Toshiba TV29C90 problem; Image fades to black...

[Asimov]

"amcwill417" bravely wrote to "All" (05 Nov 05 22:59:36)
--- on the heady topic of "Re: Problem for 15 year old 32" TV"

am> From: "amcwill417" <amcwill417@email.msn.com>
am> Xref: core-easynews sci.electronics.repair:347676

am> A HAPPY EVENT!
am> This Saturday evening I opened up the TV and removed one of the
am> circuit boards for inspection and resoldered some suspicious looking
am> solder joints. Then I replaced it and turned on the set and nothing
am> changed - set still did not work. Then I turned on the TV and pushed
am> down on the HV transformer with a long stick so as to distort the
am> circuit board it is on and WHALA that did the trick. The set now works
am> fine!!! I guess I will have to resolder components on this board
am> sometime soon since I suppose there must be a loose solder joint
am> somewhere. I do not understand why this Sony TV has had so many
am> defective solder joints. It is a wonder that it has worked at all
am> over these many years.


Alex,

Heat around power devices will cause thermal expansion and then
contraction when cooled. Eventually the solder becomes metal fatigued
and brittle. This increases resistivity of the solder and the joint
can even burn up in extreme cases.

Case in point, when replacing power transistors in audio amplifiers I
always used to leave a little semi-circular bend to the leads so that
as the devices heated up the bend would take up the slack and wouldn't
pull when cooled again.

A*s*i*m*o*v

.... Wasted power is current squared times the resistance.

 

[frontline@nospam]

Thanks Ron, Soldering and the design layout in this model looked great
very few signs of heat.
Jeff

 

[Colin McCormick]

Hello

I've got a F-Z92L tuner, which may be compatible
with your system (connected via a short ribbon
cable and connector). Yours for the price of UK
postage or collect from Devon. Being quite
light I would expect it to cost Ł7.20 to post.

Contact me directly on colin99@bigfoot.com if
this is of use to you.

Regards,

Colin


geert@user1.be wrote:

Hi everybody

I have a pretty old Pioneer Tuner F-Z93L part of an entire stereo
device S111. The problem with the tuner is that it keeps searching on
the entire FM-band in order to find a station. It never stops.
I think it has something to do with the treshold level to distinguish
noise / signal.

In it, I descovered a PCB with number ANPI356-B. There's another PCB
near the front, carrying the LCD and some other stuff.

Has anyone advice upon this, similar problems in another tuner, a
schematic diagram would be perfect

Thanks for help

Eng. GDB

 

[amcwill417]

"Asimov" <Asimov@-removethis-bbs.juxtaposition.dynip.com> wrote in message
news:MSGID_1=3a167=2f133.0_436e0ebf@fidonet.org...

"amcwill417" bravely wrote to "All" (05 Nov 05 22:59:36)
--- on the heady topic of "Re: Problem for 15 year old 32" TV"

am> From: "amcwill417" <amcwill417@email.msn.com
am> Xref: core-easynews sci.electronics.repair:347676

am> A HAPPY EVENT!
am> This Saturday evening I opened up the TV and removed one of the
am> circuit boards for inspection and resoldered some suspicious looking
am> solder joints. Then I replaced it and turned on the set and nothing
am> changed - set still did not work. Then I turned on the TV and pushed
am> down on the HV transformer with a long stick so as to distort the
am> circuit board it is on and WHALA that did the trick. The set now
works
am> fine!!! I guess I will have to resolder components on this board
am> sometime soon since I suppose there must be a loose solder joint
am> somewhere. I do not understand why this Sony TV has had so many
am> defective solder joints. It is a wonder that it has worked at all
am> over these many years.


Alex,

Heat around power devices will cause thermal expansion and then
contraction when cooled. Eventually the solder becomes metal fatigued
and brittle. This increases resistivity of the solder and the joint
can even burn up in extreme cases.

Case in point, when replacing power transistors in audio amplifiers I
always used to leave a little semi-circular bend to the leads so that
as the devices heated up the bend would take up the slack and wouldn't
pull when cooled again.

A*s*i*m*o*v

... Wasted power is current squared times the resistance.

A good practice. Based on my several experiences with this television may I

put forward a first rule for repair: First bang (somewhat gently)
everything you have access to - like kicking the tires of an older car. If
the trouble goes away even temporarily then suspect a loose connection
somewhere. For TVs or other devices with high voltages use a long insulated
rod, say a 3 foot long dry plastic rod, for safety.

Alex

 

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.

 

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.

 

[Franc Zabkar]

On Sun, 6 Nov 2005 22:55:11 -0800, "MJ" <mj@address.invalid> put
finger to keyboard and composed:

My Panasonic cordless phone KX-TG2553B used to work fine. Now people I call complain
(and I have verified) that the handset mic volume is extremely low. Changing the phone
volume has no effect. Don't know if the handset was dropped -certainly possible though.
Do these mics ever go bad? I took it apart and found nothing obvious. It cost $125 bucks
in '02 and has been a great phone. TIA

Have you recently switched to DSL? Panasonic phones have a known issue
with some filters.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

 

[Brad Houser]

On 6 Nov 2005 17:55:04 -0800, do_not_spam_me@my-deja.com wrote:

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.

OK, so we eliminated the obvious. The typical PC crystal costs $.25 and is
accurate to 20ppm, or 1.7 sec/day, at room temp. It gets worse at other
temps. You can buy a pci clock card with a tempurature compensated crystal
that is accurate to plus or minus 2ppm for $60, and make it your time
server for you network, or if stand alone systems, in each one if it is
that important. Here is one: http://www.beaglesoft.com/clcaspecs.htm

BH

 

[Blinky the Shark]

Brad Houser wrote:

OK, so we eliminated the obvious. The typical PC crystal costs
$.25 and is accurate to 20ppm, or 1.7 sec/day, at room temp. It
gets worse at other temps.

Is there a simple relationship like slower-cooler and faster-hotter
(or the reverse) involved here, or is the relationship not that
simple?


--
Blinky
Killing all Google Groups posts.
http://blinkynet.net/comp/uip5.html

 

[w_tom]

The crystal time function also gets worse when voltage to
that oscillator varies. And that voltage variation is part of
the CMOS date time clock design. Oscillator accuracy, which
addressed the OP's original question, was answered at the very
beginning of this thread. Variation of oscillator crystal is
why watches have a trimmer capacitor. But this too was
answered up top, at the beginning, maybe about 100 replies
ago. Worse still, something like 3 out of 4 responses still
post about external time sources - WWV, internet time,
Operating System response to a interrupts from a completely
different clock, etc. All those were obviously and totally
irrelevant to the question originally asked by do_not_spam_me.

His question was answered early on in the very first
responses. Following posts should deal with these - two
factors of oscillator variation - no trimmer capacitor and
voltage variations to that oscillator. So many reponses that
never once even considered these factors that cause CMOS RTC
timing variations.

BTW, John Popelish also provides good information on how
crystal cuts and other factors contribute to these
variations. Another post that answers the OP's original
question and a comment about many posts that don't.

Brad Houser wrote:

OK, so we eliminated the obvious. The typical PC crystal costs $.25
and is accurate to 20ppm, or 1.7 sec/day, at room temp. It gets worse
at other temps. You can buy a pci clock card with a tempurature
compensated crystal that is accurate to plus or minus 2ppm for $60,
and make it your time server for you network, or if stand alone
systems, in each one if it is that important. Here is one:
http://www.beaglesoft.com/clcaspecs.htm

 

[Skype_man]

2.4 ghz cordless phones really perform badly near any microwave
oven, when cooking. Having said that, may just be a bad mic, or
some debri in the hole for the mic. Sky.

 

[Michael Kennedy]

I have found this to be a common problem with panasonic phones. I don't know
the cause but mine has the same problem as well as my friends's panasonic
phone.


"MJ" <mj@address.invalid> wrote in message
news:2_GdnZZQJe7MZ_PeRVn-hA@centurytel.net...

My Panasonic cordless phone KX-TG2553B used to work fine. Now people I
call complain (and I have verified) that the handset mic volume is
extremely low. Changing the phone volume has no effect. Don't know if the
handset was dropped -certainly possible though. Do these mics ever go bad?
I took it apart and found nothing obvious. It cost $125 bucks in '02 and
has been a great phone. TIA

 

[MJ]

I did some internet searching but couldn't find much on Panasonic low volume problems.
I'm going to try plugging in a headset into the handset and see if that bypasses the
problem. A friend has this identical phone which I tried in my base unit and it works
fine - so I know the trouble is with my handset itself. I'd swap out the mic if I knew
where to find a replacement.


"Michael Kennedy" <Mikek400@remthis.comcast.net> wrote in message
news:bZudndmQGptlhe3eRVn-gA@comcast.com...

I have found this to be a common problem with panasonic phones. I don't know the cause
but mine has the same problem as well as my friends's panasonic phone.


"MJ" <mj@address.invalid> wrote in message
news:2_GdnZZQJe7MZ_PeRVn-hA@centurytel.net...
My Panasonic cordless phone KX-TG2553B used to work fine. Now people I call complain
(and I have verified) that the handset mic volume is extremely low. Changing the
phone volume has no effect. Don't know if the handset was dropped -certainly possible
though. Do these mics ever go bad? I took it apart and found nothing obvious. It cost
$125 bucks in '02 and has been a great phone. TIA

 

John Fields wrote:

On Fri, 04 Nov 2005 01:59:05 -0500, jh <no@thanks.com> wrote:

Hi,

I was hoping somebody here might be able to help me with a question.
First, some background. A couple of months ago I was trying to record
the sounds of the insides of my computer for an experimental sound
project. I first tried it with a cheap, crappy lapel mic that came with
a pocket voice recorder. It worked just fine.

Then I borrowed a fairly nice, high quality microphone and tried it
again. Sure enough, this microphone picked up a lot more sounds... in
fact, it recorded all sorts of beeps, buzzes, and hums that weren't even
there, apparently some sort of electromagnetic interference. I was
amused to find that this high-quality microphone was much more prone to
picking up this interference than the cheap one I tried earlier.

The thing is, the interference sounds were much more interesting than
the real sounds. Holding the microphone near the graphics card, it
recorded different noises depending on what was being displayed on
screen. The fans sounded like something out of a science fiction movie.
My personal favorite sound came from the power cord while the computer
was asleep: it made a bizarre sequence of changing pitches that repeated
every couple of seconds.

The only problem is, all of these great interference-caused phantom
sounds were almost drowned out by the actual normal sound produced by
the fans, hard drive, etc. in the computer. Needless to say, the
microphone was quite adept at recording these sounds.

So my question is this: is it possible to build a device, or modify a
microphone, so that it picks up ONLY the electromagnetic interference,
but no actual sound?

---
If your mic was picking up EMI and also acoustic sound you could
probably get rid of a large amount of the acoustic sound by
shielding the mic's diaphagm. That is, cover the places where the
sound enters the microphone in order to keep sound out of there.
Maybe cotton balls and Scotch tape?


The other thing you might want to try would be to wind a coil and
substitute it for the mic. I'd start with a couple of hundred turns
of 24 gauge telephone wire wound on an air core just to see what
would happen, and then go on from there.

A telephone pickup is just the thing he is looking for. There are
different kinds of
interference. The electrical has both static and magnetic, which often
sound very
different. I say this because I use a device to look for interference
very
often. I can switch in the coil or or small antenna, to get a sample of
both.
The magnetic will penetrade metal where the static will not. I am still
working on completing my little amplified snooper. I also need to
switch in a photodiode to detect and listen to light noise. I also need
a vibration sensor to detect "vibration".
A low frequency, less than 10 HZ, audio sensor would be good to sense
ventillation noise.
To detect a static magenetic field, I need to rotate my coil, or get a
Hall Effect sensor.

greg

 

[Skype_man]

You MAY find a mic that will work, & fit from a
ghetto blaster, or tape recorder. Sky.




"MJ" <mj@address.invalid> wrote in message
news:2_GdnZZQJe7MZ_PeRVn-hA@centurytel.net...

My Panasonic cordless phone KX-TG2553B used to work fine. Now people I
call complain (and I have verified) that the handset mic volume is
extremely low. Changing the phone volume has no effect. Don't know if the
handset was dropped -certainly possible though. Do these mics ever go bad?
I took it apart and found nothing obvious. It cost $125 bucks in '02 and
has been a great phone. TIA

 

[frontline@nospam]

New part number 483512257004 820pf 2kv is about 4 times larger.
Set is working fine so far.
Jeff

 

[Michael Kennedy]

You could always try radio shack.
"Skype_man" <skype_man@lycos.co.uk> wrote in message
news5idnTnJ0Ml5xezeRVn-tw@rogers.com...

You MAY find a mic that will work, & fit from a
ghetto blaster, or tape recorder. Sky.




"MJ" <mj@address.invalid> wrote in message
news:2_GdnZZQJe7MZ_PeRVn-hA@centurytel.net...
My Panasonic cordless phone KX-TG2553B used to work fine. Now people I
call complain (and I have verified) that the handset mic volume is
extremely low. Changing the phone volume has no effect. Don't know if the
handset was dropped -certainly possible though. Do these mics ever go
bad? I took it apart and found nothing obvious. It cost $125 bucks in '02
and has been a great phone. TIA

 

[tempus fugit]

Thanks JK.

I got a chance to take a closer look at this thing and the neutral wire is
connected to ground, but there appears to be about 200 ohms of resistance
between the ground on the filter cap and the chassis. I didn't see anywhere
were the live wire was connected to the chassis through a cap. Forgetting
about the hum for a second (I'd like to make this whole thing a little safer
1st) would a quick fix for the 120v I've seen on the chassis be to simply
install a polarized plug on the power cord? This way I could ensure that it
was never plugged in backwards thus connecting the chassis to the live 120v
line.

Also, I mentioned a small blue thing that looks like a bunch of thin squares
stacked on top of one another, that someone suggested was a selenium
rectifier. I hear they emit a poison gas when they burn. Would it emit any
dangerous gases during normal operation? Should I make replacing this part a
priority? I should also mention that there is 1 tab on this piece that has
some solder on it but no wires or anything connected to it. Could this be
the source of my hum problems?

Thanks again

"Porky" <juan_morre@hotmail.com> wrote in message
news:1131110191.163461.104640@f14g2000cwb.googlegroups.com...

tempus fugit
Still alive and kicking John, lol.

The "death cap" I assume is the one that is connected
from the live to the chassis? I'm not sure that there even is one in this
unit,

Yes, there is often a .05 or so cap from live to chassis on
transformerless tube gear. It's main purpose is to turn the chassis
into a sheild to keep radio interference.from being detected by the
device. It's secondary function is to shock the @@#$ out of you when it
shorts, (although they are rated at 600v and don't carry much current,
so failures are usually due to moisture and disuse).
If you have small kids, keep them away from the thing. After it is
fixed, install an isolation transformer for $30. Yuo can even build
your own by connecting 2 12V trannys back-to-back. This isolates the
voltages in the chassis from those in your house = no more shocks.
Cheers.

JK

 

[sofie]

hum regardless of volume usually means bad or dried up electrolytic filter
cap(s) and/or maybe a bad rectifier..... and no, during normal proper
operation the selenium rectifiers do not emit poison gas. I would just
simply bridge the filter cap with a replacement of the same or approximate
value and the same or higher voltage to see if the hum goes away.... which
it probably will given the symptoms you reported.
- - - - - - - - - -


"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:19d54$43735e88$d1d89eef$18245@PRIMUS.CA...

Thanks JK.

I got a chance to take a closer look at this thing and the neutral wire is
connected to ground, but there appears to be about 200 ohms of resistance
between the ground on the filter cap and the chassis. I didn't see
anywhere
were the live wire was connected to the chassis through a cap. Forgetting
about the hum for a second (I'd like to make this whole thing a little
safer
1st) would a quick fix for the 120v I've seen on the chassis be to simply
install a polarized plug on the power cord? This way I could ensure that
it
was never plugged in backwards thus connecting the chassis to the live
120v
line.

Also, I mentioned a small blue thing that looks like a bunch of thin
squares
stacked on top of one another, that someone suggested was a selenium
rectifier. I hear they emit a poison gas when they burn. Would it emit any
dangerous gases during normal operation? Should I make replacing this part
a
priority? I should also mention that there is 1 tab on this piece that has
some solder on it but no wires or anything connected to it. Could this be
the source of my hum problems?

Thanks again

"Porky" <juan_morre@hotmail.com> wrote in message
news:1131110191.163461.104640@f14g2000cwb.googlegroups.com...
tempus fugit
Still alive and kicking John, lol.

The "death cap" I assume is the one that is connected
from the live to the chassis? I'm not sure that there even is one in
this
unit,

Yes, there is often a .05 or so cap from live to chassis on
transformerless tube gear. It's main purpose is to turn the chassis
into a sheild to keep radio interference.from being detected by the
device. It's secondary function is to shock the @@#$ out of you when it
shorts, (although they are rated at 600v and don't carry much current,
so failures are usually due to moisture and disuse).
If you have small kids, keep them away from the thing. After it is
fixed, install an isolation transformer for $30. Yuo can even build
your own by connecting 2 12V trannys back-to-back. This isolates the
voltages in the chassis from those in your house = no more shocks.
Cheers.

JK

 

[tempus fugit]

Thanks for your reply Sofie.

I agree with your diagnosis - this reeks of a bad filter cap. The problem is
that the filter cap is an old cardboard multisection with no marks of any
kind on it. There are 4 tabs on the bottom, with the twistlocks acting as
grounds (I think). Of those tabs, 1 shows a 300 or so ohm resistance to one
of the twistlocks. Assuiming that that tab is a cap +, and not a ground,
that cap definitely needs replacing. What I'd like to do is just replace the
lot, but I have no way of knowing what the values of each of the 4 tabs are
supposed to be. Would just replacing them all with, say, 22uF caps be OK?

I'd like to replace the rectifier as well, but I need to figure how to set
up a bridge or diodes properly in the place of the old one. I've never seen
one of these before, but it has 2 tabs on it - + and (-). The (-) tab
acually has nothing connected to it. You can see that it once did, but
doesn't anymore. So..... I'll have to try to figure out where it should have
been connected at one time. Oddly, there is about 150V DC across the filter
caps.

Thanks again



"sofie" <sofie@olypen.com> wrote in message
news:11n7e0bns1tl628@corp.supernews.com...

hum regardless of volume usually means bad or dried up electrolytic filter
cap(s) and/or maybe a bad rectifier..... and no, during normal proper
operation the selenium rectifiers do not emit poison gas. I would just
simply bridge the filter cap with a replacement of the same or approximate
value and the same or higher voltage to see if the hum goes away.... which
it probably will given the symptoms you reported.
- - - - - - - - - -


"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:19d54$43735e88$d1d89eef$18245@PRIMUS.CA...
Thanks JK.

I got a chance to take a closer look at this thing and the neutral wire
is
connected to ground, but there appears to be about 200 ohms of
resistance
between the ground on the filter cap and the chassis. I didn't see
anywhere
were the live wire was connected to the chassis through a cap.
Forgetting
about the hum for a second (I'd like to make this whole thing a little
safer
1st) would a quick fix for the 120v I've seen on the chassis be to
simply
install a polarized plug on the power cord? This way I could ensure that
it
was never plugged in backwards thus connecting the chassis to the live
120v
line.

Also, I mentioned a small blue thing that looks like a bunch of thin
squares
stacked on top of one another, that someone suggested was a selenium
rectifier. I hear they emit a poison gas when they burn. Would it emit
any
dangerous gases during normal operation? Should I make replacing this
part
a
priority? I should also mention that there is 1 tab on this piece that
has
some solder on it but no wires or anything connected to it. Could this
be
the source of my hum problems?

Thanks again

"Porky" <juan_morre@hotmail.com> wrote in message
news:1131110191.163461.104640@f14g2000cwb.googlegroups.com...
tempus fugit
Still alive and kicking John, lol.

The "death cap" I assume is the one that is connected
from the live to the chassis? I'm not sure that there even is one in
this
unit,

Yes, there is often a .05 or so cap from live to chassis on
transformerless tube gear. It's main purpose is to turn the chassis
into a sheild to keep radio interference.from being detected by the
device. It's secondary function is to shock the @@#$ out of you when
it
shorts, (although they are rated at 600v and don't carry much current,
so failures are usually due to moisture and disuse).
If you have small kids, keep them away from the thing. After it is
fixed, install an isolation transformer for $30. Yuo can even build
your own by connecting 2 12V trannys back-to-back. This isolates the
voltages in the chassis from those in your house = no more shocks.
Cheers.

JK