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Sony TV, collapsed field
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Grumps
electronics forum beginner


Joined: 14 Jun 2006
Posts: 31

PostPosted: Wed Jul 19, 2006 10:05 pm    Post subject: Sony TV, collapsed field Reply with quote

Sony KVX2142, ae-1c chassis. Picture is severely squashed vertically, with
bright band in the centre. Preliminary investigation suggests that the HT is
ok (I get a picture), and the horizontal drive is also ok. The 27V for the
vertical deflection circuitry sits as 12V; there must be some path from the
12V to the 27V.
According to the circuits, the FBT generates the 27V supply via a resistor
(0R47), diode, and a elec cap. There would appear to be no volts either end
of the res. This would seem to indicate the FBT is kapput, but only the
secondary that is used for the 27V bit. Is this possible/likely?
Before I splash out 50+ for a replacement, I'm wondering if I could make a
separate 27V supply.
Comments? Ta
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James Sweet
electronics forum Guru


Joined: 01 May 2005
Posts: 1386

PostPosted: Wed Jul 19, 2006 10:45 pm    Post subject: Re: Sony TV, collapsed field Reply with quote

Grumps wrote:
Quote:
Sony KVX2142, ae-1c chassis. Picture is severely squashed vertically, with
bright band in the centre. Preliminary investigation suggests that the HT is
ok (I get a picture), and the horizontal drive is also ok. The 27V for the
vertical deflection circuitry sits as 12V; there must be some path from the
12V to the 27V.
According to the circuits, the FBT generates the 27V supply via a resistor
(0R47), diode, and a elec cap. There would appear to be no volts either end
of the res. This would seem to indicate the FBT is kapput, but only the
secondary that is used for the 27V bit. Is this possible/likely?
Before I splash out 50+ for a replacement, I'm wondering if I could make a
separate 27V supply.
Comments? Ta




Very unlikely to be a bad flyback, sounds like something is shorted in
the vertical deflection circuit and pulling the supply down.
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Grumps
electronics forum beginner


Joined: 14 Jun 2006
Posts: 31

PostPosted: Thu Jul 20, 2006 6:33 am    Post subject: Re: Sony TV, collapsed field Reply with quote

James Sweet wrote:
Quote:
Grumps wrote:
Sony KVX2142, ae-1c chassis. Picture is severely squashed
vertically, with bright band in the centre. Preliminary
investigation suggests that the HT is ok (I get a picture), and the
horizontal drive is also ok. The 27V for the vertical deflection
circuitry sits as 12V; there must be some path from the 12V to the
27V. According to the circuits, the FBT generates the 27V supply via a
resistor (0R47), diode, and a elec cap. There would appear to be no
volts either end of the res. This would seem to indicate the FBT is
kapput, but only the secondary that is used for the 27V bit. Is this
possible/likely? Before I splash out 50+ for a replacement, I'm
wondering if I
could make a separate 27V supply.
Comments? Ta




Very unlikely to be a bad flyback, sounds like something is shorted in
the vertical deflection circuit and pulling the supply down.

Thanks.
I thought that too. But why can I see 12V on the 27V supply, but nothing on
the anode side of the diode from the FBT? But then, I can't find the path
(from the circuits) from 12V to 27V either!
The power supply circuit for this 27V seems quite simple; winding on FBT,
0R47 resistor, diode, and 680u cap. I can't see anything (Tek scope, not
multimeter) on the winding, res, or diode anode. Only see 12V when you get
to the other side of the diode.
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Grumps
electronics forum beginner


Joined: 14 Jun 2006
Posts: 31

PostPosted: Thu Jul 20, 2006 7:57 am    Post subject: Re: Sony TV, collapsed field Reply with quote

James Sweet wrote:
Quote:
Grumps wrote:
Sony KVX2142, ae-1c chassis. Picture is severely squashed
vertically, with bright band in the centre. Preliminary
investigation suggests that the HT is ok (I get a picture), and the
horizontal drive is also ok. The 27V for the vertical deflection
circuitry sits as 12V; there must be some path from the 12V to the
27V. According to the circuits, the FBT generates the 27V supply via a
resistor (0R47), diode, and a elec cap. There would appear to be no
volts either end of the res. This would seem to indicate the FBT is
kapput, but only the secondary that is used for the 27V bit. Is this
possible/likely? Before I splash out 50+ for a replacement, I'm
wondering if I
could make a separate 27V supply.
Comments? Ta




Very unlikely to be a bad flyback, sounds like something is shorted in
the vertical deflection circuit and pulling the supply down.

My mistake. I had not looked under the circuit board, so just assumed which
was the FBT feed to the resistor. I got the wrong end! The 0R47 is open. Q
is, why did it blow?!
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Grumps
electronics forum beginner


Joined: 14 Jun 2006
Posts: 31

PostPosted: Thu Jul 20, 2006 9:34 am    Post subject: Re: Sony TV, collapsed field Reply with quote

James Sweet wrote:
Quote:
Grumps wrote:
Sony KVX2142, ae-1c chassis. Picture is severely squashed
vertically, with bright band in the centre. Preliminary
investigation suggests that the HT is ok (I get a picture), and the
horizontal drive is also ok. The 27V for the vertical deflection
circuitry sits as 12V; there must be some path from the 12V to the
27V. According to the circuits, the FBT generates the 27V supply via a
resistor (0R47), diode, and a elec cap. There would appear to be no
volts either end of the res. This would seem to indicate the FBT is
kapput, but only the secondary that is used for the 27V bit. Is this
possible/likely? Before I splash out 50+ for a replacement, I'm
wondering if I
could make a separate 27V supply.
Comments? Ta




Very unlikely to be a bad flyback, sounds like something is shorted in
the vertical deflection circuit and pulling the supply down.

Replaced 0R47 res after I decided to measure the voltage on the res
properly, doh!
TV now works Smile
I wonder why it broke. Could it be linked to our new policy of switching off
at the mains and not leaving it in standby?
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Leonard Caillouet
electronics forum Guru


Joined: 24 Mar 2005
Posts: 400

PostPosted: Thu Jul 20, 2006 12:19 pm    Post subject: Re: Sony TV, collapsed field Reply with quote

"Grumps" <grumpsnothere@hotmail.com> wrote in message
news:4i914bF2nof1U1@individual.net...

Quote:
Replaced 0R47 res after I decided to measure the voltage on the res
properly, doh!
TV now works Smile
I wonder why it broke. Could it be linked to our new policy of switching
off at the mains and not leaving it in standby?

I see Sony sets with only a resistor in the supply from the FBT secondary
open often enough with no other issues to not worry about it any more. I
think the resistor is just sized conservatively. I doubt that it has
anything to do with your power configuration. We do see a lot of bad solder
joints on the vertical outputs and that could play a role. Like the HDT, we
always resolder the vertical output when we service a Sony.

Leonard
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Grumps
electronics forum beginner


Joined: 14 Jun 2006
Posts: 31

PostPosted: Thu Jul 20, 2006 12:52 pm    Post subject: Re: Sony TV, collapsed field Reply with quote

Leonard Caillouet wrote:
Quote:
"Grumps" <grumpsnothere@hotmail.com> wrote in message
news:4i914bF2nof1U1@individual.net...

Replaced 0R47 res after I decided to measure the voltage on the res
properly, doh!
TV now works Smile
I wonder why it broke. Could it be linked to our new policy of
switching off at the mains and not leaving it in standby?

I see Sony sets with only a resistor in the supply from the FBT
secondary open often enough with no other issues to not worry about
it any more. I think the resistor is just sized conservatively. I
doubt that it has anything to do with your power configuration. We
do see a lot of bad solder joints on the vertical outputs and that
could play a role. Like the HDT, we always resolder the vertical
output when we service a Sony.

Thanks. I'll rest assured.
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