Riddled TV Repair Forum

Jerry · Guest

*** Hi Guys,

I just keep plugging away at my big old Sony. Latest: I replaced both STK's
with a pair of cheap Korean ones. This time I socketed them with Augat prototype
pins as per my earlier post. Came out really neat. Having the sockets let me
ohm out the all the STK connections, verifying that every pin was connected to
what it was supposed to be connected to - and that it was NOT connected to anything
it was NOT supposed to be connected to - like say, the adjacent pin :). This
was necessary because the cheap single-layer phenolic PC board had started
to suffer from raising lands - and had blossomed into little green wires.
In fact, I did find one miswire - mea culpa.

Turned the TV on - flawless picture. Whew! How long will it last?
Turned out, it lasted about two days. The current pattern seems to be as
follows:

1. You can turn the TV on and watch it as long as you like.
2. If you turn the TV off and then turn it back on quickly, it might come
up with no vertical sweep - just a set of three RGB wiggly lines going
across the middle of the screen.
3. If you then turn it off and on again, you get a full raster - but not
converged. And the -15V fuse on the convergence board is popped. I
believe that when the set comes up with no vertical sweep, the STK's draw
excessive current because the vertical deflection coils then look like
short circuits.
4. Install a new -15V fuse and GOTO 1.

So now I need to figure out why the vertical sweep is going away. For all
three colors. It's an interesting system; there are actually two sets of
vertical output buffers, feeding two sets of horizontal yoke coils.
One is the STK's, which only output minor correction signals. The other is
a set of uPC1498H chips, which miraculously produce a 60V p-p output from
external power of +/- 15V! Built-in charge pumps, I guess.

I don't think that anything is overheating - my three Dell case fans
are keeping the whole convergence board nice & cool. Hopefully, the problem
is on the convergence board - which is nice & easy to get to - and not the
A board, which is buried in the back of the set.

- Jerry

Google

Terry · Guest

I'm not saying that the I/C's are bad again, but those cheap China made ones
are crappy to start with. I will not take the effort to use them in any set,
because I've wasted many hours and money on that junk. Sanyo or NTE's are
what I always use with no after replacement problems. Enough said. Enjoy
your day.

Terry

Harry · Guest

Those knock offs can come back and bite you. You should use the OEM on this set or any set. You may end up with more damage then expected if these
cheapies fail.

Harry