K7000 25" vertical jitter when warm

TheShanMan

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Been doing some work on my Pig Out including some monitor work and I haven't been able to figure out this jitter. It's only been happening rarely while I've been working on it in my shop. I believe I discovered tonight that it's when warm. Once I thought of that, I closed up the cab and ran it for a couple hours, and sure enough it happened. I replaced Q9 and I had another IC3 so I figured I'd try that too (saw a post about jitters that was solved by this). I replaced VR3 (v pos) for an unrelated reason, but it happened before I did that too. Also happened before and after recapping.

I have installed a resistor in parallel with R83 to lower the value to 291 because I couldn't center the image properly (Pig Out has an off center plastic bezel for some reason). I've seen posts about lowering R83 for moving the vertical center down further than the pot will allow, so probably that's not causing it although I might pull that out next just to be sure.

It seems like maybe some sort of resonance because the pattern is always exactly the same and just continues on and on and on.

Any known causes for this particular jitter? I haven't found anything quite like this here (lots of other kinds of jitters/bouncing/shaking though).

Probably not hard to see, but the easiest way to watch this is to watch the bottom of the letters of "and press join" relative to the top of the black plastic bezel.

EDIT: to be clear, this is not some sort of blooming issue where the overall size is growing and shrinking. The entire image is bouncing up and down. Bottom (as seen in the video), top, and middle.

 
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I've seen a similar (not as pronounced) shake when some cabs are racked up side by side or behind. Almost as if the other monitor is causing interference. If I pull the cab out the shake is gone. I think at one time or another I explored using a baking sheet as RF shield, but I don't think that really helped.

Other than that, Maybe try another game PCB or see if the earth ground on the power supply is connected to the input ground. Older power supplies with screw terminals have these separated while new AT style units connect them internally.
 
Thank you for the thoughts! I don't have other games running so it's not interfering with another game. I double checked earth ground and yes, chassis ground is connected. Not visibly, but it's 0.0 ohms so I guess it's internal to the Peter Chou. I'm working on a 2 game switcher, and it happens with both games. So it's not the game either.
 
126-127. Because it wasn't actually 130 I tried replacing the regulator and that made no difference. I got the sense that 130 doesn't mean exactly 130. Or does it? If that's where my problem lies, happy to attack it from that angle.
 
I would work this side of the flowchart. Yours doesn't look like a hula, so probably not The VR or filter cap (though cap might need to be changed) Maybe a sync issue or Q7 or C22, or IC2.
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Yeah I've looked over the flowchart and of course nothing really matches up. But a sync issue sounds conceivable to me now that you say it. That's worth investigating. Thanks for the idea there.

Man, the picture is so beautiful otherwise. Thinking I had previously resolved this, I spent much of Saturday dialing in all the color adjustments and re-converging. I was so happy with it, and literally ready to truck it into the game room when I saw it start jittering again. :eek:
 
126-127. Because it wasn't actually 130 I tried replacing the regulator and that made no difference. I got the sense that 130 doesn't mean exactly 130. Or does it? If that's where my problem lies, happy to attack it from that angle.
A genuine vr will hold it at 130v, a counterfeit or remarked vr will give 126volts.
 
Well the old one was probably original, and the new one is from APAR. I don't think the ones he sells could be counterfeit, could they? Good thought though.
 
No, APAR only sells genuine parts. @security0001 goes through great pains to test parts for authenticity. 126 is a bit low for 25" though. I've seen cold joints cause this issue, but you've re-flowed. Make sure that all the things in the VR circuit have nice joints, including the connections to R301 & 101.
 
Yeah that was my understanding. I'll check and reflow in those areas. Appreciate the input on this, and of course I'll report back after I've done some digging in on this.
 
Remove the 2-way switcher and see if that clears up the monitor jitter.

Thank you for the thoughts! I don't have other games running so it's not interfering with another game. I double checked earth ground and yes, chassis ground is connected. Not visibly, but it's 0.0 ohms so I guess it's internal to the Peter Chou. I'm working on a 2 game switcher, and it happens with both games. So it's not the game either.
 
Yeah, will remove the switcher too just to rule that out. I had it running for a good 4 hours this evening and it didn't happen. I even stuffed a rag in the upper hole for the last hour. Seemed heat related yesterday but I still can't say for sure either way. On our next warm day I'll open up the shop garage door so I can get the ambient temp up, and try again.

Again, really appreciate the suggestions from you guys. When I do get it to happen again, I'll have a bunch of things to try. And I'll report back when that happens.
 
Quick thought: Mike mentioned in a recent video that a monitor shake may be an issue with the yoke header. Check the pins for tarnish/rust and maybe reflow them
 
That is a good thought. I hate how tight those connectors fit. So hard to pull off and push on. Every time I (carefully) do it I worry about cracking the solder joints. I might go ahead and reflow them just to be sure. The chassis is in pretty good shape though - pretty sure there's no tarnish or rust, but I'll check that to make sure. Thanks!
 
So I have a cab with a Pandora's box in it and assumed the slight shimmer to the picture was because of the crappy output. I just reflowed the header pins (they looked fine) and low and behold, perfectly stable!
 
@DuffCon Thanks a lot for thinking of me and coming back to this thread. I just reflowed those header pins so we'll see how it goes. I haven't had issues since I first posted about this (of course!) but hopefully now I never will.
 
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