Adding Composite Input (Capacitor Question)

[kf4rca]

What source are you using when you see bending. Three quarter and half inch machines that don't have a TBC output can cause horizontal bending. What are you using for a signal source?
I use Paint (in W7) to crop and squeeze my pictures down. Generally I have to go down to 640x480 to get them to post.
Do you think if I donate to the site, they'll let me have more space? Hmm.

[ARC Tech-109]

The bending happens regardless of the source be it from digital or TBC analog, all of my analog tape has dedicated TBC's and everything is locked to a master BB source thru a Kramer VM-1045 distro amp.

Sources are a Sony VO2860A U-Matic that's on a NOVA-800 full frame TBC. The DigiBeta doesn't need any TBC and the Type-C Sony BVH2000/3 has the internal TBC option boards. I also source from a one of those DTV converter boxes and get the same results.

I'm seeing two types of bending, one related to the black subjects and the other bend is fixed at roughly 1/4 down from the top that doesn't move except when I push the horiz hold to the edge before lock is lost.

Going to sub in some capacitors on test probes and see how things are affected.

[old_tv_nut]

Having bending related to black subjects seems to indicate sync clipping at the wrong level, possibly video signal is too small peak-to-peak or at wrong DC level; or, the sync clipper itself is at fault.

[ARC Tech-109]

That's what I'm thinking as well, going to run thru the IF alignment again and keep a close eye on the sync & burst using both the sweep/marker and actual video to see how things are interacting. I'm sure it's something I'm not doing right but can't put my finger on it just yet.

Going direct composite gives similar results however I can't get my DA to go much higher than 1.5V P-P from an unloaded output. It does however make for a very nice picture without all of the lumped bumps from the coils along the way.

You should see what my cat did to the set earlier today, it's posted here on Audiokarma... and I'm not too happy about it. https://audiokarma.org/forums/thread...#post-18377210

[ARC Tech-109]

It's 0200 central and I'm out of ideas. A picture can be worth a thousand words so I did my best to grab a few and crunch them down, if you want larger originals they're available. I named the files to be self explanatory, if something doesn't turn out please let me know.

So what I have is endless frustration with the horizontal and to a lesser degree vertical sync. I've run thru the IF response several times tweaking here and checking for symmetry there, replaced the AGC/Sync sep 6GH8 with several NOS tubes fresh from the cartons and checked resistor values along with probing in capacitors on top of the originals with no changes to the bending.

The signal into the 1st video amp is strong, over 2.5V P-P from the detector and I'm seeing signal levels on the various test points that are very near the spec'd levels in the schematics, horizontal lock is very strong but the vertical is dependent on the size control settings, stretch the vertical to fill the screen and it wants to lock on the black band within the picture itself unless I run a 4:3 image in which case it attempts to lock onto a something near black. Tube is new and I've sub'd in several different NOS tubes with the same results.

Power supply voltages are within 5 to 10 volts of spec and I can't pick out any ripple on the scope. AGC is set conservatively however going for overload doesn't affect the bending as much as it does the overall black and contrast as expected.

Horiz out cathode is shy of 200ma at medium brightness and the 6LQ6 tests at 90% give or take.

In the group of pictures I've included the test pattern I'm using to demonstrate running in as both composite and CH-3 RF. The scope screen shot is direct from the test point TP2 using a 10:1 100 MHz probe and the test pattern itself comes from my Newtek Tricaster TC-550 which is essentially a studio control room in a box. All the output levels conform to NTSC standards and verified using a Leader waveform monitor and vectorscope.

So what this all comes down to really is what am I missing?

[ARC Tech-109]

Just for those who want to see what the set looks like here are a few gems to safely drool over.

[damen]

Sorry if I missed it, but if you haven't yet replaced C511 in the vertical circuit, do try a .03, or .033 there.

[ARC Tech-109]

Complete success.

Found R728 had carbon tracked from what I suspect was an overvolt being it's a carbon film subjected to some 400-plus volts during the initial power on and that particular tube warming up rather quickly. My theory anyway. What I do know is there's a clear carbon burn going from end to end and being on the bottom I didn't see it right away, a carbon comp has since replaced it and the wiggles along with the nagging vertical issue are gone.

Picture quality? Absolutely stunning for 1970 and I've known this set for the past 56 years. Remaining issues? None. A couple of loose ends with the add-on MTS decoder I use in place of the sound discriminator and a mountain of cat hair that's trapped in the cooling fan is really all that remains. What a ride this has been!

So at this stage I'm going to run it for a while and construct the Phil Nelson CT-100 triode based video input adapter that uses the 12AT7 and go from there. It's not a need so much as I have the IF working quite well but now that all the variables have been worked out I can move to the next chapter.

Give me a day or two and I will post more pictures of actual operation and some of what I feed the set with.

Again want to thank everyone for all their help and support. A special thank you to damen and Danny S. for help with the IF board and tuner. Without you I would still be at square one.