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  #76  
Old 07-10-2017, 07:47 PM
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VintagePC VintagePC is offline
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That's what I initially thought too, but if you look closely the raster scan lines actually follow that curve instead of fading out like they would for bad centering or misaligned ion trap. Slightly visible here at full resolution, but not great, the trace lines always seem to come out overexposed on my camera.

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  #77  
Old 07-10-2017, 08:20 PM
EdKozk2 EdKozk2 is offline
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Did you follow the horizontal frequency and drive adjustment procedure from your schematic? From your video it looks as though the horizontal lock-in and drive are not set correctly, even though your double peak sine wave looks good. It also seems is if there is a loose connection when you tap the screwdriver. A faulty tube could also be the culprit.
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  #78  
Old 07-10-2017, 08:36 PM
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Yes, I'm trying to follow those steps but it is not locking at all. I was able to do it fine with the set on its side, so I do know how it's supposed to go.

All signs point to a loose connection but I have not been able to locate it; everything I ohm out seems OK.

Perhaps it is not a completely loose connection but a high-impedance one instead; that would explain why I can't find anything checking resistance but it acts up without fail at 15 kHz... that's gonna be tricky to find.

Am I right in thinking that it's the horizontal waveform coil that creates that double-hump shape? If so, perhaps that's the place to start looking, you can see it goes away leaving only the horizontal drive sawtooth sometimes when tapping.... perhaps that coil is going open circuit.
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  #79  
Old 07-10-2017, 08:46 PM
EdKozk2 EdKozk2 is offline
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A loose or bad mica cap at the horizontal coil could cause the saw tooth wave form. Did you oil/ lube the drive pot? Checking with a meter doesn't always verify a good pot.
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  #80  
Old 07-10-2017, 08:54 PM
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Yes, I got all the controls early on with deoxit and verified they turn and change resistance smoothly. Good point on the mica caps. I know they usually don't go bad but it is possible.

Thanks for the suggestions, will dig some more tomorrow and report back.
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  #81  
Old 07-11-2017, 09:00 AM
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Electronic M Electronic M is offline
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Quote:
Originally Posted by EdKozk2 View Post
A loose or bad mica cap at the horizontal coil could cause the saw tooth wave form. Did you oil/ lube the drive pot? Checking with a meter doesn't always verify a good pot.
Another pot related issue it could be is tin whiskers. Cleaners and lube often won't clear tin whiskers.
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  #82  
Old 07-11-2017, 10:01 AM
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Notimetolooz Notimetolooz is offline
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That divot thing is weird, I think it has something to do with the crt geometry, they probably will go away when you get other things straightened out.
I kind of suspect the horizontal coil also. Maybe you can localize the problem by using a small wooden dowel and tapping various components. Could be tube socket, capacitor, pot, etc. Is it still shock sensitive when you swap tubes?
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  #83  
Old 07-11-2017, 11:13 AM
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Quote:
Originally Posted by Notimetolooz View Post
That divot thing is weird, I think it has something to do with the crt geometry, they probably will go away when you get other things straightened out.
I kind of suspect the horizontal coil also. Maybe you can localize the problem by using a small wooden dowel and tapping various components. Could be tube socket, capacitor, pot, etc. Is it still shock sensitive when you swap tubes?
I think the divot is a "charge bubble", which was sometimes seen on un-aluminized CRTs during warmup or other times when the HV is not stable.

Agree.... tap everything in the horiz circuit.

jr
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  #84  
Old 07-11-2017, 05:58 PM
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Success! Swapped the horizontal oscillator for the one in the vertical sync circuit, and my horizontal problems went away. (Well, the width coil still doesn't do much, but the major ones are gone)... and now my vertical is sensitive to vibrations. This is one of the original three, I'm guessing it must have been the one not being used as an oscillator. Certainly a red herring chase... it was so damned sensitive it would change frequency/drift if I blew on it... or tapped literally anything. Yeesh.

Apparently that one 6SN7 is just very microphonic. Why are replacements so damned expensive? (*glares at audio crowd*)

Still no idea what's making it the horizontal chitter on startup though (like the first video I posted). I guess if it's not likely to hurt anything it's not a big deal, just curious.
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  #85  
Old 07-11-2017, 07:19 PM
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Notimetolooz Notimetolooz is offline
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Great news! That tube must be more than microphonic if turning the chassis on its side effected it. Must be something really loose inside!
"Charge bubble" is a new one on me. I guess I learned something new today.
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  #86  
Old 07-26-2017, 08:26 PM
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After acquiring some more 6SN7s and eliminating the vibration-sensitive one, the funny business is back. I swapped out the horizontal oscillator for the four ones I have now, and I'm still seeing funny business like weak HV, blooming, etc... and I doubt that all of my 6SN7s are that bad. I'm left scratching my head because the symptoms aren't consistent with changes I make - e.g. swap the damper, picture is suddenly dim and blooms. Swap it back, it doesn't go back to the way it was before.

Having had suspect HOTs and dampers already, I need to pick some expert brains... What kind of symptoms can one expect for weak:
-> H. Oscillator
-> Damper
-> H. Output
Specifically, are there differences that can help me ID the culprit(s) without a tester, or are those symptoms all over the place?
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