Toshiba TV29C90 problem; Image fades to black...

[Sylvia Else]

On 15/03/2011 4:12 PM, kreed wrote:

On Mar 15, 2:42 pm, Sylvia Else<syl...@not.here.invalid> wrote:
On 15/03/2011 10:33 AM, b wrote:

Sony tvs are notorious for being picky about spares. I dislike them
for that reason, as they usually get repair estimates rejected due to
cost grounds.And that's assuming spares availability...

I recently dumped a 25" CRT set (FE2 chassis I think) - shorted
horizontal output stage. Common fault with the chassis - the
transformer fails, killing the line o/p transistor and damages the
micro. Unless you replace the lot in one go, with genuine sony bits,
you're back to square one... plus the uPc is NLA and an awkward smd
type. Set was BER, a shame considering it was barely 8 years old.
-B

That's the kind of scenario that's deterred me from replacing the
transistor. Your comment about the damage to the microprocessor is
particularly relevant given my inability to persuade the set to produce
sound with the transistor removed, or even to enter/leave standby mode.

Sylvia.

Not familiar with the set so I don't know exactly - but functions
related to sound may
be powered from a rail generated from the EHT transformer.

Even if not, it is possible that it may be muted or disabled by the
CPU if the EHT circuit isn't working correctly.

Or just to make the damned thing difficult to diagnose, thus increasing
the chance it'll be tossed and a new one bought.

Many other functions may be shut off for safety also.

In the past I have found that the majority of sets/monitors (note -
have not worked on many newer than the 1990's)
will work once the H out transistor is replaced, however this isn't
always the case. The tuning caps (usually across the transistor) can
fail or lose capacitance causing the voltage to go through the roof
(they often look normal),
yokes can burn out (Samsung, usually inside on the H section where you
can't see it without removing from tube, usually from corrosion), the
EHT transformer can short internally, or can develop an arc through
the plastic casing to chassis.

Arcing from out of the housing on some transformers that contains the
focus and screen pots. I have seen often

Some of these arcs can be particularly bad, in fact some seem to
manage to burn their way through silicon sealant and continue the arc
as before. (note -too close to the frame to allow a decent thickness)

In some cases, the only way I could stop this was to remove the
aluminium frame from around the transformer, and cut away a section of
it near the where the arc was so as to give the transformer nothing to
arc to. It also allowed more clearance for a thicker coat of silcone
sealant to prevent future problems.



I am leaving out things like dry joints and obviously damaged
components as I assume most people on this group would look for these
before posting.

At one point, I saw some of the smoke escape, but unfortunately was on
the wrong side of the set to see where it came from

Sylvia.

 

[Sylvia Else]

On 15/03/2011 10:46 PM, kreed wrote:

One big thing that would bother me, is paying for and replacing the
transistor, and then finding the problem still there or other faults.
You could change the CPU and god knows what else in between and still
have a problem.

And indeed discover that the still existing fault destroys them again.

TO make matters
worse, it looked as though the FET was designed to put a dead short
across the batteries under some circumstance.

No fuse protecting the battery? Sounds like a serious safety issue -
shorting out lead-acid batteries would have to be good way of starting
fires.

Sylvia.

 

[kreed]

On Mar 15, 6:23 pm, Sylvia Else <syl...@not.here.invalid> wrote:

On 15/03/2011 4:12 PM, kreed wrote:



On Mar 15, 2:42 pm, Sylvia Else<syl...@not.here.invalid>  wrote:
On 15/03/2011 10:33 AM, b wrote:

Sony tvs are notorious for being picky about spares. I dislike them
for that reason, as they usually get repair estimates rejected due to
cost grounds.And that's assuming spares availability...

   I recently dumped a 25" CRT set (FE2 chassis I think) - shorted
horizontal output stage. Common fault with the chassis - the
transformer fails, killing the line o/p transistor and damages the
micro. Unless you replace the lot in one go, with genuine sony bits,
you're back to square one... plus the uPc is NLA and an awkward smd
type. Set was BER, a shame considering it was barely 8 years old.
-B

That's the kind of scenario that's deterred me from replacing the
transistor. Your comment about the damage to the microprocessor is
particularly relevant given my inability to persuade the set to produce
sound with the transistor removed, or even to enter/leave standby mode..

Sylvia.

Not familiar with the set so I don't know exactly - but functions
related to sound may
be powered from a rail generated from the EHT transformer.

Even if not, it is possible that it may be muted or disabled by the
CPU if the EHT circuit isn't working correctly.

Or just to make the damned thing difficult to diagnose, thus increasing
the chance it'll be tossed and a new one bought.

Years ago they probably realised that the sets were likely to last x
number of years, and by that time, few would bother fixing. Once you
start using tiny surface mount parts (including those QFP chips) the
odds of people not bothering with a repair increase exponentially
along with the cost if they do pay a serviceman to do it. Robot
assembly also allows things to be packed tighter than manual
assembly ?

At the same time the costs of these sets have plummeted. Can remember
around 2000 buying a new 25" set, and was over $1000. Within 3 years
or so, they were down around $5-600, and now if you can still buy 25"
CRT sets, I would be surprised if they were even $150-$200 in discount
stores or similar. I doubt you would get a repair done for a fault
like yours for less than this at a TV service shop. We have 2 nice
Sharp 26" ones in the Garage, that work fine and wont get used by me.
Cant even give them away.


Interesting that that link to a manual that was posted really only
shows how to change the tube, yoke chassis, front plastic push button
assembly - but no schematic or details on board level repair. Maybe
they would just send exchange boards during the warranty period.

One big thing that would bother me, is paying for and replacing the
transistor, and then finding the problem still there or other faults.
You could change the CPU and god knows what else in between and still
have a problem.

Many other functions may be shut off for safety also.

In the past I have found that the majority of sets/monitors (note -
have not worked on many newer than the 1990's)
will work once the H out transistor is replaced, however this isn't
always the case.  The tuning caps (usually across the transistor) can
fail or lose capacitance causing the voltage to go through the roof
(they often look normal),
yokes can burn out (Samsung, usually inside on the H section where you
can't see it without removing from tube, usually from corrosion), the
EHT transformer can short internally, or can develop an arc through
the plastic casing to chassis.

Arcing from out of the housing on some transformers that contains the
focus and screen pots. I have seen often

Some of these arcs can be particularly bad, in fact some seem to
manage to burn their way through silicon sealant and continue the arc
as before. (note -too close to the frame to allow a decent thickness)

In some cases, the only way I could stop this was to remove the
aluminium frame from around the transformer, and cut away a section of
it near the where the arc was so as to give the transformer nothing to
arc to. It also allowed more clearance for a thicker coat of silcone
sealant to prevent future problems.

I am leaving out things like dry joints and obviously damaged
components as I assume most people on this group would look for these
before posting.

At one point, I saw some of the smoke escape, but unfortunately was on
the wrong side of the set to see where it came from

And short of going over everything with a magnifier and strong light
you have buckleys chance
of finding it - even that probably wouldnt work.

Had the same recently with a Eaton Powerware UPS. Smoke came out, the
thing still "sort of worked" .

Couldnt find the smoke source but found a number of burnt tracks,
shorted out 5404 3A diodes, and a FET that was shorted on all 3 legs,
the part was unobtainable from regular sources. TO make matters
worse, it looked as though the FET was designed to put a dead short
across the batteries under some circumstance. The battery was also
practically dead.

Getting another unit for about $110 ended up being the best fix.

> Sylvia.

 

[Sylvia Else]

On 15/03/2011 11:35 PM, kreed wrote:

The thing that probably killed it was that I was using it to charge up
about 5 SLA batteries, one after the other, and it might not have been
designed to be charging for this length of time continuously. once the
5th battery was connected - smoke time.

Still, I'd have expected it to have reached thermal equilibrium long
before even the first battery was fully charged. It shouldn't get any
hotter from subsequent chargings.

Sylvia.

 

[b]

On Mar 15, 12:46 pm, kreed <kenreed1...@gmail.com> wrote:

One big thing that would bother me, is paying for and replacing the
transistor, and then finding the problem still there or other faults.
You could change the CPU and god knows what else in between and still
have a problem.

This brings us back to the Sony problem. On many sets you can use
standard transistors and other semiconductors, at least for test
purposes, so it is usually worth a punt for a few quid to see if it
fixes the set. But an expensive chain failure which necessitates the
use of genuine parts (a typical sony scenario!) means that these sets
are not often worth bothering with. In this case I had no idea of the
set's history, for all I know the tube could have been wasted too -
another reason not to put serious time and money into such an item.

It is ironic that latterday CRT 'supermarket sets' tend to have a
better chance of getting fixed than some of those costing several
times as much!
-B

 

[kreed]

On Mar 15, 9:56 pm, Sylvia Else <syl...@not.here.invalid> wrote:

On 15/03/2011 10:46 PM, kreed wrote:

One big thing that would bother me, is paying for and replacing the
transistor, and then finding the problem still there or other faults.
You could change the CPU and god knows what else in between and still
have a problem.

And indeed discover that the still existing fault destroys them again.

 > TO make matters

worse, it looked as though the FET was designed to put a dead short
across the batteries under some circumstance.

No fuse protecting the battery? Sounds like a serious safety issue -
shorting out lead-acid batteries would have to be good way of starting
fires.

Sylvia.

From memory, and I may be wrong - It was not protected by the fuse,
only by the blown PCB tracks. (and there was current limiting from
there being a relatively thin wire leading from the battery + to this
part of the circuit.)

The circuit was not easy to trace out, and parts like this seemed
illogical.

The thing that probably killed it was that I was using it to charge up
about 5 SLA batteries, one after the other, and it might not have been
designed to be charging for this length of time continuously. once the
5th battery was connected - smoke time.

 

[Wild_Bill]

The set's inability to show any signs of working circuits, with the HOT
(transistor) removed (or failed), is normal for most TVs made within about
the last 25 years.

Other than a Standby voltage supply, most TVs won't operate (even partially)
without a functioning horiz scan/sweep circuit, as in general, several
voltage supplies are derived from the IHVT integrated high voltage
transformer (some refer to as flyback or other terms).

--
Cheers,
WB
..............


"Sylvia Else" <sylvia@not.here.invalid> wrote in message
news:8u891oFqceU1@mid.individual.net...

That's the kind of scenario that's deterred me from replacing the
transistor. Your comment about the damage to the microprocessor is
particularly relevant given my inability to persuade the set to produce
sound with the transistor removed, or even to enter/leave standby mode.

Sylvia.

 

[William Sommerwerck]

The set's inability to show any signs of working circuits, with
the HOT removed (or failed), is normal for most TVs made
within about the last 25 years.

Other than a Standby voltage supply, most TVs won't operate
(even partially) without a functioning horiz scan/sweep circuit,
as in general, several voltage supplies are derived from the IHVT
integrated high voltage transformer (some refer to as flyback or
other terms).

My Sony KV-1920, purchased ca. 1974, was one of the first TVs with a
switching power supply. When the supply failed in the early 80s, a guy from
Sony warned me not to try to fix it myself. "If you don't catch all the bad
parts the first time, some of the replacement parts might fail. It's best to
have a trained tech look at it." It cost me around $75 (which seemed a lot,
then) but the set was properly repaired and worked another 15 years.

 

[Meat Plow]

On Mon, 14 Mar 2011 18:29:09 -0700, Stroonz wrote:

On Mar 14, 8:01 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

** I have seen them with 20 ohms and less.


******** Yes, but those are called shorted.



On Mar 14, 8:01 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
** Not all HOT drive circuits are like that.


******** She didn't ask about all HOT drive circuits, she asked about
HERS.



** Why don't you go and get fucked ?

......  Phil

Now is that nice?

You can safely ignore Phil's posts. Most do because of his extreme mood
swings and personality disorder.



--
Live Fast Die Young, Leave A Pretty Corpse

 

[kreed]

On Mar 15, 11:00 pm, Sylvia Else <syl...@not.here.invalid> wrote:

On 15/03/2011 11:35 PM, kreed wrote:



The thing that probably killed it was that I was using it to charge up
about 5 SLA batteries, one after the other, and it might not have been
designed to be charging for this length of time continuously. once the
5th battery was connected - smoke time.

Still, I'd have expected it to have reached thermal equilibrium long
before even the first battery was fully charged. It shouldn't get any
hotter from subsequent chargings.

Sylvia.

You are probably right, but this was the only change to "normal" usage
I can think of before it failed

 

[Stroonz]

On Mar 15, 11:47 am, Meat Plow <mhyw...@yahoo.com> wrote:

You can safely ignore Phil's posts. Most do because of his extreme mood
swings and personality disorder.

--

On a hunch, I checked the garbage AOL email addy that I use to
register for public forums, and there (amongst the ton of spam emails)
were more than a couple of emails offering the same advice. But I'm
not completely convinced he has mood swings or a personality disorder;
I suspect he's a typical internet bully who can only demonstrate
bravery from behind the security of a keyboard. If someone were to
act like that in real life, you go up to them, grab them by the
throat, and watch them fill their Pampers. Still, I've often gotten a
good laugh from his posts.

 

[Phil Allison]

"Stroonz is a CUNT "


I suspect he's a typical internet bully ..


** Hey - pal.

Blind Freddy can see that YOU are bullying me.

Cos you are a psychotic control freak.



..... Phil

 

[Sylvia Else]

On 16/03/2011 8:55 AM, kreed wrote:

On Mar 15, 11:00 pm, Sylvia Else<syl...@not.here.invalid> wrote:
On 15/03/2011 11:35 PM, kreed wrote:



The thing that probably killed it was that I was using it to charge up
about 5 SLA batteries, one after the other, and it might not have been
designed to be charging for this length of time continuously. once the
5th battery was connected - smoke time.

Still, I'd have expected it to have reached thermal equilibrium long
before even the first battery was fully charged. It shouldn't get any
hotter from subsequent chargings.

Sylvia.

You are probably right, but this was the only change to "normal" usage
I can think of before it failed

Coincidence - there's probably a yet to be discovered perverse law of
nature that says that a machine is most likely to fail shortly after a
totally irrelevant change in the way it is used.

Sylvia.

 

[Sylvia Else]

On 16/03/2011 2:19 AM, Wild_Bill wrote:

The set's inability to show any signs of working circuits, with the HOT
(transistor) removed (or failed), is normal for most TVs made within
about the last 25 years.

Other than a Standby voltage supply, most TVs won't operate (even
partially) without a functioning horiz scan/sweep circuit, as in
general, several voltage supplies are derived from the IHVT integrated
high voltage transformer (some refer to as flyback or other terms).

Well, that's possible, though as I've indicated, my TV wouldn't even
enter standby mode.

I suppose it's conceivable that since it failed in operation, it always
tries to power up in that mode, and that the processor won't allow entry
to standby mode unless everything's working. That would seem a bit
perverse, but who knows?

Sylvia.

 

[William Sommerwerck]

Coincidence - there's probably a yet to be discovered
perverse law of nature that says that a machine is most
likely to fail shortly after a totally irrelevant change in the
way it is used.

Here's another one... "A machine is most likely to irreversibly fail shortly
after you've gone to a great deal of trouble to fix it."

 

[Wild_Bill]

These types of failures are the kinds of problems that TV techs have seen
regularly for a lot of years.. a relatively simple fault is capable of
causing the "smart chassis" type designs to be completely dead, in many
cases.

In sets that develop a fault, and also have some other components that have
changed values due to age, the chassis essentially has compound faults,
which were commonly referred to as Tough Dogs, among other names.
Shut-down circuits have been implemented for many years, to prevent the TV
from operating at all, if the CRT's HV potential exceeded a limit, as a
safety shutdown.

Some minor faults are often complicated by poor soldering during the circuit
board manufacturing process/build, which creates new faults as the boards
age and go thru many thermal cycles.

Many of the electronic equipment designs presently manufactured are similar
designs of smart chassis design, in that one fault will disable every
function.. maybe with the exception of a blinking LED.
In many of these designs, either everything operates within normal limits,
or the units just shut down and won't restart without experienced technical
intervention.

--
Cheers,
WB
..............


"Sylvia Else" <sylvia@not.here.invalid> wrote in message
news:8uaf1cFp84U1@mid.individual.net...

I suppose it's conceivable that since it failed in operation, it always
tries to power up in that mode, and that the processor won't allow entry
to standby mode unless everything's working. That would seem a bit
perverse, but who knows?

Sylvia.

 

[William Sommerwerck]

In sets that develop a fault, and also have some other
components that have changed values due to age, the
chassis essentially has compound faults, which were
commonly referred to as Tough Dogs, among other names.

The term probably dates back to at least the 30s. It refers to a problem
that refuses to yield to common-sense analysis or trouble-shooting.

 

[Meat Plow]

On Tue, 15 Mar 2011 15:20:51 -0700, Stroonz wrote:

On Mar 15, 11:47 am, Meat Plow <mhyw...@yahoo.com> wrote:


You can safely ignore Phil's posts. Most do because of his extreme mood
swings and personality disorder.

--

On a hunch, I checked the garbage AOL email addy that I use to register
for public forums, and there (amongst the ton of spam emails) were more
than a couple of emails offering the same advice. But I'm not
completely convinced he has mood swings or a personality disorder; I
suspect he's a typical internet bully who can only demonstrate bravery
from behind the security of a keyboard. If someone were to act like
that in real life, you go up to them, grab them by the throat, and watch
them fill their Pampers. Still, I've often gotten a good laugh from his
posts.

I've had dialog with Phil that was very helpful and he's even apologized
to me (in his own way) once. On other occasions he's tore into me for no
reason whatsoever. And it's not just me but others that don't do things
the Phil Allison Way. I have no official proof but this behavior smacks
of a sever mental disorder.


--
Live Fast Die Young, Leave A Pretty Corpse

 

[bz]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:ilp3r9$p3i$1@news.eternal-september.org:

Coincidence - there's probably a yet to be discovered
perverse law of nature that says that a machine is most
likely to fail shortly after a totally irrelevant change in the
way it is used.

Here's another one... "A machine is most likely to irreversibly fail
shortly after you've gone to a great deal of trouble to fix it."

It is called "the innate perversity of inanimate matter".
There was an article on it published MANY years ago in CQ magzine.

It have some ways to use ipoim to do things around the ham shack.
1) in order to prevent stretching from detuning your antenna, cut the wire
short to allow for stretch.
2) to fix a complex electronic device:
a) go through the parts list and contact all the parts suppliers. You
will find one or two parts that can not be found anywhere; it is one of
those.
b) examine the layout and locate the part that is most difficult to
remove and replace. You just found your defective component.

I don't remember the rest of the article but it has proven to be quite
useful to me, over the years.

73 de N5bz

 

[Neid Koffe]

Att: Frank

Got given this coffee machine.
Aroma Coffee™ 12 Digital (PC4700)

Fault:

When powering it on (digital panel) it turns straight off and the
element never gets to heats up.

This digital panel I assume control the usage etc. But also
controls the On/Off. The buttons themselves seem functional.
I can hear a relay trip once when it turns it self off again.

I've pulled to bits to check for obvious problems.
I'm thinking I'm looking at a round Thermistor (see below links)
that attaches directly to the element and it appears wired to the
mains voltage (230-240v here) on the power/relay board on the
right
side of the photo.

That's a thermal switch, not a thermistor. It should be closed.
- Franc Zabkar

Thanks for the reply...

So that is normally closed at all times unless it hits the temp
threshold? Even in a no power state?

How would it be acting if faulty?