 is
below 0.35 V or higher than 1.85 V the guard circuit inserts a
continuous level of 2.5 V in the sandcastle output signal of pin 17.
This results in the blanking of the picture displayed, thus preventing
a burnt-in horizontal line. The guard levels specified refer to the
zener diode reference voltage source level."


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Franc Zabkar]

On Thu, 31 Mar 2005 13:06:38 -0500, Keith Williams <krw@att.bizzzz>
put finger to keyboard and composed:

In article <1112291657.595936.40770@z14g2000cwz.googlegroups.com>,
genenamg@yahoo.com says...
How do I check if a transistor is working using a multimeter - both
BJTs and FETs? How will I know if it's shorted etc? Also, for a BJT
how will I know the emitter, base and collector by using a multimeter?

BJTs are easy: A BJT will look like two diodes (Base-Emitter and Base -
collector). Find the common lead. That's your base. If the
transistor conducts ('+' to '-') from the base to the other two, it's
an NPN. If it conducts the other way it's a PNP. If it conducts both
ways or neither, pitch it.

Before discarding them, be aware that some transistors have a diode
between collector and emitter, while others have resistors between the
base and emitter. Then there are digital transistors ...


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[John Woodgate]

I read in sci.electronics.design that Charles Schuler
<charleschuler@comcast.net> wrote (in
<P_ydnW7Ly91vGdHfRVn-vA@comcast.com&gt about 'Transistors Checking
Troubleshooting - BJTs, FETs', on Thu, 31 Mar 2005:

I use a wet finger between base and emitter both to identify the emitter
and get a rough idea of beta from how much collector current results. Then
reverse the (assumed) emitter and collector connections and apply the same
wet finger. Less current means reverse beta applies.

A wet finger across the base-collector terminals will turn a good device on
and the ohmmeter reading will drop accordingly (assuming the ohmmeter is
connected across C-E with the correct polarity for NPN or PNP).


Sorry, my article is screwy. THIS is what I should have written:

I use a wet finger between base and COLLECTOR both to identify the
collector and get a rough idea of beta from how much collector current
results. Then reverse the meter connections and apply the same wet
finger between base and what you believe is the emitter. Less current
means reverse beta applies.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[burbeck]

On 31 Mar 2005 09:54:17 -0800, genenamg@yahoo.com wrote:

How do I check if a transistor is working using a multimeter - both
BJTs and FETs? How will I know if it's shorted etc? Also, for a BJT
how will I know the emitter, base and collector by using a multimeter?


Thanks,
GN

try this http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

regards
bob