Naomi Universal - Top Left Flicker (Sanwa 29E31S)

[daveheats]

Hi all,

Looking for a bit of guidance on a Naomi Universal Sanwa that’s giving me a stubborn issue.

There’s a flicker/shimmer predominantly in the top left corner but also visible all along the top 15% or so of the screen.

It moves with the image when I adjust V SIZE — so it’s not fixed to the tube, it follows the raster. It also doesnt change when everything is warmed up, so guessing its not a dry joint.

What ive done so far:

All electrolytic caps replaced
Reflowed remote board
New vertical IC
Reflowed main board

Ill attach a video showing the issue. Has anyone out there come across a similar fault at all?

Thanks for any info!
Dave

Video here

 

[gunblade]

i can see alot of convergence issues but no flicker
in general things like ballasts can cause a wobble in one particular area
important to note what version flyback is in the chassis as a lot of the aftermarket versions had oddball issues

 

[daveheats]

Hiya mate, yeah working on the covergence at the moment. Have got it nailed in the centre, and will be using some strips to sort the corners out.

I'll aim to get a better video of the flicker as in hindsight it's not particularly visible in the video I shared! Also, I've just checked and it looks like the flyback on my board is a E177707 (BSC24-0107). After a quick google it looks like this is the correct part for the 29E31S?

 

[gunblade]

yes correct flyback but is it an original or a later reproduction, photo will prove it

 

[daveheats]

Excuse the blurry photo, but this is the flyback that's in there.

 

[gunblade]

thats an original so no issues with that

 

[daveheats]

Good stuff, glad there isn't some dodgy Ali Express flyback in there.
I'm wondering if it's potentially a resistor or diode near the LA7838 perhaps? Or maybe a failing ceramic cap?

I've just about sorted the convergence, so really hoping I can sort this annoying flickering!

 

[gunblade]

never seen that fault and i have worked on hundreds of these, not something a simple as a dodgy vertical linearity pot
if i could see the actual issue it would be helpful

 

[daveheats]

Hiya mate, its surprisingly difficult to get a video of it, as it looks much more subtle when viewing it back on my phone. But hopefully this video is a bit better:

New video · Tuesday, Apr 14 🎬

Tap to view!

photos.app.goo.gl

 

[gunblade]

that pulsing?

 

[daveheats]

Yeah, thats it. A pulsing / shimmering/ flickering.

 

[gunblade]

whats about that in that area, any sort of ballast?

 

[daveheats]

whats about that in that area, any sort of ballast?

Hiya mate, since your reply I've been busy looking into this more, and so far still no improvement. I've checked the VLIN pot and replaced it (all other pots testing OK), tried with and without the original marquee light + ballast and with and without my new LED replacement bulb, checked all resistors and film caps around the LA7856, and also about to socket and test a replacement LA7856 today, just incase.

I've tested the monitor with my dreamcast hooked up too, just to rule out the Naomi, and the issue is still present, so it's definitely a chassis issue.

Can you recall any other potential source of a fault like this? I am starting to wonder if it could be the remote board?

 

[jerryspaghetti]

I'll bet that its a grounding issue or interference from something in that area.

I am experiencing a similar issue on a cab where the audio amp is near the left side of the screen and if i pull the power from the audio amp the flicker goes away.

Gunblade mentioned a ballast and I believe there is one for the marquee light on that cab. If you pull the power cable from the light fixture does it solve the issue?