Help with a fault ????

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Hi all,

I am hoping someone here may be able to help me with solving an intermittent
fault with our family TV....... PLEASE ?.
It is a Phillips 21PT2012 / 79R  and has what I think is the serial number
of BZ000231  723707  on the back cover.
The fault manifests itself as sudden loss of all picture, and light from the
screen and loss of sound at the same time, anywhere from 5 seconds to a few
minutes from switch on.
This started a week or so ago, and a turn off seemed to fix it, and now it
will not run longer than a minute or so without dying. It seems like the HT
supply drops out suddenly,
but as I understand it the power supply rails for all the circuitry on this
type of appliance may very well all come from one switching supply, and a
fault there could wipe out everything?
I have a reasonable understanding of electronics, and a good Fluke
multimeter, but no cct. diagram, and no experience with TVs.  Any
suggestions? I think that the set is about 4 years old, and I guess it must
be some component that is built to a commercial standard starting to break
down, but I was hoping that there may be hope rather than junking it?
Thanks for any assistance.

Tim





Re: Help with a fault ????


I did a google search on the serial number and go nowhere sorry I can not
help more at this moment.



TELL US THE CHASSIS NUMBER THAT SHOULD BE ON THE BACK OF THE SET
Have you taken the f$$$$$$ back off the set and seen if the heater still
run, or give us more of a clue, come on do a bit more than just tell the
useless serial number.


Hi all,

I am hoping someone here may be able to help me with solving an intermittent
fault with our family TV....... PLEASE ?.
It is a Phillips 21PT2012 / 79R  and has what I think is the serial number
of BZ000231  723707  on the back cover.
The fault manifests itself as sudden loss of all picture, and light from the
screen and loss of sound at the same time, anywhere from 5 seconds to a few
minutes from switch on.
This started a week or so ago, and a turn off seemed to fix it, and now it
will not run longer than a minute or so without dying. It seems like the HT
supply drops out suddenly,
but as I understand it the power supply rails for all the circuitry on this
type of appliance may very well all come from one switching supply, and a
fault there could wipe out everything?
I have a reasonable understanding of electronics, and a good Fluke
multimeter, but no cct. diagram, and no experience with TVs.  Any
suggestions? I think that the set is about 4 years old, and I guess it must
be some component that is built to a commercial standard starting to break
down, but I was hoping that there may be hope rather than junking it?
Thanks for any assistance.

Tim






Re: Help with a fault ????


Hi,

To be honest you are better off getting it to the technician.
Philips TVs are generally difficult to fix. Lots of the times problems are
quite weird, especially in newer sets.

If you never worked on TV -- IT IS DANGEROUS AND CAN KILL YOU!!!!!! It does
not matter how experienced you are with electronics.

Does TV flashes red light when fault occurs?
Does Tv reacts to a mechanical shock?

How is B+ when running and when fault occurs?
I would check horizontal stage, especially HV caps for the sign of stress.
Also I would try to run power supply on dummy load to isolate power supply.

Rudolf
P.S. If in Melbourne, I can take a look at it

It may be anything really. One of teh first steps

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Re: Help with a fault ????



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Always worth inspecting the soldering - most likely lead free solder and
inherently unreliable!



Re: Help with a fault ????



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First up, be aware that inexperience and TV repair are an extremely hazardous
combination.  Most TV's have a live chassis, and voltages present can certainly
kill.

The failure could be the common DC rail, which will wipe out pic+sound.  Or it
could be an EHT fault which pulls the common rail down.  Or it could be as
simple as a dodgy power supply input component.

Clues to check for:  any "zap" sound as it collapses; any ticking sound (often
faint) once the set has shut down; any smell.

Most sets are fairly generic inside, so an experienced TV tech without a circuit
can go a long way, whereas a novice needs a schematic.

Re: Help with a fault ????


Thanks,
There is definately a clicking sound as it konks, It seems to try again a
number of times ie click. buzz, click buzz, with some white retrace lines
appearing on the screen, and the EHT collapsing each time by the looks. When
it stops ( anywhere from two to five times of this ) there is no mains hum,
EHT whine or any other sound from ther unit.
Tim
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Re: Help with a fault ????


Ticking sound is pointing to the horizontal fault.
I would suspect FBT.

Rudolf

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Re: Help with a fault ????



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Not necessarily, it can be caused by almost any overload on the SMPS
secondary making the PSU repeatedly shut down and attempt restart, a high
ESR electrolytic almost anywhere in the supply chain can screw up the
regulation with similar results.



Re: Help with a fault ????


FBT is quite common to fail in Philips.

Anyway, without having a TV on the bench one can only guess.
I already suggested to run PS on a dummy load and monitor B+.

Rudolf

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Re: Help with a fault ????



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The OP mentioned flyback lines as the set shut down or attempted to restart,
Philips have had a lot of CRT problems in recent years - gently tapping the
tube neck with a screwdriver handle might reveal the cause if this is the
case.



Re: Help with a fault ????



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I dont know much about TV's but what is that ticking sound?



Re: Help with a fault ????



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Can't hear it - can you describe it for me?  Is it a bomb?

It is the sound of the main SMPS trying to get up, then collapsing under
fault/short condition, then trying again.

Re: Help with a fault ????


Ah that explains when ATX power supplies do that, - Thanks

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Re: Help with a fault ????


The syptoms that I see certainly are consistent with the PS shutting down,
and then trying to restart.
Tim
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Re: Help with a fault ????


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Yep, take it to your local TV service tech and keep him in business.
You'll spend more time mucking around on your own than what an expert
is worth.

TV's are dangerous too, don't play with them.

Dave :)


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