Update: Pioneer PRO97

[Golf]

Yep, still kicking my but, but getting closer. I found the +9V supply
to the convergence board to be only about 4.7V. Did some resoldering
on a few plugs and got this back to normal. Prior to this it would
display misconverged colored snow. Anyway, with a color bar signal
input at the coax, I have just a black raster. I do see OSD of channel
number clearly, which is better than before the 9V problem was
corrected.
I did disconnect a diode in the powerdown Vertical def circuit
to keep set powered up for troubleshooting. It is from the Vertical
Ret (retrace?). I checked the waveform at the vertical input on the
convergence board and it is clean and good. I haven't found anything
about the vertical ret. on the schematic as far as what I should see,
to determine why this circuit is at fault. I have already replaced the
vertical/current amplifier IC, and checked many discreet components in
this circuit.
This is where I'm needing your help - I'm not familiar with
"vertical ret". What is it's function in the set? Will it prevent the
raster from displaying normal brightness? No vertical signal provides
nice bright horizontal line. Is this a clue to the fault? I've googled
and haven't found much help on "vertical ret". Thankyou for any help
here. Please keep in mind I have only been working on TV's for a few
years - no professional training obviously. Thanks again.

 

[[email protected]]

Vertical return is used because it is an actual sample of yoke current
for the feedback circuit, the same way the convergence circuit
operates. The difference is that the vertical IC usually supplies it's
own "commutated" power supply to the output stage. Sometimes that
boost pulse is used for blanking or something, but not for protection.

The RET means return. all three yokes are in series, so if any yoke
gets unplugged or open circuited for any reason, there will be no
signal on the RET. Since they are in series, any open can cause screen
burn in all three CRTs quite quickly. So using the RET to have the
signal for the shutdown circuit that all is well, they use the RET.
There will usually be a ramp or something that resembles a parabola
waveform there, and it is rectified to usually saturate a transistor
that if becomes turned of by loss of input, will either trigger a hard
blanking circuit or the shutdown.

In the RET line sense circuit, electrolytics can be critical.
Engineers deem the saturated transistor to be the best way to tell the
shutdown that all is well. This is because of a few reasons, first of
all if a connection is lost to any of the terminals of a bipolar
transistor it acts as an open circuit. Secondly, in this circuit, the
collector is not subjected to any great current or voltage, and is
very unlikely to short out, and is not connected to an inductive load
either. These factors are what made them choose the rectified base
current method for this mode of protection. It is the best, surefirest
way to assure there is vertical deflection.

There is a similar scheme for horizontal deflection, but it is not as
surefire, because the horizontal windings are in paralell, not series.
In sets with normal reactive scanning, if any yokes come disconnected
it causes a decrease in high voltage. Sets with discrete HOT and HVOT
usually have a quite sensitive circuit to detect any yoke
disconnected, but even then it does not always work. However, these
sets do not shut the HOT down when needed, only the HVOT. That's why
the owner's manual says to unplug it.

At the high side of the vertical yoke you should see something like _/
^|_/^|. that's the best I can do it in text. If you see |_ |_ |, like
a square wave, you have an open yoke circuit. Some sets depend on DC
feedback through the windings as well, so on chassis make sure you got
the same DC voltage on the vertical output as the RET. It should
always be the same. You might have to isolate your voltmeter with an R/
C filter, like a 10K resistor and a 10uF cap. It depends on your
meter.

I know I have responded on this before, but right now I don't remember
the whole thing, I'll have to go back and read it. But you asked what
you asked now, so that is the answer. The RET is used for feedback as
well as shutdown.

Now on Pioneers, sometimes the vertical circuit is on the convergence
board, which would be an STK 4274 I think. If you got one of those it
is push pull, alot more fun. It is very hard to get them anymore, but
there is a new STK that can be adapted. By shorting a couple of pins
together I think you can use an STK 391-020. However the mounting
dimensions are different. Personally if I have to do this, instead of
drilling new holes I would find some sort of clamping method, like
used in newer Mitses for example.

Actually you need a scope on the B+ line, if it does not go above
spec, jump the relay and see what you get.

Damn, I need to know if this one has seperate HOT and HVOT or uses
that funky circuit to compensate. Tell me this, where the yokes plug
in, do the foils go to the flyback at all ? (off the red wire) There
may be a seperate little transformer. We need to know this.

And last but not least, if you have a print, where the hell did you
get it ?

Weekend is coming, there will be calm times, perhaps I'll refresh my
mind with the whole situation. I know Pioneers are a pain in the ass,
but pain in the ass is my business.

JURB