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Odd D9200 behavior
lilshawn:
well, i dug out the old scope and checked the hsync going into the IC and it's rock solid. so the sync going in is not the problem.
next i'll have the check the H-out from the chip and see what it looks like. if it's good, it's further down the chan in the actual drive section... but if the output is dirty, it's the chip
unfortunately, now it's the end of my workday... so i'll be coming back to this next week...CAUSE ITS QUITTIN TIME
to be continued....
lilshawn:
dug into this a bit more this morning.
checked waveform 12 (h-contol out from IC404) it's good and rock solid.
checked waveform 16 (h-control after sblkout bias has been applied? ...something like that safety blanking (xray protection switch basically)) and it's rock solid.
moved to horizontal yoke drive system
checked waveform 14 output from IC404 (smps control IC) and output is fine at cold startup ... got a weird dropout halfway through the waveform... but picture still seems to look okay. (could have been my connection, I had to extend my probe ground through the chassis with a croc clip wire so HV could have been affecting it)
https://photos.app.goo.gl/FdUtsJhuCQ32a28k7
.. waveform then sketches out when the screen does.
https://photos.app.goo.gl/DUNUkNXaYJCKAMqZ8
i'll probably just swap this IC404 out with another just to be sure... never know these days.
checked waveform 4 (IC404 input for current compensation) and it looks solid enough enough when cold, but it sketches out too when the screen does.
https://photos.app.goo.gl/W9cqsoexY3i2A4X97
moving backwards through the system looks like the input to pin 1 of IC404 is being (eventually) driven by T402's primary side. but not before some kind of "Locking" signal.
so i guess the next place to start looking is whatever this locking signal is coming from (apparently T802 and the main SMPS power supply drive IC circuit... for... reasons?) to make sure it's staying stable and then i guess whatever is driving the primary side of T403
i'm eyballing Q413 and Q314... but we will see.
... to be continued. i gotta do something else for a while.
edit: sblkout is Safety Blanking output. (Activated during frequency changes, when X-RAY input is triggered or when VS is too low.)
also waveform 14 is current compensation circuit feedback into IC404
lilshawn:
looks like that weird dropout I saw was not just a ground connection, as it appears to have manifested in another place, the pulse going out to "locking" signal. it started out good, and i was messing with the scope looking at the waveform closer up and how it changed when the picture geometry change... and it coming back to it i noticed the dropout appeared.
https://photos.app.goo.gl/S2JvhKfVPuQSxv5Q6
i guess i didn't take a pic of it, but i got a clip of it as it's sketching out, and it can be clearly seen as a dip in the beginning of the large peak.
https://photos.app.goo.gl/RpgqYahnPg1oYfBk8
so it also looks like "locking" is some kind of power supply feedback into the main power SMPS IC. not sure if the dropout is from IC404 or the h-yoke predrive feedback through T403, since it's looped around and connected together so it's cause is definitely coming from somewhere around here.
some kind of "hs" pulses (EDIT: Horizontal Size PWM signal) also come out of the main processor IC at pin 20 before heading over to IC404 i doubt it's the cause since it's tied to the blanking and B+ control pins (pins 22 and 23) of IC404 as well as the vertical dc bias control pin 33 and it seems to work in the vertical perfectly, so the signal SHOULD be good. though i still wont discount it since it's related the the waveform 4 I measured as sketching out and had that weird dropout in it. i'll measure right at pin 20 of the main processor IC and see how it looks.
if the main IC output on pin 20 looks good, i will probably just shotgun the area and source a replacement IC404, Q413, Q114 just to spite and see what happens. i mean for the sake of a couple bucks of parts, not a big deal.
if not, i have a trashed chassis here i can yank the main IC off and drop it in to test.
if it's neither... i guess i keep probing
lilshawn:
i started out removing and swapping IC404, i haven't tested it yet, but I thought more about what was going on with what circuits where working perfectly and which ones seemed to have the problem. so i decided to step back for a hot minute.
have since discovered pin 1 with waveform 4 is a current compensation circuit for the yoke drive... and even though it does eventually connect up with the microprocessor HS signal, it's also tied into the E/W compensation circuit, and the E/W circuit and pincushion appears to be working as designed... either that or the amount of change in the signal is inconsequential to those circuits.
I've printed a section of the schematic and started highlighting and marking what was good and what was bad crossing things off the list of things that work... basically leaving that which does not.
I seem to have been left basically the block of components around IC404.
so i'm guessing the problem does indeed lie within IC404, and possibly D426, D425... or possibly also Q404. I'll be checking R438 (150k) R489 (20k) and probably swap a couple capacitors C472/C460/C469 since i have piles of those and the 1n4148 diodes. might as well go over basically this whole block...
lilshawn:
Today, I finally got around to this project again and I threw a handful of parts at this IC404 area to see if any have an effect on the issue.
I replaced IC404, D425, D426 and went through and double checked the resistance values of all the resistors. (didn't find any out of spec) The only resistor i found odd was R415 (22 ohm) and it appears at one time it was a little warm, having some slight discoloration of the casing. It supplies a power rail to this circuit, it's a really low value, and it measured a little on the low side anyway (21.6 ohms)...so i'm not too worried about it since really fried resistors start going UP in resistance.
unfortunately it still has the issue, though somehow it is not as bad? it seems to run quite a bit longer now before starting to sketch out (had to run the monitor 15 or 20 minutes before even starting to see the jitters start to appear)... and when it does, it doesn't get nearly as bad as it did with the whole screen getting affected. It does still have that weird scanline dropout line right in the middle of the screen, and the jittering confined below this line.
this image was taken after about 20 minutes of runtime while i've been typing up this post....
https://photos.app.goo.gl/DXyM2MW6WycT9NLg8
you can see the line is still there... and these jitters look maybe about as bad as it got while it's running. (it's hard to get a pic of CRTs). it could be a fluke, and it's being extra nice today... or my poking and prodding and bending of components to try and read silkscreens to find stuff could have pushed something back into spec.
maybe at lunchtime i'll pick up a can of air duster and turn it upside down and give a few things a blast of liquid CFC and see if it smartens back up if something in particular gets cold again.
other than that... next to get the shotgun is... Q404 C472 and then another run to check. failing that, Q405, Q419.
welp, back to work....
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