Weirdest problem

[Barbara]

I have a solid-state TV receiver Samsung model TOD1841 13" color
receiver about 7 or 8 years old.
with remote control. which has functions like alarm, scheduled turn off etc
(irrelevant for the
issue here but just describing the state of the art on it)

I can turn it ON & it works ok until I turn it OFF ( either manually or
with remote ) .
Then I cannot turn it ON for at least what seems like about 48 hours.
Then the same cycle repeats

Has anyone seen this ? So weird ?

 

[.Bill]

I have a solid-state TV receiver Samsung model TOD1841 13" color
receiver about 7 or 8 years old.
with remote control. which has functions like alarm, scheduled turn off etc
(irrelevant for the
issue here but just describing the state of the art on it)

I can turn it ON & it works ok until I turn it OFF ( either manually or
with remote ) .
Then I cannot turn it ON for at least what seems like about 48 hours.
Then the same cycle repeats

Has anyone seen this ? So weird ?

The most effective solution can be had for about $119 at most big retail
places. All new parts, no dust, a warranty of sorts, no effort and it
will work.
Now if you are a hobbyist maybe you have an endless cost limit for
learning something new.
I hate to promote the "throw-away society" but maybe you should write a
letter to the factory commending them about how this set lasted 7 years.
Well, maybe not because that would further encourage them.
Seven years out of a 13" Samsung set ain't so bad.

-BM

 

[Barbara]

Obviously I did not make it clear
From an electronics standpoint I am very curious

 

[Joseph Hansen]

Are you unable to turn it on using the remote and the front panel button, or
is the problem present only when using the remote?
Have you tried unplugging it after turning off and waiting a few minutes
before plugging back in? Does that make any difference?
I suppose it could be a case of a cap charging that is supposed to discharge
through a resistor, but the resistor is open... or something like that. If
so, there's a chance the damage will be visible when you look at the board.
It could also be something heating up, and opening or shorting, and it has
to cool down before going back to it's working state. Once again, this
could be visible, or you might find it by poking around with a LONG wooden
stick... pushing on various components GENTLY might cause it to start
working again by closing the gap. Whichever component you are prodding when
it starts working again is probably the bad part.
Can't get any more specific without looking at it myself.

 

[Steve Sousa]

Weird and involving time problems usually mean one thing: Bad capacitor(s).
Check all electrolitics for swelling and ac ripple. Hint: start with the
400V mains rectifier.


Steve

 

[Roderick Stewart]

Weird and involving time problems usually mean one thing: Bad capacitor(s).

Nonsense. This situation is absolutely screaming that it is a thermal problem
of some sort. Something works when it is cold, but doesn't work when it is
hot. Something that is required to trigger the power supply into life, though
without a service manual and appropriate measuring instruments, it would be
difficult to suggest what.

Check all electrolitics for swelling and ac ripple. Hint: start with the
400V mains rectifier.

What sort of a "capacitor" is a "400V mains rectifier"?

The best advice here is from the person who suggested buying a new TV. For a
small screen TV that is 7 years old, repir wouldn't be worth the cost or the
bother. Above all, IF YOU DON'T KNOW EXACTLY WHAT YOU ARE DOING, DON'T MESS
WITH THE INSIDES OF A TV SET. YOU COULD ELECTROCUTE YOURSELF, OR BY FITTING
THE WRONG COMPONENTS YOU COULD CAUSE SOMETHING TO OVERHEAT AND START A FIRE.
(No apologies for the capitals).

Rod.

 

[Barbara]

Are you unable to turn it on using the remote and the front panel button, or
is the problem present only when using the remote?

Same in either case (meaning the remote control in NOT the problem)

Have you tried unplugging it after turning off and waiting a few minutes
before plugging back in?

Yes. I also tried the TV in different rooms

Does that make any difference?

No

 

[Barbara]

What sort of a "capacitor" is a "400V mains rectifier"?

May be he is referri to input rectifier circuit

http://www.tvdiagrams.com/help/h-ps.html

The electrolytics caps may have a hating issue
So you may both be right

The best advice here is from the person who suggested buying a new TV. For a
small screen TV that is 7 years old, repir wouldn't be worth the cost or the
bother. Above all, IF YOU DON'T KNOW EXACTLY WHAT YOU ARE DOING, DON'T MESS
WITH THE INSIDES OF A TV SET. YOU COULD ELECTROCUTE YOURSELF, OR BY FITTING
THE WRONG COMPONENTS YOU COULD CAUSE SOMETHING TO OVERHEAT AND START A FIRE.
(No apologies for the capitals).

Rod.

Never hurts to be reminded of safety.
I would add that , you better use a glove & grounding.

However unless you are messing with the PS , I would tend to think the DC
volts should be low
Except may be you are messing with the flyback transformer ?

 

[Barbara]

Flaky shutdown circuit ?
http://www.tacpservice.toshiba.com/TACP/media/pdf/TSQSTG005.pdf

 

[Jerry G.]

There are some parts that have become thermal sensitive. With the proper
procedures and set-up this can be serviced by an experienced technician.
But, it would not be cost effective, considering that this is a low cost TV
set.

I would not recommend for you to service this yourself. Without the proper
training, and set-up you will not get very far on your own, unless you are a
good guesser at changing parts.

There are some very serious safety issues when venturing in to a TV set.
There is the chance of injury, and if changing parts improperly, there is
the chance of a safety hazard when using the set.

--

Jerry G.
=====


I have a solid-state TV receiver Samsung model TOD1841 13" color
receiver about 7 or 8 years old.
with remote control. which has functions like alarm, scheduled turn off etc
(irrelevant for the
issue here but just describing the state of the art on it)

I can turn it ON & it works ok until I turn it OFF ( either manually or
with remote ) .
Then I cannot turn it ON for at least what seems like about 48 hours.
Then the same cycle repeats

Has anyone seen this ? So weird ?

 

[Joseph Hansen]

button,

Same in either case (meaning the remote control in NOT the problem)


Yes. I also tried the TV in different rooms


No

So, you could try the pushing with a stick trick. Or possibly inspection
will show the problem. If neither of these methods hands you the problem,
then like most of the others are saying, it will probably not be cost
effective for you to try to repair. Just get a new set. And do be careful
when poking around in the back of a tv set. Those who warned about
electrocuting yourself were not kidding. Even when a set is turned off and
unplugged for a long time, there can still be capacitors with a few hundred
volts stored on them to give the unwary finger a nasty jolt. And the
picture tube can have several thousand volts, although most modern tv's have
a resistor to drain that voltage built right into the flyback transformer.
If that resistor happens to be open, then the charge will stay until you
provide a path for discharge with your body... sometimes fatal, and never
comfortable.

 

[Fred Bloggs]

I have a solid-state TV receiver Samsung model TOD1841 13" color
receiver about 7 or 8 years old.
with remote control. which has functions like alarm, scheduled turn off etc
(irrelevant for the
issue here but just describing the state of the art on it)

I can turn it ON & it works ok until I turn it OFF ( either manually or
with remote ) .
Then I cannot turn it ON for at least what seems like about 48 hours.
Then the same cycle repeats

Has anyone seen this ? So weird ?

This TV most likely uses a relay to activate the power supply- and it is
sticking. A simple meter check of the line input VAC distribution will
confirm this. You know that it has to "keep alive" at least the IR
receiver for the remote commands to accept ON/OFF. Locate that relay-
find out how the IR controls it and see if this isn't the case. Just use
common sense like removing any jewelry, using clip leads, reaching into
set with only hand etc....when you work on the thing. It's hard to kill
yourself with a TV due to lack of intelligence- just look at all the
ones screaming about !!!SAFETY!!! as living proof-)

 

[Activ8]

This TV most likely uses a relay to activate the power supply- and it is
sticking. A simple meter check of the line input VAC distribution will
confirm this. You know that it has to "keep alive" at least the IR
receiver for the remote commands to accept ON/OFF. Locate that relay-
find out how the IR controls it and see if this isn't the case. Just use
common sense like removing any jewelry, using clip leads, reaching into
set with only hand etc....when you work on the thing. It's hard to kill
yourself with a TV due to lack of intelligence- just look at all the
ones screaming about !!!SAFETY!!! as living proof-)

OTOH, if during that period of time where it doesn't turn on, you
can hear said relay click on and shut off, the xray detect circuit
may be fouling up in some weird way that I haven't experianced,
though the relay prob *does* nmake more sense, IMO.

 

[Kevin G. Rhoads]

Never hurts to be reminded of safety.

I would add that , you better use a glove & grounding.

However unless you are messing with the PS , I would tend to think the DC
volts should be low
Except may be you are messing with the flyback transformer ?

Entire outside of picture tube may be, and much of it will be,
connected to rectified HV from flyback. If B&W 10-15kV, if
color, at least 22kV and probably closer to 30kV or more when
operating. HV caps likely not fully discharged when beast is off.

Add that cheap appliances often have AC mains come in w/o
transformer...

1) treat as High Voltage issue:
a) one hand rule (only use one hand at a time, keep other in pocket or behind back)
b) lone worker rule (NEVER work alone on HV, even unenergized circuits)
c) short out HV caps before proceeding and KEEP SHORTED during process

above are specific recommendations above and beyond normal safety rules

N.B., these procedures should be followed even if all you are doing is
taking the cover off and peering into to !@#$%^ thing

Take a lesson from the aviation community:
There are OLD pilots
and there are BOLD pilots
but there are NO OLD, BOLD pilots.

DO NOT TRUST GLOVES to keep you insulated from HV.

 

[Jan Panteltje]

OTOH, if during that period of time where it doesn't turn on, you
can hear said relay click on and shut off, the xray detect circuit

????????????Xray detector???
In a TV??????
What planet are you from?
JP

 

[Mark Kent]

Never hurts to be reminded of safety.
I would add that , you better use a glove & grounding.

However unless you are messing with the PS , I would tend to think the DC
volts should be low
Except may be you are messing with the flyback transformer ?

Ummm dangerous assumptions. When televisions glowed inside, they were all
'live chassis', which means there was a 50% chance that the chassis itself
was at mains potential (which was 240vac here).

More recent designs using SMPS (which were pioneered in TVs before appearing
in huge numbers in computers, later) would often have no isolation transformer
as such, so the chassis could still be at a potential of mains -x volts. Here's
a brief summary of why:

http://www.penders.cwc.net/otpsupps.html

If you're not sure, I'd suggest you leave well alone, these devices really
can kill you. If you are sure, then get a circuit diagram, preferably
a service manual, appropriate test equipment, a mains isolation transformer,
and have fun.

 

[Tom MacIntyre]

????????????Xray detector???
In a TV??????
What planet are you from?
JP

What does XRDet stand for in a television schematic, then?

Tom

 

[Roderick Stewart]

Entire outside of picture tube may be, and much of it will be,
connected to rectified HV from flyback.

Entire outside of picture tube will be earthed. It's the *inside* that
carries the high voltage.

"A little learning is a dangerous thing".

Rod.

 

[Roderick Stewart]

May be he is referri to input rectifier circuit

Then why not say so? A rectifier isn't a capacitor, and a capacirtor isn't a
rectifier. If you think I'm being pedantic to worry about the distinctions
between different electronic components, that's nothing to the behaviour of
the circuitry itself. If you wire up the wrong components in the wrong way it
simply won't work.

The electrolytics caps may have a hating issue
So you may both be right

Yes, sometimes I hate them too.

Seriously, the most common problem with electrolytics is that the electrolyte
dries up and the component goes low in value. the big ones in the power supply
going low like this would probably result in mains hum - light or dark bars
slowly drifting up and down the screen, or audible 50Hz/60Hz hum from the
loudspeaker.

[...]

However unless you are messing with the PS , I would tend to think the DC
volts should be low
Except may be you are messing with the flyback transformer ?

You can get yourself killed thinking like that. Unless you are familiar with
the innards of that particular design of TV set, you have no way of knowing
which bits of circuit are carrying lethal voltages and which aren't. Some
parts of the circuit will be perfectly safe to work on, even while the set is
switched on, PROVIDED YOU KNOW WHAT YOU ARE DOING. Others most certainly are
not, and if you don't know which they are, you should leave well alone.

Rod.

 

[Jim Thompson]

What does XRDet stand for in a television schematic, then?

Tom

X-rays aren't actually detected... there's just a clamp *separate*
from the HV regulator to keep voltages from getting to the X-ray
emission level if the HV regulator circuitry fails.

There's generally also a spark gap in there. I've seen them get
crudded up and kill the HV.

[Raised in a TV repair shop]

...Jim Thompson