Toshiba RPTV 50H72 - blue screen only

[bharat]

Now I am happy!!! And I agree I have a lot to learn about TV repair.
But with the help from the 'net, I should be able to get this one
working. Hopefully, I won't need to repair another one for a while.

Thanks to everyone who posted help.

I replaced the bad signal board with one from the functioning set.
The TV worked fine. Based on the hints from David and Ken, I think
the TV is going into Blue screen mute mode (the picture looks fine
whenever I could see it). I will check it based on responses from Ken
and David and see if I can get it working this weekend.

Sorry I lost my mind there earlier. When David posted that note saying
I do not have any business doing repairs on electronic systems, it got
my professional "ego" hurt (I guess) (specially because he did not
provide any help in that posting. In retrospect, he WAS proving help
by making sure I do not electrocute myself - without knowing my
background. But at the time, it didn't sound nice). I also
understand from Ken's posting why my statements would not make much
sense. I should have just stayed away from making any comments and
just asked for help. It would have saved a lot of bandwidth! Live
and learn!

Another reason for my temper-tantrum (I guess) was my old habits. I
used newsgroups extensively when I was a grad student. Then, we did
not post anything that was not useful (internet was not
available...only a few people had access to newsgroups. Bandwidth was
low). I always believed the postings were not for money or fame, but
for the satisfaction of helping others (same is true today. If any of
you who helped are waiting for a check from me, you will be waiting a
long time). When I saw David's post, it just irked me that he was
not telling me anything useful (I repeatedly stated in my postings
that if you can't help, stay away...I guess old habits die hard!).

Anyway, I like this newsgroup. I will start reading it on a regular
basis and see if I can provide help. I may not be a good
trouble-shooter, but I am a good designer. If you need help in the
design area, do drop a line.

bharat

 

[David]

You old hat knowledge forgets that modern tv sets have something called blue
screen mute when there is no signal. The fact that there are no retrace
lines on the blue and a normal picture for a second whenever changing
sources 99% rules out a problem with the cathode drive on the blue tube.
There is a possibility that a problem with the AKB circuit could be
overdriving the blue, but an image would still be visible, but very blue.

You are correct in leave the yoke out of it.

The sync however does so much more on a modern tv than causing the picture
to roll or tear horizontally if those are a problem. Without horizontal or
vertical sync pulses to the system control, the tv will shut down to protect
the picture tubes. Without the sync pulses to the jungle ic, odds are no on
screen display will be visible. The signal sync coming off the luminance is
required for the micro to detect the closed captioning information and if
missing will likely result in a blue screen mute.

bharat: another tip here. If you turn on closed captioning in the user menu
since the menu was working, and you select a tv channel that you know is
sending closed captioning (use another tv with it turned on to be sure), do
you get the closed captioning on screen or just a blank box? If closed
captioning is not working, the micro definitely is not seeing the sync
pulses off the incoming signal.

David

"Ken Weitzel" <kweitzel@shaw.ca> wrote in message
news:8PXlc.372803$Ig.110898@pd7tw2no...

bharat wrote:
I haven't had this many arguments over a posting for a long time!!

I own another 52H72 and have troubleshot the power board without any
problem (it did take me a whole weekend to do it). That set kept
turning on and off. I was hoping to avoid a repeat of my "lost"
weekend. I wanted someone to point out the area I should be checking.
I am not that familiar with the signal board and I believe people on
the net have more experience than I will ever have repairing a TV.
Hence the post. I did not want to post a lengthy note on what tests I
did (I checked all power supply lines, H-sync, and yoke drivers. I
have multimeters and a simple oscilloscope). I went through the
schematic. Went through this newsgroup. A previous post mentioned
video amps. There were amplifiers driving the yokes. I assumed that
is what the previous message was talking about when it said video
amps.

If I was wrong, please point it out and point me in the correct
direction. Pointing out my inexperience in repairing a TV is
acceptable, but not providing help and flaming me is not OK. There
are hundreds of postings each day here. If you can't provide help,
don't say anything. Everyone who reads this newsgroup knows (a) a lot
of novices are attempting TV repair who should not, (b) TV repair is
dangerous business, (c) most of these novices will harm themselves
(darwinian principle at work) and learn along the way not to do it
again (as David's post pointed out about the guy who burned his house
down).

Please do not assume that someone is not capable of understanding
things regarding TV and repairing it. With a little help and some
precautions (and common sense about electrical engineering), competent
people can repair TVs. Newsgroups like this one certainly helps.

I did not mean to offend collectively everyone (I was thinking no one
will read this posting because it was old. And only David and I will
scream at each other for a day and then forget about it). Obviously
that is not the case.

I am going to check yokes and sync signals. Hopefully, that will tell
me more about where to go. Thanks for all the help.

bharat

Hi...

Seeing as this message is a tiny bit apologetic, and a
lot less arrogant, I'll take a chance and try again...
hopefully a little has been learned (on both sides) and
a fresh start is possible.

I'll apologize for my message agreeing (sarcastically)
with you, and hope we can do better.

So, having said that, I'm an old stroke damaged
retired guy who hasn't been in the picture for
several years... just keeping in touch, so don't
take my word either as gospel, or current

What got everyone's dander up started with the yoke.
The yoke has absolutely nothing, repeat nothing to
do with your current problem. The yoke is that
round coils of wire on the neck of the picture tube,
pushed snugly up against the "flare" of the tube.
It's sole purpose in life is deflection. It's
driven by the horizontal and vertical ouputs.
If the horizontal portion fails, you'll be left
with (theoretically only) a bright white vertical
line. If the vertical fails, you'll be left with
(in reality) a straight white horizontal line across
the center of the crt.

So, let's leave the yoke out of it.

Sync is responsible for synchronizing that
vertical and horizontal deflection... failure
will give you a "rolling" picture (vertical fail)
or one that won't "stand straight up.

So let's leave sync out of it.

What have we left that IS perhaps responsible?

Well, there is a possibility that the blue grid
in the crt is shorted. This almost certainly makes
the set not worth repair.

There are drivers (transistors), one for each colour.
These are most likely located on the pcb which is
plugged onto the picture tube socket. The possiblity
is that one is shorted. Check them easily enough
by simply comparing them one against another with
the other "set"

Further than that I cannot go, not knowing your
set or even much of the state of the art.

But it's a start in the right direction, and perhaps
can lead to more.

I'll take a chance and give you one tiny little
lecture and life lesson. I raised many kids,
(all girls) and now am an old man all alone raising
(trying) a just turned teenage grand daughter.
I told each of them, and now I tell you, that how
you treat other people is going to make a bigger
difference in you life than any other thing you
can do. More important than education, than skills,
than wealth, than appearance, anything.

Let's see where we go from here.

Good luck, and take care.

Ken

 

[Leonard Caillouet]

Does the set still mute the video on ALL sources? 1080i? 480p? 480i? Do
you see any OSD, any PIP/POP?

Leonard

"bharat" <bhuva@vuse.vanderbilt.edu> wrote in message
news:27bb423c.0405050835.799dcef6@posting.google.com...

Now I am happy!!! And I agree I have a lot to learn about TV repair.
But with the help from the 'net, I should be able to get this one
working. Hopefully, I won't need to repair another one for a while.

Thanks to everyone who posted help.

I replaced the bad signal board with one from the functioning set.
The TV worked fine. Based on the hints from David and Ken, I think
the TV is going into Blue screen mute mode (the picture looks fine
whenever I could see it). I will check it based on responses from Ken
and David and see if I can get it working this weekend.

Sorry I lost my mind there earlier. When David posted that note saying
I do not have any business doing repairs on electronic systems, it got
my professional "ego" hurt (I guess) (specially because he did not
provide any help in that posting. In retrospect, he WAS proving help
by making sure I do not electrocute myself - without knowing my
background. But at the time, it didn't sound nice). I also
understand from Ken's posting why my statements would not make much
sense. I should have just stayed away from making any comments and
just asked for help. It would have saved a lot of bandwidth! Live
and learn!

Another reason for my temper-tantrum (I guess) was my old habits. I
used newsgroups extensively when I was a grad student. Then, we did
not post anything that was not useful (internet was not
available...only a few people had access to newsgroups. Bandwidth was
low). I always believed the postings were not for money or fame, but
for the satisfaction of helping others (same is true today. If any of
you who helped are waiting for a check from me, you will be waiting a
long time). When I saw David's post, it just irked me that he was
not telling me anything useful (I repeatedly stated in my postings
that if you can't help, stay away...I guess old habits die hard!).

Anyway, I like this newsgroup. I will start reading it on a regular
basis and see if I can provide help. I may not be a good
trouble-shooter, but I am a good designer. If you need help in the
design area, do drop a line.

bharat

 

[bharat]

None of the sources I checked worked. The screen stays blue. No PIP
either. Video is certainly (as far as I can tell) in blue screen mute
mode (never heard of this before...but then I am not an expert on
these matters!!!). I haven't checked CC input as per David. I
will check it tonight. RGB outputs on jungle IC are not what the
manual says they should be (staying HIGH most of the time as David
suggested).

Last night, I checked the voltages on the sync inputs on micro. The
H-Sync node on the micro is supposed to have 3.0V according to the
manual and it was showing 2.5 (my kids came back before I could check
it on oscilloscope...so had to give up). SCL1 and SDA1 (don't know
what these signals are...if you can post something about their
function, I will appreciate it) also are supposed to be 4.6V but were
showing around 4.0V. All these measurements are DC. Rest of signals
were showing expected (as per the schematic) voltages.

Can a 0.5V drop on H-sync cause blue_screen mute? I will have to
trace that one to see why that is low. Also, I will check all sync
signals on oscilloscope to check for proper waveforms. Is micro the
only circuit that will cause a blue-screen mute (BSM)? David had
listed a lot of reasons for BSM but only micro as the controller for
BSM. Another questions I have is how does the menu screen work if
sync signals are messed up? I thought all screen functions will be
needing sync signals and menu is certainly screen-based. Does this
mean sync are OK but something else is causing BSM or are menu sync
signals different from normal sync signals?

Gotta run....I gave my final and kids are lining up to know their
grades and I haven't graded the exams yet!!

Why does my posting take a lot longer (at least it seems to me that
way) than everyone else's posting? It seems David posted twice before
mine even showed up!

bharat

 

[John Miller]

bharat wrote:

Why does my posting take a lot longer (at least it seems to me that
way) than everyone else's posting? It seems David posted twice before
mine even showed up!

You're posting via Google; David is posting via greennet.net.

--
John Miller
Email address: domain, n4vu.com; username, jsm

Everyone's in a high place when you're on your knees.

 

[Ken Weitzel]

bharat wrote:

None of the sources I checked worked. The screen stays blue. No PIP
either. Video is certainly (as far as I can tell) in blue screen mute
mode (never heard of this before...but then I am not an expert on
these matters!!!). I haven't checked CC input as per David. I
will check it tonight. RGB outputs on jungle IC are not what the
manual says they should be (staying HIGH most of the time as David
suggested).

Last night, I checked the voltages on the sync inputs on micro. The
H-Sync node on the micro is supposed to have 3.0V according to the
manual and it was showing 2.5 (my kids came back before I could check
it on oscilloscope...so had to give up). SCL1 and SDA1 (don't know
what these signals are...if you can post something about their
function, I will appreciate it) also are supposed to be 4.6V but were
showing around 4.0V. All these measurements are DC. Rest of signals
were showing expected (as per the schematic) voltages.

Can a 0.5V drop on H-sync cause blue_screen mute? I will have to
trace that one to see why that is low. Also, I will check all sync
signals on oscilloscope to check for proper waveforms. Is micro the
only circuit that will cause a blue-screen mute (BSM)? David had
listed a lot of reasons for BSM but only micro as the controller for
BSM. Another questions I have is how does the menu screen work if
sync signals are messed up? I thought all screen functions will be
needing sync signals and menu is certainly screen-based. Does this
mean sync are OK but something else is causing BSM or are menu sync
signals different from normal sync signals?

Gotta run....I gave my final and kids are lining up to know their
grades and I haven't graded the exams yet!!

Why does my posting take a lot longer (at least it seems to me that
way) than everyone else's posting? It seems David posted twice before
mine even showed up!

bharat

Hi...

I believe you'll find that the law calls for ungraded
papers to all recieve the default A+, or 4, or 100%;
whichever is best in your country.

I have one more tiny suggestion if I may? Keep in
mind it comes from an "old hat" as David so generously
called it

I, too, had never seen a blue screen (except for
Windows) so played around a little. Big 5 bedroom
house for one old man and one little girl, but lots
of TV's...

All connected to cable boxes. Tried them.
Turn the cable box off via remote, and the TV
mutes audio, the raster goes very, very
dim for about 5 seconds; then the tv automagically
shuts off. (seperate ac feeds)

One in the basement belongs to my cottage
neighbor, waiting for transport to the cottage
for fishing season opening tomorrow.
Plugged it in - snow and hiss. Stuck a
resistor lead into the rf input, poor picture
and sound or snow and hiss on all channels.

Wondered why the difference, worried over it for
a while, and finally found the difference.

User menu - choose "cable" or "tv". The sets
upstairs set to cable; the one in the basement
set to tv.

So - is it possible that the set you're working
on in the cable position with no cable box?
(switching modules would have also switched
eproms, might have been different)

Worth a shot, anyway.

Good luck.

Ken

 

[r c]

I have een some great suggestions.
Here is mine.
start over.
use your 5 senses.
give it an extreme visual inspection,
smell the unit, .
feel the unit, etc
Then, check your power supplies, both main and local, ( in any
suspected areas)
Get the manual.
Use sympton analyisis diagnosis to narrow your troubleshooting.
If you have a PIP board, suspect that. (and or component therein)
Tuner possibly, and whatever video switching
devices/circuits would be suspect as well.
Looks like a possible "crap"-acitor hunt

...finals...
...kids...

those may play a role
good luck

 

[Leonard Caillouet]

Cable mode allows the set to recieve cable frequencies instead of the UHF
that the air or tv mode allows. It has nothing to do with whether the set
isconnected to a cable box or not on most sets.

Leonard

"Ken Weitzel" <kweitzel@shaw.ca> wrote in message
news:cwymc.367400$Pk3.158706@pd7tw1no...

bharat wrote:
None of the sources I checked worked. The screen stays blue. No PIP
either. Video is certainly (as far as I can tell) in blue screen mute
mode (never heard of this before...but then I am not an expert on
these matters!!!). I haven't checked CC input as per David. I
will check it tonight. RGB outputs on jungle IC are not what the
manual says they should be (staying HIGH most of the time as David
suggested).

Last night, I checked the voltages on the sync inputs on micro. The
H-Sync node on the micro is supposed to have 3.0V according to the
manual and it was showing 2.5 (my kids came back before I could check
it on oscilloscope...so had to give up). SCL1 and SDA1 (don't know
what these signals are...if you can post something about their
function, I will appreciate it) also are supposed to be 4.6V but were
showing around 4.0V. All these measurements are DC. Rest of signals
were showing expected (as per the schematic) voltages.

Can a 0.5V drop on H-sync cause blue_screen mute? I will have to
trace that one to see why that is low. Also, I will check all sync
signals on oscilloscope to check for proper waveforms. Is micro the
only circuit that will cause a blue-screen mute (BSM)? David had
listed a lot of reasons for BSM but only micro as the controller for
BSM. Another questions I have is how does the menu screen work if
sync signals are messed up? I thought all screen functions will be
needing sync signals and menu is certainly screen-based. Does this
mean sync are OK but something else is causing BSM or are menu sync
signals different from normal sync signals?

Gotta run....I gave my final and kids are lining up to know their
grades and I haven't graded the exams yet!!

Why does my posting take a lot longer (at least it seems to me that
way) than everyone else's posting? It seems David posted twice before
mine even showed up!

bharat

Hi...

I believe you'll find that the law calls for ungraded
papers to all recieve the default A+, or 4, or 100%;
whichever is best in your country.

I have one more tiny suggestion if I may? Keep in
mind it comes from an "old hat" as David so generously
called it

I, too, had never seen a blue screen (except for
Windows) so played around a little. Big 5 bedroom
house for one old man and one little girl, but lots
of TV's...

All connected to cable boxes. Tried them.
Turn the cable box off via remote, and the TV
mutes audio, the raster goes very, very
dim for about 5 seconds; then the tv automagically
shuts off. (seperate ac feeds)

One in the basement belongs to my cottage
neighbor, waiting for transport to the cottage
for fishing season opening tomorrow.
Plugged it in - snow and hiss. Stuck a
resistor lead into the rf input, poor picture
and sound or snow and hiss on all channels.

Wondered why the difference, worried over it for
a while, and finally found the difference.

User menu - choose "cable" or "tv". The sets
upstairs set to cable; the one in the basement
set to tv.

So - is it possible that the set you're working
on in the cable position with no cable box?
(switching modules would have also switched
eproms, might have been different)

Worth a shot, anyway.

Good luck.

Ken

 

[Leonard Caillouet]

PIP and capacitor problems have not been common issues with this set. This
guy needs to be using a scope at this point.

Leonard

"r c" <res_cogitans@webtv.net> wrote in message
news:27661-409B0445-747@storefull-3354.bay.webtv.net...

I have een some great suggestions.
Here is mine.
start over.
use your 5 senses.
give it an extreme visual inspection,
smell the unit, .
feel the unit, etc
Then, check your power supplies, both main and local, ( in any
suspected areas)
Get the manual.
Use sympton analyisis diagnosis to narrow your troubleshooting.
If you have a PIP board, suspect that. (and or component therein)
Tuner possibly, and whatever video switching
devices/circuits would be suspect as well.
Looks like a possible "crap"-acitor hunt

...finals...
...kids...


those may play a role
good luck

 

[Ken Weitzel]

Leonard Caillouet wrote:

Cable mode allows the set to recieve cable frequencies instead of the UHF
that the air or tv mode allows. It has nothing to do with whether the set
isconnected to a cable box or not on most sets.

Leonard

Hi Leonard...

Sounds like you might be in the same "old hat" category
as me. Give up, you can't win

That's the way I remember it too. First uhf which
of course was a whole different thing.

Then a mechanical switch which allowed the tuner
to go up to channel 99 or thereabouts in cable
position.

I expected now the same, with the tuner just going
even higher. Playing with the "connected to
nothing" set downstairs in cable position still
only allows channels 2 through 13. Same in both
positions.

Dunno. I'm waiting for my sons-in-law to help
me load it into the car for the trip to the
cabin - and the walleyes are waiting for our
ceremonial 12:01 am casts off the end of the
dock - grand daughter first, of course

Walleye filets for breakfast... have a good
weekend everyone.

Take care.

Ken

 

[David]

You need an oscilloscope and isolation transformer to diagnose the set. You
also need to understand what HOT ground and Signal ground are and where they
are located in the tv set for you scope ground (use the tuner shield).

H-sync will be at horizontal sweep frequency pulse, 15kHz or 32Khz
approximate, may be positive or negative going.
V-sync will be at vertical sweep rate of usually 60Hz.

The signal sync will be the combined vertical and horizontal sync with the
video information removed. This is the one you really need to look at.
Somewhere between the signal circuits and the system control.


"bharat" <bhuva@vuse.vanderbilt.edu> wrote in message
news:27bb423c.0405061156.2868de74@posting.google.com...

None of the sources I checked worked. The screen stays blue. No PIP
either. Video is certainly (as far as I can tell) in blue screen mute
mode (never heard of this before...but then I am not an expert on
these matters!!!). I haven't checked CC input as per David. I
will check it tonight. RGB outputs on jungle IC are not what the
manual says they should be (staying HIGH most of the time as David
suggested).

Last night, I checked the voltages on the sync inputs on micro. The
H-Sync node on the micro is supposed to have 3.0V according to the
manual and it was showing 2.5 (my kids came back before I could check
it on oscilloscope...so had to give up). SCL1 and SDA1 (don't know
what these signals are...if you can post something about their
function, I will appreciate it) also are supposed to be 4.6V but were
showing around 4.0V. All these measurements are DC. Rest of signals
were showing expected (as per the schematic) voltages.

Can a 0.5V drop on H-sync cause blue_screen mute? I will have to
trace that one to see why that is low. Also, I will check all sync
signals on oscilloscope to check for proper waveforms. Is micro the
only circuit that will cause a blue-screen mute (BSM)? David had
listed a lot of reasons for BSM but only micro as the controller for
BSM. Another questions I have is how does the menu screen work if
sync signals are messed up? I thought all screen functions will be
needing sync signals and menu is certainly screen-based. Does this
mean sync are OK but something else is causing BSM or are menu sync
signals different from normal sync signals?

Gotta run....I gave my final and kids are lining up to know their
grades and I haven't graded the exams yet!!

Why does my posting take a lot longer (at least it seems to me that
way) than everyone else's posting? It seems David posted twice before
mine even showed up!

bharat