"Jason D." wrote in message
...
On Sat, 22 Oct 2005 08:34:55 -0400, "Leonard Caillouet"
wrote:

and ESPECIALLY that samsung is using these ICs in place of convergence
rings. Oh boy. Many samsung models didn't come with these rings on
the yokes. By the way, the convergence windings is about 20 turns on
each one of four sectors on the ferrite ring. Very, very low ohms for
the poor IC to drive them.

Cheers, Wizard

What do you mean by "ICs in place of convergence rings?"

Well, with active convergence disabled, the convergence rings that you
get green CRT centered then move other two CRTs convergenced to that
green in the center (usually!) or other models had red and blue set
certain distrance from green and finish rest of way with convergence.

Now, many Samsung units did not use the rings. Relying on ICs to push
all the beams together is very hard job for both STK ICs, hence runs
much harder and very hot. That's the reason for fairly high failure
rates.

Think of a thick wall tube about 1/2" length, that's the ferrite core,
four windings in one layer in four sectors, each sector 20 turns
around the core (toroidal). The assembly goes through the CRT's neck.
Others like RCA uses 4 poles with more turns around each pole and
easier to pull beam around and less stress on the convergence amps.
Oh yeah, Samsung sometimes used sloppy solder joints (just magnet wire
and wirings twisted together & soldered. I had one come apart once.

I have yet to see convergence of this Thomson (RCA) discrete
convergence amp design fail YET except for rare thermal defective,
only happened once and was fixed by co-worker 2 years ago.

Cheers, Wizard

The inductance on the Samsung convergence yokes are not much different
than
other brands. They tend to run a little hotter than some that use the
same
chips, but virtually every manufacturer that uses these outputs has
similar
reliability. Some use more or less resistive loading on the outputs, but
they all run pretty hot.

Leonard

I have never noticed that they did not have centering magnets. Every one
that I have done was pretty close after repairing the output module. In
other words if the variance in the yokes is very large, they have to correct
the excessive offset with dc bias? Not a good design, IMO. This would make
them run hot. The last one that I measured ran at about 60 degrees C,IIRC,
pretty typical for the STK392-040. That is with the back off. They likely
run hotter with the back on, due to the fact that they are mounted so high
in the set compared to other brands. Also a dumb design, IMO. Never saw
one where excessive bias was the case, as one thing we always check is for
dc ofset of more than a couple hundred millivolts on the outputs ( a habit
developed in the old Novabeam days...). But then, I have only done a few of
this set and they were pretty routine, except that tweaking the convergence
is a PITA and the various adjustments seem to interact a lot.

Leonard