I meet a client who wanted her TV checked by
a technician and after asking her a few questions about the nature of the
problem, I realized I was not getting the real picture of how the screen was
since she was talking of picture being washed being out.
So I requested her to send me the screen shot
of the TV screen via whatsup and this is what I got.
After getting the screen shot I now realized
the TV actually has a problem and need to be checked.
In the beginning I thought maybe it was just
a setting problem which I could have handed remotely.
So I passed by and picked it up, back to my
workshop I opened the TV and I headed straight to the RGB circuit.
I decided to attack this problem by talking
the voltage reading on this circuit and here I what I got and wrote I down on a
piece of paper.
With the data collected now it is time to
analyse it, in politics they say numbers don’t lie, this also hold true in
electronics and therefore let us analyse each line at a time.
9Volt line reads 8.98 volts which is within
the range, RGB bias 1.6 volts is within the range also.
Come to the RGB Amplifier voltage is 122Volts
and here I have problem with this voltage since on the PCB board it was marked
as 180Volts and therefore I will need to do more testing on this line.
Usually a drop in voltage on an outlet maybe
caused by faulty capacitors and now it is time to pull out my ESR meter to test
the capacitors on this line and luckily they are very few.
I started with the capacitor C540 rated
4.7uF/250V near the fly-back transformer and this is what I got.
A capacitor rated 4.7uf/250V should not have
ESR reading of more than 10 ohms but here it is reading 0.15K ohms!
A little mathematics we get 0.15 K X 1000=
150 ohms, this is far too high ESR which is capable of bringing down even fighter
jet without a single shot.
Also note that the Capacitance was 4.7uF but
now it is reading 909.9 nF or 0.9 uF!
I replaced this capacitor with another of the
same value and voltage which I found on a junk nearby and after testing it with
my ESR meter and found it health I did the replacement.
I assembled the board hurriedly since I was
sure I got the culprit and also time is a limited resource (we have only 24
hours a day, take away eight hours sleeping)
I applied the power and to my surprise the
problem was still there but now the screen is not white but had some color as
you below.
I Continued checking for any related
component on that line and I was almost giving up when I noted a capacitor on
the neck of CRT neck board which was also rated 4.7uF/250V and testing it I
noted the ESR was also very high and by the time I removed it from the board
one leg was already rotten and broke out, The capacitor was labelled C901 (4.7uF/250V)
I also replaced this capacitor and after
applying the power with my eyes fixed on the screen I was happy with the
results.
Kindly noted that the two capacitor has no
sign of stress or top swollen and therefore a tech without an ESR meter will
not have it ‘as business as usually’ and he or she might even fail to do this
simple repair.
Thank you friends
Stay safe
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