Philips oldtimer: 20 year old tv set died

[Andy]

My old (20 years) faithful Philips TV-set died last day, and I have tried to
find the cause, without success. As far as I know, I think it is in the
startup circuits.

What do I know?

-Chassis: 26CS5779/13Z
-Death: Just died while watching
-Fuses: checked OK

Symptoms:

-No high tension.
-Faint hiss in speaker
-Responds to remote control but channel indicator dead.
-13V and 190V test points on board have no voltage.
-140V collector-emitter voltage on flyback transistor. No base voltage.
Unsoldered and checked OK.
-Most transistors tested by using diode test. 0.7v drop. =ok
-Diodes checked OK.

Any clues as where to look?
thanks a bunch!

Andy

 

[Jerry G.]

If you put a scope on the base of the HOT, do you get the startup pulse
train? If so, this means that the kick start for the scans and power supply
should normally be okay.

There is a chance that there is a scan or HV fault, and it is going in to
the protect mode. In many sets, when they do this type of fault, I have
found them to have defective capacitors, and or a defective flyback
transformer. It is also possible at the same time to have some other failed
components as well.

--

Jerry G.
=====

My old (20 years) faithful Philips TV-set died last day, and I have tried to
find the cause, without success. As far as I know, I think it is in the
startup circuits.

What do I know?

-Chassis: 26CS5779/13Z
-Death: Just died while watching
-Fuses: checked OK

Symptoms:

-No high tension.
-Faint hiss in speaker
-Responds to remote control but channel indicator dead.
-13V and 190V test points on board have no voltage.
-140V collector-emitter voltage on flyback transistor. No base voltage.
Unsoldered and checked OK.
-Most transistors tested by using diode test. 0.7v drop. =ok
-Diodes checked OK.

Any clues as where to look?
thanks a bunch!

Andy

 

[Andy]

Thank you for your time, Jerry.

I will hook up the scope tomorrow and let you know the result.

Andy

 

[[email protected]]

I repaired a Philips set like that last year (K40 chassis) with those
symptoms. It was dry joints near the line transformer - given the age
of the set and the heat generated in use and hence heating- cooling
cyles, that was not a surprise! My tip? resolder EVERYWHERE before
undertaking expensive component swapping.

If not, ....Could be an open resistor in the deflection area.
check the modules on the chassis, remove and reinsert them.

In another K40 set I worked on, There was a red or brown wire from the
power supply to a module on the mainboard which had broken internally -
set was stuck in standby with hiss. I suggest you check all cables like
that with a multimeter

good luck, Ben

 

[[email protected]]

My old (20 years) faithful Philips TV-set died last day, and I have tried to
find the cause, without success. As far as I know, I think it is in the
startup circuits.
What do I know?
-Chassis: 26CS5779/13Z
-Death: Just died while watching
-Fuses: checked OK
Symptoms:
-No high tension.
-Faint hiss in speaker
-Responds to remote control but channel indicator dead.
-13V and 190V test points on board have no voltage.
-140V collector-emitter voltage on flyback transistor. No base voltage.
Unsoldered and checked OK.
-Most transistors tested by using diode test. 0.7v drop. =ok
-Diodes checked OK.

Apart from broken solder connections on the deflection board and power
supply (which should be fixed, regardless of the symptoms), your TDA3576
line oscillator may have died.

 

[Andy]

Now, I have hooked up the scope to the base of the scope and found no pulse
train on startup exept one transient burst that seems like startup noise.
However, on shutdown there is a square wave for a fraction of a second. This
is accompanied with a sharp "click" in the speaker and discharge "tweet"
from the power supply area. To be more precise, that "tweet" is actually a
frequency sweep starting at around 1 kHz and increasing.

Martin Bakker suggested that it could be the TDA3576 that has broken. I will
start searching for a datasheet for that device. Or does anybody know on
which pin the output is?

Thanks a lot for your help!

Andy

 

[Andy]

Sorry, got Maarten's name wrong. My apologies!