vertical ic fails over and over

[[email protected]]

Akai ct21wkd tv, lost vertical deflection an year ago for the first
time.
I've replaced the verical ic (AN5534) and the problem was fixed, but
returned after three months.
I've replaced the vertical IC again, but as it happened in the previous
time, it lasted for three more months.
The last time I've replaced all the vertical circuit capacitors (about
3) and transistors (two)
along with the vertical IC, and again, it lasted for three months.
What can it be ?
Btw, I also have white lines at the top 15% of the screen (which
appeared after the 2nd vertical ic replacement), but they don't bother
me and I'm not sure it's connected to the vertical ic failure problem.

Thanks!

 

[[email protected]]

I am sure you missed the capacitor that is causing the lines at the top
15% of the screen and causing the repeat vertical ic failures.

It is obvious you did not replace ALL the vertical circuit capacitors
if you still have the lines at the top 15% of the screen.

 

[Dave D]

Akai ct21wkd tv, lost vertical deflection an year ago for the first
time.
I've replaced the verical ic (AN5534) and the problem was fixed, but
returned after three months.
I've replaced the vertical IC again, but as it happened in the previous
time, it lasted for three more months.
The last time I've replaced all the vertical circuit capacitors (about
3) and transistors (two)
along with the vertical IC, and again, it lasted for three months.
What can it be ?
Btw, I also have white lines at the top 15% of the screen (which
appeared after the 2nd vertical ic replacement), but they don't bother
me and I'm not sure it's connected to the vertical ic failure problem.

Those lines are indicative of your problem- there is a faulty part in the
vertical section which is causing the IC to fail. My first thought is
electrolytic caps, but you say you've changed them all. Maybe one or more of
the new capacitors was faulty. I'd check every single part in the vertical
output section, check the supply rail is the correct voltage and well
smoothed.

If you get desperate and have limited test equipment- change all the parts
in the vertical output. There shouldn't be many, none of them will be
expensive and it'll be a lot cheaper than keep buying output ICs! There
could be a marginal part which is failing under stress which you might never
find with normal testing procedures.

Don't forget to reflow all the solder joints in the vertical section as a
matter of course, and while you're at it do the same to the power supply.
Check any components on the yoke are OK and the correct value.

Incidentally, has the vertical output gone altogether, ie seriously squashed
picture or horizontal line? If not, and the only symptoms are white lines in
the top of the picture then chances are the IC is fine, some passive
component is causing the problem. Again- capacitors are the likely culprit.
Forget that you already changed them, electrolytics are notoriously
unreliable and could easily have failed again.

Dave

 

[Robby]

I am sure you missed the capacitor that is causing the lines at the top
15% of the screen and causing the repeat vertical ic failures.

It is obvious you did not replace ALL the vertical circuit capacitors
if you still have the lines at the top 15% of the screen.

Also, in addition to the other tips you have been given, if it doesn't
have one, add a heat sink to the IC. Are the replacement IC's the same package
material as the original? For example, some original IC's may be ceramic while
the replacement may be plastic. There are obvious heat transfer property
differences between the packages. Don't forget to use heat transfer compound
between the heat sink and IC. Just my 2¢.

 

[[email protected]]

Thank you all, you were all right. It seems I forgot a capacitor (or
two).
Since I don't have the schematics and couldn't figure exactly where the
vertical circuit starts and where it ends,
I've tried to replace some more capacitors in the nearby (along with
the vertical IC again) by following the connections on the board, and
it seems I got it right. The tv works, but more important - the top
white lines are gone, so I hope
this time the IC won't burn so quickly.

Thanks again.

 

[Mark]

glue a heat sink onto it for good measure.
Mark

 

[Sam Goldwasser]

glue a heat sink onto it for good measure.
Mark

What model? There are some TVs (there was at least one Philips model) that require
some circuit modifications to prevent this.

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