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Toshiba 42H83

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Charlie East

Jan 1, 1970
0
Anyone have a Toshiba projection set sitting around with a digital converter
board they can part with? I replaced all the 10 @ 16 surface mount caps on
this one, Fixed some of the problem but not all, This set was donated to the
Church if I can get it going,
Charlie
[email protected]
 
Just how familiar are you with PTVs ?

Before you go looking for an expensive part like that you need to
verify a few things. Did you replace the STKs ? Where did you get
them ? Did you check all the return resistors ?

It helps to identify if the problem is in one of the channels
exclusively, because if it is the problem is usually in the output
circuit.

If you don't have a print, get the datasheet for the STK392-110 and
troubleshoot it like a regular OP AMP. If they use the non-inverting
input, the + and - inputs should have nearly the exact same waveform
on them. If they use the inverting input both should be a flatline at
0 volts. (the + is grounded anyway)

If you have a generator put a crosshatch on it and observe closely.
There are six channels, R, G & B, horizontal and vertical each.

Analyzing this can be tricky. For example if you have a large error in
the red horizontal, it will appear to have a red vertical error as
well, even if it does not. Taking a hypothetical case like this let's
say the red horizontal is out, on the side of the screen where is is
overstretched, it will appear to have a vertical pincusion error,
bowed out. On the side where red is compressed it will be bowed in.
This is because the pincushion is off, but that is because the beam is
not where it is supposed to be.

You'll find people quite reluctant to part with good DCMs, or
hypermodules. It is imperative to know that is the fault for sure. If
you could provide a picture of the symptom with a crosshatch patter I
might be able to analyze it. I do these things all day long. I have a
nice collection of digital convergence nightmare stories if you like.

IIRC, Tosibas blank the video when they put up the crosshairs for
adjustment, so you can't really tell if the outputs are clipping. Need
a scope for that. However, if the error is in one corner on one color,
it is likely. That generally indicates a defictive STK. Even if
they're new, I have seen them bad right out of the bag. It happens
with the 392-110s, but the 4278s are more notorious for it. They are
not shorted, but they either can't swing fully to the power supply
rails, or sometimes the slew rate is too crappy. In either case they
are not shorted nor completely open, just not good enough.

I tend to think in terms of the TV having one problem. But nowadays
you can't count on it. Some people will watch a TV until they can't
see anything. If they donated it this might well be the case. They
knew it was screwed up, and then it got screwed up worse. They suspect
the repair bill will be quite high, and they would be correct.

At any rate, make absolutely sure that the DCM is the problem, then
next time I am in the boneyard I'll see if we have a compatible one. I
don't own the shop so I dunno how much, and unfortunately it will
probably be untested.

JURB
 
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Leonard Caillouet

Jan 1, 1970
0
What is the problem? Are you are talking about the Hyper module? Did you
check the rest of the SMD caps. I have had these modules with bad caps
among the 470uF and 1uF caps. Some techs are just changing all of the
surface mount caps. I just check them and any that are suspect change them.

Leonard
 
C

Charlie East

Jan 1, 1970
0
The original problem was distorted picture,(zig-zag), I found a web site
that discribed the same problem.(techlore.com). search 42h83 . The tech said
change the [email protected] surface mount caps on the hyper module. There was also a
bulletin from Toshiba that said the same thing. After changing the caps, the
distortion cleared up.
Convergence looks good, Still picture looks good, but a moving picture had
a laging effect, kinda like ghost. The tech said I probably still had
problems on the hyper module I did check the ESR on the remaining caps on
the board, didnt find any more bad.
Charlie
 
L

Leonard Caillouet

Jan 1, 1970
0
I would change the remaining caps on the Hyper module.

Leonard
 
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