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Dead Sony KV-T25SZ8 TV

S

Sylvia Else

Jan 1, 1970
0
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.
 
G

Gagi-9a6aag

Jan 1, 1970
0
Sylvia Else said:
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.


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$
 
F

Franc Zabkar

Jan 1, 1970
0
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.

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?fileid=12231

- Franc Zabkar
 
S

Sylvia Else

Jan 1, 1970
0
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?fileid=12231

- Franc Zabkar

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
 
P

Phil Allison

Jan 1, 1970
0
"Sylvia Else"


** Hey dumbass.

You misspelled "sci.electronics.repair".



.... Phil
 
C

Clifford Heath

Jan 1, 1970
0
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.

A friend and I (he very experienced) tries to fix a similar fault in a
similar Sony TV a year back. The clicking was coming from a relay in the
PSU, which appears to be driven via some circuitry from an opto-isolator
from the main board. It would appear that it would try to power up, detect
a fault, and shut off again, repeatedly. We never did get to the bottom of
it. Really, with so many rather good glass TVs on the nature strip, are you
sure it's worth the trouble?

Clifford Heath.
 
S

Sylvia Else

Jan 1, 1970
0
"Sylvia Else"


** Probably normal.

Er, yes, I meant emitter to collector.
There is an inbuilt resistor from B to E in nearly all HOTs of 20 ohms or
less.


** Bollocks.

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.
 
S

Sylvia Else

Jan 1, 1970
0
"Sylvia Else"


** Hey dumbass.

You misspelled "sci.electronics.repair".

So I did. Now why didn't the server complain?

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
Really, with so many rather good glass TVs on the nature strip, are you
sure it's worth the trouble?

Probably not, particulary as I've identified a dud transistor that is
moderately expensive to source, and whose failure may only be a symptom.
If the problem had been a failed electrolytic capacitor that I could get
from my local electronics shop, then it would have been worth having a
go at fixing it. As things stand, it's destined for the tip (or
something - see below).

But we don't get good glass TVs on the nature strip, at least not in my
suburb. The council banned getting rid of them that way (i.e. leaving
them out on an official council cleanup day), with the result that one
cannot simply go out on such a day, and pick up a TV whose only sin is
that it isn't wide-screen.

Sylvia.
 
C

Clifford Heath

Jan 1, 1970
0
Probably not, particulary as I've identified a dud transistor that is
moderately expensive to source,

I replaced the HOT in this TV also. $9 including shipping from WES.
However, HOTs are very strange devices. If you just do the basic
two-diode test, you'll probably consider that a good one has failed.
That's what I did :)... something to keep in mind.
But we don't get good glass TVs on the nature strip, at least not in my
suburb.

So drive to the next suburb. Aforementioned friend has picked up
half a dozen perfectly functional TVs that way, usually wide-screen
versions (he prefers those), and provided them to friends. Must get
a few duds, but you can drop those back.

Clifford Heath.
 
G

Gagi-9a6aag

Jan 1, 1970
0
Phil Allison said:
** Hey dumbass.

was that really nesecarry?!?!?
you really enjoy it, dont you :p

show some attitude at least toward ladies FFS :)))
 
P

Phil Allison

Jan 1, 1970
0
"Gagi-9a6aag"
"Phil Allison"
was that really nesecarry?!?!?
you really enjoy it, dont you :p
show some attitude at least toward ladies FFS :)))

** You are new here and know nothing of the past.

Sylvia is no lady.


..... Phil
 
S

Sylvia Else

Jan 1, 1970
0
Er, yes, I meant emitter to collector.


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.

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.
 
P

Phil Allison

Jan 1, 1970
0
"Clifford Heath"
However, HOTs are very strange devices. If you just do the basic
two-diode test, you'll probably consider that a good one has failed.
That's what I did :)... something to keep in mind.

** You need a " Power Transistor Tester" - published as a full construction
article in EA magazine back in May of 1988 by me. Altronics and Jaycar had
kits for it at one time.

It will reasonably accurately test the beta (or Hfe) of any power transistor
OR power Darlington pair OR horizontal deflection transistor. Very cheap
to make - uses only a few passives, a couple of red LEDs and a WW pot.

No PCB was used as it take only minutes to wire up the bits once they are
all fitted into a small jiffy box.

It will also allow close matching ( ie Vbe match) of groups of power
transistors that must operate in parallel.

Requires an external 12 volt DC source.

I would post the schem on ABSE, but like so many others I no longer have
access to the site.




..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Wild_Bull"
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).

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

Small low voltage/battery powered testers aren't very reliable, IMO, for
testing/evaluating HOTs,

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

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.

** Pure gobbledegook.

The above point being that one rarely knows for sure if they're receiving
genuine exact replacement parts nowadays,

** Instead of what - fakes ??
and testing before installation is likely the best way to find out if the
part are bogus.


** 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.

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.

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



..... Phil
 
C

Clifford Heath

Jan 1, 1970
0
** You need a " Power Transistor Tester" - published as a full construction
Thanks.

I would post the schem on ABSE, but like so many others I no longer have
access to the site.

You mean you have no access to ABSE? Spend $US3.95 at www.teranews.com and
get free lifetime access to all the binary groups, limited to 50MB/day.

Clifford Heath.
 
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