I don't think you should question your ability at this point. If I've
read your decription correctly, this is an interesting one.
Forget the pin ckt with this symptomology. From your quite apt
description I think it is a sync problem. The color problems are due to
loss of burst timing and the bars are due to loss of pedestal for DC
restoration.
The interesting part here is that apparently V sweep is polluting the H
sync. There are not that many places in the set this could happen. One
BIG possiblity is grounds. Another is filtering on the vertical supply
line, but I would guess you've already been there.
I know that many otherwise competent techs hardly ever touch a scope,
but I don't think you're getting out of this without one. It took us
years to get used to the 169, and it'll still throw us a curve now and
then. Due to the design, symptom analysis can decieve sometimes. For
example, the famous .056/400V that opens, by all normal logic should
cause a narrow raster, but due to the specific design of the 169 the
opposite occurs.
Have a look at the funky vertical circuit, and I mean HAVE A LOOK,
because that is one place where H and V meet. They use an H pulse to
reset the SCR which is the V output. With your symptom I would
definitely scrutinize that circuit, especially since it is so reliable.
I have been around for the entire life cycle (thus far) of the 169 and
the only V sweep failures I've ever had included a bad connection to
the yoke wire, and the V kill transistor, with the sole function of
killing V sweep during degaussing. Neither failure was related to any
components in the V sweep ckt.
There is something wrong with the inputs to the sync ckt, whether it is
the video coming in, or the feedback.
Unfortunately without in depth study of the original training manual,
and precise data on the jungle IC, part of this is guesswork at best.
All we can do is try to make good guesses.
Yep, you got a fun one there. One thing I would do as a test, although
I haven't thought out just how to implement it as of yet, would be to
try different levels of video input. Of course it's a simple matter to
cut the level with resistors, but I would be very intersted in seeing
what happens if you increase the input level to say 2 V P-P. If the
behaviour of the sync ckt changes, especially if it straightens out,
you are overriding some type of pollution at the input to the sync. If
the abberration stays the same I would say it is related to the sample
from the flyback, fed to a pin of the jungle for reference. I would not
take this to the bank just yet, it is a guess; but I think you will
find it to be the latter, that is the feedback. It is only a guess, but
it's based on 30 years experience.
At this point I like cheap and dirty solutions too, so I got
repairworld. You get about 500 symcures on a 169, but by filtering with
search criteria, I only got one that matches what you describe. CR4712
which should be an 8.2 V Zener. As nice as it is to run down a really
wierd problem with possible kudos from people here, if it is CR4712,
throw it in and call it a day. I love getting highly technical, showing
my ass so to speak, but to make money things need to get the F___ out
the door. If it is indeed CR4712, lemme know, I will be interested in
at least taking a look at the schematic and figuring out HOW this
causes that, but it is better to get the job done and then figure it
out academically (or would that be postumasley ?
)
Here's where it gets wierd (this IS a 169). You might want to run an S
video input to it. If your particular version has a digital COMB
filter, the problem might lie therein. I would be surprised to see a
perfect picture on S video, but it could happen. I know that F___ing
beast and you might find that the video is indeed distorted, but
because of improper inputs to said COMB filter. Sometimes things are
interdependent on each other, which, especially in a 169, can lead you
down the garden path.
We will tame this beast, but let me give you an example of how it can
be ;
Every once in a while this direct view 169 would come on with no audio
and the menus shifted, IIRC to the left. IIRC the usual problem is that
they're shifted to the right. Everybody in the county I think worked on
it, turned out to be the 503Khz crystal off the jungle IC. Why ?
This was one of those sets...."this is your job muth______". It was
very important and they gave me all day at $23 an hour which is rare. I
had to do it. How did that part cause that symptom ?
Oh, originally it came in for a blown HOT, but the .056/400V was fine,
geometry was fine, except once in a while this symptom would occur.
If you study the print of the 169 you will see that the EPROM is not
initialized when you plug it in, that doesn't happen until power on.
The 503K rock drives the countdown chain, which is needed for H sweep.
The EPROM runs off of H sweep. What was happening is that sometimes the
oscillator didn't start immediately, and the data from the EPROM to the
micro came too late. A 169 will run without an EPROM, but it's in some
type of "fallback" mode or something.
The original HOT failure probably happened when the divider clock drive
stopped with the HOT in the on state, which interestingly did not
recur. The reason for no audio was that the set didn't know which one
of the about 50 different audio circuits it had.
That's how they are, and in this business, it is not even the
beginning. A co-worker named Art once quipped "It's getting to where a
bad speaker can cause no hi voltage", and Sony, I guess not make a liar
out of the guy made it so. I am serious.
You think you got it bad ? (well you do on this one somewhat) I have
had to adjust vertical height to fix a greyscale proplem. That was a
Sony, at least you don't have one of those.
Anyway good luck, and let us know what you find. If you got the print,
there is a section outlining whaich versions have which features. If
that chart indicates that it has a digital COMB filter (likely) do use
an S video input to at least confirm that the problem is not there. Of
course if it is OK with S video then the problem is there.
Also, if you want to rule out pin problems, reduce the constrast level
and turn up the G2 to where you have retrace lines. I bet you'll find
that the raster IS actually there, just blanked.
Best I can do for now, throw us more info when you got it and we'll go
from there.
JURB
