"T o d d P a t t i s t" bravely wrote to "All" (11 Oct 05 11:34:16)
--- on the heady topic of "LA7838 Vertical IC and Mitsubishi CS-3535R"


That kink might be due to ripple in the vertical IC's supply voltage.
Follow the vertical IC's supply lines until you get to the filter
electro and rectifiers from the flyback derived +24 volts, change
these too.

A*s*i*m*o*v


Todd From: T o d d P a t t i s t
Todd Xref: core-easynews sci.electronics.repair:344895

Todd I'm at the end of a long repair of this Mitsubishi CS-3535R.
Todd I've replaced the switching regulator and related caps to
Todd get the primary side working, the 30 volt regulator
Todd transistor and related zener with bias resistors that burned
Todd up, a burned zener and bad cap near the "black level
Todd corrector IC," a couple of fuses and finally the vertical
Todd output IC - a Sanyo LA-7838 and all the caps in the vertical
Todd section.

Todd The initial failure involved smoke and the repair was a
Todd pain, as I smoked several components on the main board and
Todd saw smoke once in the vicinity of the CRT neck. The last
Todd bit of repair was the replacement of the LA-7838, which I
Todd replaced with an NTE sub.

Todd The picture currently has a slightly brighter horizontal bar
Todd about 20% down from the top. The scan lines are slightly
Todd closer together there, and I suspect that it is the closer
Todd scan lines that make it appear brighter there, but it may
Todd actually be brighter. The picture is slightly compressed at
Todd the line, but looks OK above and below. The caps were all
Todd replaced in the vertical section hoping to get rid of the
Todd vertical problem (which was not there prior to the power
Todd supply problems.)

Todd I've gotten advice from some here whose advice I really
Todd respect, and the consensus is that it's probably not the
Todd vertical IC, despite the fact that I used a sub. However,
Todd having replaced all the electrolytic caps in the vertical
Todd section, I'm not sure where to go now.
[,,,]

.... 'Keep the smoke inside.' -- 1st Rule of Electronics.

Since the B+ for vertical deflection circuitry flyback derived and is
powered by the flyback it won't have the normal "drift over the
vertical scan" like in the power line derived B+... ...by the way, 100
mv ripple is terrific, only about 1%, so I don't think that is an
issue.... if you think it is, tag on an additional filter cap after the
series diode coming from the flyback.... say 470uf at 35 volts.... see
if that makes a change for the better.
Are you certain that the yoke is not defective.... did it ring test OK?
The LA7838 or NTE subs are fairly cheap, go ahead and replace so you
can confirm that the problem is not with the chip.... the NTE subs for
the Vert Delf chips have always works fine for me. The small cost for
the chip is a lot cheaper than many hours pulling out your hair.
Look for leaky diodes other than the zeners.
It is possible that one of the new replacement caps has marginal ESR...
I always check two or three of them in a package and select the very
best one for critical circuits. Not all new parts are always good.
electricitym
..
..