Dead Sony KV-T25SZ8 TV

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This TV died abruptly, and completely without warning, while it was
turned on. It appears completely dead, other than than that the
degaussing still works.

There was some burning smell evident immediately after it failed, but
nothing has obviously suffered heat trauma.

Presumably there's a problem with the power supply, which looks like a
switch-mode. One thing I've noticed is that when power is connected, it
emits a clicking noise - about three times a second. When the power is
disconnected, the clicking doesn't stop immediately but continues for
several seconds, slowing down.

The clicking noise isn't coming from the speakers. I assume it's coming
from a transformer or choke.

Ring any bells?

Sylvia.



Re: Dead Sony KV-T25SZ8 TV
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I'm not expert but ...

Arcing within the PSU?

Examine it really closely and if nothing is obvious it might be worth
powering up on your bench with the covers off and the lights turned way
down - but you shouldn't completely discount the possibility of internal
arcing in a cap or the transformer.

But I will bow to anyone else with experience.

Make sure you have a small, tightly focused torch, earth leakage
protection, and don't get yourself electrocuted (keep one hand in your
pocket, no loose hair, chains, cloths or anything else, don't touch etc).

If it were me I would balance the cost of a new TV - some of the flat
screens are sold at ridiculous prices v. the time, effort and cost of
repair including the possibility of spending time and effort to discover
you can't get a part  - especially if you don't already have good
connections for TV parts



Re: Dead Sony KV-T25SZ8 TV

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answer is; probably HOT
(probably BU or 2SC)

solder it out and check pins for zero ohms....it shouldnt be zero in any way
of measuring
to locate it, its right beside the HV coil on some heatsink ...beside it is
usually some elco 100 - 470uF / 160 or 250V..solder it out too and check the
cap and ESR as well....so as the diode  nearby


repair will cost you max 5$



Re: Dead Sony KV-T25SZ8 TV
On Sat, 12 Mar 2011 22:18:42 +1100, Sylvia Else

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There appears to be a short on one of the SMPS outputs.

Service Manual for Sony BG-1S Chassis:
http://www.eserviceinfo.com/download.php?fileid12%231

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

Re: Dead Sony KV-T25SZ8 TV
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Thanks for the reference.

The horizontal deflection output transistor measures 5.7 omhs from
emitter to base in either direction. It would certainly show as a short
on the SMPS output.

I can source a replacement for $15 (possibly!), but is it the cause, or
just a symptom?

Time for a new TV, I think, as suggested by by David.

Damnation - now I have to choose one - I hate doing that.

Sylvia


Re: Dead Sony KV-T25SZ8 TV

"Sylvia Else"

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** Probably normal.

There is an inbuilt resistor from B to E in nearly all HOTs of 20 ohms or
less.

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** Bollocks.


....  Phil





Re: Dead Sony KV-T25SZ8 TV
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Er, yes, I meant emitter to collector.

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Probably true, for the emitter to base.

I found what appears to be the correct schematic. The transistor's
collector emitter junction is in series with an EHT transformer primary
winding, and together they sit across the HT output from the SMPS, with
just a small inductor in the way. I must admit it doesn't look to me as
if it's performing a horizontal deflection output role - that's just how
the transistor is described in the data sheet.

Sylvia.

Re: Dead Sony KV-T25SZ8 TV
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I've bitten the bullet, and bought a new television.

Still, I'm puzzled by the failure in the old one. The transistor has
clearly failed, as far as I can see. Removing the small inductor
mentioned above stops the clicking noise, which is consistent with there
no longer being a short across the SMPS.

I'd have expected the set to now turn on and produce sound. But it doesn't.

The SMPS uses a quasi-resonant circuit, and disconnecting the inductor
has a side effect of removing the feedback for the SMPS. But on my,
admittedly limited, understanding of such circuits, it should still work.

Sylvia.

Re: Dead Sony KV-T25SZ8 TV
It's been a long time since I dealt with CRT horiz output
sections/transistors, and the latter ones were in VGA monitors.

In the Repair FAQ there are safety, testing and troubleshooting procedures
for horiz section faults, including the lightbulb in series with the HOT B+
setup, IIRC.

The HOTs (transistors) are fairly rugged semis, but operating at 15+kHZ and
high peak/fast risetime conduction cycles.

FWIW section..

A few conditions wrt HOT failures that I can recall at the moment include
bad/cold/broken solder connections, loss of horiz drive and drifting
values/faults in the tuning capacitors (the small value 1 and 2kV caps).

Small low voltage/battery powered testers aren't very reliable, IMO, for
testing/evaluating HOTs, since reliable leakage testing at higher voltages
than most small testers are capable of, should be performed to determine the
junction's performance compared to the datasheet published specs.

The above point being that one rarely knows for sure if they're receiving
genuine exact replacement parts nowadays, and testing before installation is
likely the best way to find out if the part are bogus.

My recommendations (and many other archived repair recommendations) for Sony
TVs and monitors, is to research the failure and buy all the recommended
repair parts from a Sony authorized distributor, especially for PSU and H,V
sweep faults.

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


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Re: Dead Sony KV-T25SZ8 TV

"Wild_Bull"
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** Not to forget arcing inside the CRT or the horizontal transformer.


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** 99 % of them cannot do any test on them at all.


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** Pure gobbledegook.


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**  Instead of what  -   fakes ??

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** Absolute bullshit.

No simple test will reveal a device that is merely sub-standard or of a
similar but cheaper type to the original.

The only way is to deal with reliable suppliers ONLY.


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**  Wear a belt and braces too  - do you ??



.... Phil







Re: Dead Sony KV-T25SZ8 TV
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In a vacuum?

or the horizontal transformer.

Sylvia.

Re: Dead Sony KV-T25SZ8 TV

"Stupider than Anyone Else.
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http://en.wikipedia.org/wiki/Vacuum_arc


** One of the most common causes of HOT failures.

     Dumbass.



.... Phil



Re: Dead Sony KV-T25SZ8 TV
Arcing, shorts and HV leakage can all take place within a CRT.
I've seen several CRTs that had HV leakage to the Focus element (didn't
damage the HOT though).. there may be some examples in the Repair FAQ of
this type of fault and other CRT faults.

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


We've slightly trimmed the long signature. Click to see the full one.
Re: Dead Sony KV-T25SZ8 TV


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******Bollocks.

Most horiz output internal resistors are between 25 and 50 ohms.
Besides, 20 ohms isn't 5.7ohms.  In circuit, E to B reads an ohm or
under as the secondary of the horiz driver transformer is directly
across it.. Out of circuit, a reading of 5.7 ohms E to B is a bad
transistor.  It's not common in horizontal outputs, but an E to B
short does happen.


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**** More likely a stupid answer.

 A common problem in Sonys is a bad solder connection on the secondary
of the horiz driver transformer, so instead of reading under an ohm,
the cold solder causes a reading of several ohms up to the internal
resistor value.  Simply resoldering the horiz driver will restore
proper reading if the output is otherwise OK.


Twit.

Hey, this is fun!!!!!


Re: Dead Sony KV-T25SZ8 TV

"Stroonz is a SHITHEAD  "
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** I have seen them with 20 ohms and less.

    You need to get out more.


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** The OP corrected her error in the next post  -  which like a total
shithead you have not bothered to even read.

 The 5.7 ohms was actually measured from C to B.

 And the bitch gave no clue about the use of in or out of circuit testing.



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** Not all HOT drive circuits are like that.

 Many have a low value R in series with the base with a diode across it.


** Why don't you go fuck a dead donkey ?



......  Phil








Re: Dead Sony KV-T25SZ8 TV
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Im very annoyed now, I was sipping coffee when I read that, and some
got sprayed from laughing  ;)


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Re: Dead Sony KV-T25SZ8 TV

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******* Doesn't matter if she corrected it or not.  You were INCORRECT
when you believed a 5.7 ohm E to B reading was normal in HER SONY.

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

Yes, and they were shorted.  OTOH, if you can cite a transistor that
was actually used as a horiz output that has an emitter-base resistor
of less than 20 ohms, I'll happily concede.


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******** Read above ^


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******** We don't know if she's a bitch or not.  She might be quiet
pleasant.....


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No one said all HOT drive circuits are like that.  But again, she
wasn't interested in every conceivable version of the drive circuit,
she was interested in HER Sony.  Her Sony doesn't have a "low value
resistor in series with the base". If you don't know what you're
talking about or can't offer correct specific information, you really
should pipe down, or at least qualify your opinions as just that.


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Common Phil, where does one find a dead donkey, even if one was so
inclined to be intimate with it.  You may not be the smartest guy on
the web, but you are a riot!!!

Re: Dead Sony KV-T25SZ8 TV

Oh, and the quiet above is a typo:  reverse the "e" and "t"

Re: Dead Sony KV-T25SZ8 TV
"Stroonz is a  PSYCHOTIC  SHITHEAD  "
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** I have seen them with 20 ohms and less.

    You need to get out of that asylum more.


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** The OP corrected her error in the next post  -  which like a total
shithead you have not bothered to even read.

The 5.7 ohms was actually measured from C to B.

And the mad bitch gave no clue about the use of in or out of circuit
testing.


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** Not all HOT drive circuits are like that.

 Many have a low value R in series with the base with a diode across it.

The original exchange was:

" > The horizontal deflection output transistor measures 5.7 omhs from
  >  emitter to base in either direction.

** Probably normal.  "

See -  no reference is made to any particular set in my remark .


** Why don't you go fuck two dead donkeys ?



......  Phil









Re: Dead Sony KV-T25SZ8 TV

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****** Yes, the OP did correct her error, something you refuse to
do.   You said a 5.7 ohm reading was "probably normal" for her Sony.
You were wrong and can't admit it.  Nice character flaw Phil.




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It's hard to explain this to someone who is unfamiliar with Sonys, but
I'll try again:  If everything in her Sony is normal, the E to B
resistance reading will be under an ohm in circuit.  If the secondary
of the horiz drive trans in her Sony is open or the connection is bad,
it will read the internal emitter to base resistor directly, if the
transistor is so equipped.  (some Sonys of this era use no e to be
resistor).  If the transistor is measured out of circuit, it will read
approx 35 ohms e to b if it's not shorted.  Under NO CIRCUMSTANCES
will this TV show 5.7 ohms across the e to b junction.  Such a reading
is ABNORMAL.  Perhaps you left the "ab" out of your reply.

And I know you'll requote her correcting her reading, but it doesn't
change the fact that you believed and proclaimed as fact that an E to
B reading of 5.7 ohms in HER SONY was normal.


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You know, vile, classless folk take all the fun out of a debate.

Enjoy your last word Phil......

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