Sony KV27EXR20 comes on with sound 10 to 20 minutes before picture

[Barry Minchey]

Subject pretty well describes the problem. When I turn the set on, I
get the degauss sound then sound from the selected channel. It takes
10 to 20 minutes before the picture will come on. For a long time, I
just left the set on 24/7. What components could be responsible here?
I have schematics, soldering iron and have repaired this TV a few
times in the past. Would like to revive it one more time. Your help is
appreciated!!!

Thanks!

Barry

 

[David]

Subject pretty well describes the problem. When I turn the
set on, I
get the degauss sound then sound from the selected
channel. It takes
10 to 20 minutes before the picture will come on. For a
long time, I
just left the set on 24/7. What components could be
responsible here?
I have schematics, soldering iron and have repaired this
TV a few
times in the past. Would like to revive it one more time.
Your help is
appreciated!!!

Thanks!

Barry

The CRT is failing. The AKB circuit blanks the screen if the
emission is below a certain point. You may be able to get a
little more life out of it by increasing the G2 voltage a
bit.

David

 

[Barry Minchey]

Thanks David! Is that an adjustment on the flyback?

 

[David]

Thanks David! Is that an adjustment on the flyback?

Usually, yes (the lower one). Some Sony sets had the G2
adjustment on the CRT socket board. I do not recall which
one was on this model.

David

 

[James Sweet]

The CRT is failing. The AKB circuit blanks the screen if the emission is
below a certain point. You may be able to get a little more life out of it
by increasing the G2 voltage a bit.

David

That's certainly possible, but before condemning the CRT it's worth making
sure that's the problem. When I've seen this happen, the picture will flash
for a while and then finally come on, if it didn't do the flashing thing,
suspect something else.

 

[Barry Minchey]

It does flash on and off before it finally comes on. What have you
found when you had that problem?

 

[James Sweet]

It does flash on and off before it finally comes on. What have you
found when you had that problem?

Just what the other guy said, weak CRT causing the AKB circuit to blank the
picture.

 

[Barry Minchey]

I found the G2 on the board attached to the CRT. When I dial it up the
flickering begins sooner than before. It certainly isn't acceptable. I
saw a post from 1999 from a David which may have been you.

"Here is a bit of information regarding the video blanking at turn on
in Sony tv
sets that use the IK detect line.

With the tv set in a full cold start, look at the cathodes of all
three of the
guns with the oscilloscope. It will take some work with the scope
settings to see
the blanking pulses during the vertical retrace time.

Take a good look at the pulses, they all 3 should be fairly close to
the same P-P
value, usually between 50 and 150 volts. If one of them is much
smaller or much
larger than the other 2 the crt guns are getting very weak and way out
of balance
causing the blanking problem at turn on. At this point the only
proper fix is to
replace the picture tube.

In about 50% of the cases a newer low current crt rejuve only on the
bad gun can
sometimes rebalance the guns for better AKB performance.
In some other cases a slight increase in the g2 voltage will allow a
better turn
on and gray scale.

We have seen a lot of older Sony tv sets coming in with the same
symptom as he
described it with the above troubleshooting and failure result.

Some older sets also had bad solder connections to all of the voltage
regulators
in the center of the main circuit board.

The ones with the stand up power supply on the side of the chassis
have a special
capacitor 1000uf16v that goes bad and can cause poor power supply
regulation.

David".

I hate to toss out what was a very nice set. Do you have any thought
that the power supply board could be at fault? I could certainly
replace the capacitor mentioned above if it would do any good. I
apologize, I'm still in denial.

Barry

 

[James Sweet]

I hate to toss out what was a very nice set. Do you have any thought
that the power supply board could be at fault? I could certainly
replace the capacitor mentioned above if it would do any good. I
apologize, I'm still in denial.

Barry

You could measure the output of the power supply, but the tube is almost
certainly shot. Perhaps you could find a lightning damaged or otherwise
defective set with a good tube? If you're in the Seattle area I have a dead
27" Sony console with a good tube you can have but shipping is not
practical.

 

[b]

Subject pretty well describes the problem. When I turn the set on, I
get the degauss sound then sound from the selected channel. It takes
10 to 20 minutes before the picture will come on. For a long time, I
just left the set on 24/7. What components could be responsible here?
I have schematics, soldering iron and have repaired this TV a few
times in the past. Would like to revive it one more time. Your help is
appreciated!!!

Thanks!

Barry

how old it this tv?
-B

 

[Jerry G.]

From our experience, most of the time this is caused by the CRT going
weak. It is possible to have a power supply fault that can cause this
type of symptom, but that is very rare. When the CRT is very week, the
AKG circuits keep it biased off. In the case that the CRT is taking
very long to warm up to have enough emission, the AKG circuits will
keep it biased off until the emission is high enough.

At this point, I would be looking for a new TV set.


Jerry G.
======

 

[David]

I found the G2 on the board attached to the CRT. When I
dial it up the
flickering begins sooner than before. It certainly isn't
acceptable. I
saw a post from 1999 from a David which may have been you.

"Here is a bit of information regarding the video blanking
at turn on
in Sony tv
sets that use the IK detect line.

I hate to toss out what was a very nice set. Do you have
any thought
that the power supply board could be at fault? I could
certainly
replace the capacitor mentioned above if it would do any
good. I
apologize, I'm still in denial.

Barry

Hello Berry,

I did not write the archived post, but it appears largely
accurate.

I assume you do not have a schematic of this set, but there
is one more thing you can try. You may have low heater
voltage on the CRT, but first you have to determine how the
CRT filament voltage is supplied. A simple voltmeter can not
be used to measure the filament voltage. These sets get that
voltage from a winding on the horizontal output transformer.
There are two cases: 1) the winding directly feeds the high
frequency AC to the filament [usually through a low
resistance voltage dropping resistor of 2 - 5 ohms], or 2)
the voltage is rectified and filtered with a capacitor and
DC is fed to the filament [again possibly through a dropping
resistor]. If yours is AC fed, Bridge the dropping resistor
with one of equal value and see if that helps. If so, you
can leave the resistor bridged and coax a bit more life out
of the set. If it is DC fed, check the filter capacitor for
high ESR or just replace it. If that helps your are done, if
not, try bridging the dropping resistor as above.

David

 

[Barry Minchey]

Thanks all!!!! I'm convinced.

weak. It is possible to have a power supply fault that can cause this
type of symptom, but that is very rare. When the CRT is very week, the
AKG circuits keep it biased off. In the case that the CRT is taking
very long to warm up to have enough emission, the AKG circuits will
keep it biased off until the emission is high enough.

At this point, I would be looking for a new TV set.


Jerry G.
======