Sony KV-24FV300 shuts down.

[David Farber]

This Sony KV-24FV300 powers up for about a second, then shuts down. The
front panel l.e.d. shows a blink code of two blinks. According to some
older information on the web, the two blinks indicate a B+ over current
protection. I cannot find any shorts in the set. Flyback and H.O.T. ring ok.
Does anyone know of any common faults with this set?

Thanks for your reply.

 

[David Farber]

This Sony KV-24FV300 powers up for about a second, then shuts down. The
front panel l.e.d. shows a blink code of two blinks. According to some
older information on the web, the two blinks indicate a B+ over current
protection. I cannot find any shorts in the set. Flyback and H.O.T. ring ok.
Does anyone know of any common faults with this set?

Thanks for your reply.

After further investigation, I've come up with the following observations.

With all plugs and boards attached, the set powers up and about a second
later my AC line current measurement spikes to over 2 amps and the set shuts
down.

Removal of the deflection yoke plug does not change the situation. Set still
shuts down.

With the HOT removed, and everything else plugged in, the set powers up, the
135 volt supply is normal, and it doesn't shut down. The drive signal to the
base of the removed HOT is a nice sawtooth, about 6 V p-p. The blink code
changes to four blinks which I believe means no vertical deflection.

So my question is, can a bad flyback suck a lot of current even though the
deflection yoke plug is not attached?

Thanks for your reply.

 

[Leonard Caillouet]

After further investigation, I've come up with the following observations.

With all plugs and boards attached, the set powers up and about a second
later my AC line current measurement spikes to over 2 amps and the set
shuts
down.

Removal of the deflection yoke plug does not change the situation. Set
still
shuts down.

With the HOT removed, and everything else plugged in, the set powers up,
the
135 volt supply is normal, and it doesn't shut down. The drive signal to
the
base of the removed HOT is a nice sawtooth, about 6 V p-p. The blink code
changes to four blinks which I believe means no vertical deflection.

So my question is, can a bad flyback suck a lot of current even though the
deflection yoke plug is not attached?

Why not?

Leonard

 

[David Farber]

Why not?

Leonard

With the yoke disconnected, and the HOT installed, doesn't the circuit stop
oscillating? If so, wouldn't there have to be a measurable short in the
primary windings to ground for the flyback to suck the current? Are there
further steps I can take to isolate the flyback as the problem without
actually buying a replacement? Keep in mind that the flyback does ring ok
with my Dick Smith flyback tester.

Thanks for your reply.

 

[[email protected]]

SYMPTOMS

Shutdown - 2 blinks

RESOLUTION

Found R565 10k chip resistor increased to 20k.
Does blink 2 x but only once.

HQ COMMENTS:
This resistor is part of the HV shutdown circuit. From the FBT/pin 7 to
IC561/pin 5.
If IC561/pin 5 goes above IC561/pin 6 pin 7 goes high causing Q572 to turn
on and Q006
to turn OFF. This causes IC001/pin 72 to go high turning off the Horizontal
Oscillator.


From http://fletchersite.com/

 

[Andy Cuffe]

With the yoke disconnected, and the HOT installed, doesn't the circuit stop
oscillating? If so, wouldn't there have to be a measurable short in the
primary windings to ground for the flyback to suck the current? Are there
further steps I can take to isolate the flyback as the problem without
actually buying a replacement? Keep in mind that the flyback does ring ok
with my Dick Smith flyback tester.

Thanks for your reply.

Disconnecting the yoke, or even removing the HOT, has no effect on the
horizontal oscillator. Since there is base drive, you know the
horizontal oscillator is working. B+ goes directly to the flyback, so
if there was a short to ground it would overload even with the HOT
removed. It is possible for a flyback to ring ok and still be bad.
Is there any high voltage before it shuts down?
Andy Cuffe

[email protected]

 

[David Farber]

SYMPTOMS

Shutdown - 2 blinks

RESOLUTION

Found R565 10k chip resistor increased to 20k.
Does blink 2 x but only once.

HQ COMMENTS:
This resistor is part of the HV shutdown circuit. From the FBT/pin 7 to
IC561/pin 5.
If IC561/pin 5 goes above IC561/pin 6 pin 7 goes high causing Q572 to turn
on and Q006
to turn OFF. This causes IC001/pin 72 to go high turning off the Horizontal
Oscillator.


From http://fletchersite.com/

R565 checks ok. I believe the problem is that there is too much current
being drawn in the horizontal output stage which is causing the shutdown. As
I see it, a faulty shutdown circuit would not cause the current to spike
after turn on.
Thanks for your reply.

 

[David Farber]

Disconnecting the yoke, or even removing the HOT, has no effect on the
horizontal oscillator. Since there is base drive, you know the
horizontal oscillator is working. B+ goes directly to the flyback, so
if there was a short to ground it would overload even with the HOT
removed. It is possible for a flyback to ring ok and still be bad.
Is there any high voltage before it shuts down?
Andy Cuffe

[email protected]

What I meant was there should not be any oscillation on the primary side of
the flyback with the yoke plug removed.

My latest test was inserting a 75 watt lamp in series with the 135v supply
and reinstalling the HOT. The lamp lit up very brightly and my current meter
hooked up to the 135V supply measured 630ma. There is no high voltage and no
signal at the collector of the hot.

 

[Andy Cuffe]

R565 checks ok. I believe the problem is that there is too much current
being drawn in the horizontal output stage which is causing the shutdown. As
I see it, a faulty shutdown circuit would not cause the current to spike
after turn on.
Thanks for your reply.

It's probably the flyback, or a component in the HOT's collector
circuit. It could also be an overload on one of the flyback
secondaries including the CRT itself.
Andy Cuffe

[email protected]

 

[David Farber]

Disconnecting the yoke, or even removing the HOT, has no effect on the
horizontal oscillator. Since there is base drive, you know the
horizontal oscillator is working. B+ goes directly to the flyback, so
if there was a short to ground it would overload even with the HOT
removed. It is possible for a flyback to ring ok and still be bad.
Is there any high voltage before it shuts down?
Andy Cuffe

[email protected]

What I meant was there should not be any oscillation on the primary side of
the flyback with the yoke plug removed.

My latest test was inserting a 75 watt lamp in series with the 135v supply
and reinstalling the HOT and deflection yoke plug. The lamp lit up very
brightly and my current meter hooked up to the 135V supply measured 630ma.
There is no high voltage and no signal at the collector of the hot.

 

[David Farber]

It's probably the flyback, or a component in the HOT's collector
circuit. It could also be an overload on one of the flyback
secondaries including the CRT itself.
Andy Cuffe

[email protected]

Last update. Instead of using a lamp in series with the 135 volt supply, I
hooked up my dc ammeter in series with the 135 volt supply. I also monitored
the collector of the HOT. The ammeter goes to about 1.76 amps (which seems
like a lot, and the collector waveform has the correct p-p voltage but with
lots of other oscillations that shouldn't be there. Then the set shuts off.
I'm going to order the flyback and give it a try. The high voltage is hard
to monitor because there is a delay in the reading of my meter and the set
shuts off too soon.

Thanks for your reply.

 

[Leonard Caillouet]

Last update. Instead of using a lamp in series with the 135 volt supply, I
hooked up my dc ammeter in series with the 135 volt supply. I also
monitored
the collector of the HOT. The ammeter goes to about 1.76 amps (which seems
like a lot, and the collector waveform has the correct p-p voltage but
with
lots of other oscillations that shouldn't be there. Then the set shuts
off.
I'm going to order the flyback and give it a try. The high voltage is hard
to monitor because there is a delay in the reading of my meter and the set
shuts off too soon.

You already answered my next question when you said "the collector waveform
has the correct p-p voltage but with lots of other oscillations that
shouldn't be there," which tells you that you almost certainly have a bad
flyback.

Leonard

 

[David Farber]

You already answered my next question when you said "the collector waveform
has the correct p-p voltage but with lots of other oscillations that
shouldn't be there," which tells you that you almost certainly have a bad
flyback.

Leonard

Hi Leonard,

You are most certainly correct. The new flyback fixed the set. Just for
measurement sake, the current dropped to an average of 500ma in the 135 volt
supply once the set was working.

Thanks for your reply.