Nanao MS9-29SU horizontal sync pulse problem

[Aurich]

I have a MS9 that was working fine, and one day developed this horizontal sync pulse problem. Video of the issue here, the screen breaks up in wavy sections:



Recapped the whole chassis, because always a good place to start, no dice. Checked for cold solder joints, did find a handful, reflowed them. If there are any specific places you think I should reflow even if I'm not seeing a visual because they seem like they might be related please let me know.

The H.H15 pot was glued down, broke the seal and adjusted it just to check, can get the usual bad sync from pushing it too far, but doesn't help anything.

Replaced the LA7853 sync deflection IC since that seemed a likely culprit. No change. Did the vertical deflection IC LA7837 at the same time, just to be safe, even if it seemed unlikely to be the source of the problem.

I'm out of ideas at this point.

If anyone has any further suggestions I'm very open them!

If the issue is the LA7853 then maybe whatever cause it to go bad in the first place is also affecting the replacement, but not sure what that could be. It seems unlikely my replacement IC was already bad in the exact same way though. Here's a pic of the problem if you can't load the video:

h-pulse.jpg

[grantspain]

i have the an5551 at U450 cause very odd sync faults in the past

if you remove video and up the brightness does the raster remain stable?

[Aurich]

i have the an5551 at U450 cause very odd sync faults in the past

if you remove video and up the brightness does the raster remain stable?

From researching the problem it's clear you're very experienced with this stuff, I will check this and report back, thanks!

[Aurich]

Alright, got an update, and it's getting interesting.

Fired up the monitor with no video, and went to turn up the screen to see the raster lines. Turned it a little too far and kicked in the protection circuit, heard a click and lost neck glow, managed to freak myself out. Turned everything off, lowered screen, turned back on, everything fine. I did curse for a minute there though.

Okay, so I have raster lines, and they're definitely rolling. But then I remembered I had tried playing with the H.H.15 pot earlier, and it might just be normal horizontal hold being off. Tried to adjust it, but with just white screen and raster lines it was too hard to see.

So I went ahead and powered on the other cab this one was slaved to to get a video signal so I could see. And yeah, it was definitely horizontal hold garbled, so I adjusted the pot. And ... suddenly got a stable picture. I could see the game clearly, no waviness.

Geometry was a mess from trying things earlier, went into test menu to get mostly sorted, and this is where I ended up:

IMG_4568.JPG

That's progress! After getting a mostly tuned up geometry so I could see properly I went back into the game attract mode. At this point it's like 90% working, but I do see some occasional little sync flickers in from the edges. It's not magically 100% fixed. But now I'm wondering if that pot was the source of the issue all along? I can't think accidentally going too high on the screen did anything.

I haven't messed with it further yet, calling it a break for lunch now, and I admit I'm slightly afraid to touch that pot again now that it's kinda working lol. But not feeling at all confident about this 'fix'. Maybe this is enough data to draw some conclusions though?

It's not that easy to spot the little flickers, but there are still present it you watch carefully:

[Aurich]

Isolated one of the little artifacts from the video so nobody has to waste their time watching it looking for them, they're pretty infrequent:

chun-sync.jpg

[grantspain]

is the picture affected by tapping the chassis with a screwdriver handle?

[Aurich]

is the picture affected by tapping the chassis with a screwdriver handle?

Just checked, it is not affected. Tapped in several places, including on the pots. Already cleaned up all the cold solder joints we could see too.

Also, this time while I had it on I screwed around with the HH15 pot. And whatever 'magically fixed itself' I cannot get it to come back now. Turned the pot fully back and forth, could get the usual horizontal hold stuff to happen, but the major problem did not return. Just these new occasional little horizontal sync flickers.

So I honestly have no idea why it stopped being so bad. Is it all possible it's related to over turning the screen knob and tripping the protection circuit? That seems weird, but it's the only thing that changed.

[grantspain]

out of interest have you checked with a different game board and also checked the video ground continuity to the jamma and the psu voltages?

[Aurich]

Yes, multiple game boards, and I've also tested the monitor in multiple cabs, just to make sure it wasn't some kind of weird incompatibility. Same behavior. I will confirm ground instead of assuming though.

I'm a bit flummoxed by this new behavior, why it's 'partially fixed' without any reason. I hate it when things change and I don't know why, makes troubleshooting that much more difficult!

Appreciate the suggestions though, I know it's not easy to try and diagnose a problem you can't poke at yourself.

[grantspain]

did the chassis have any cap leakage at all, like a greasy film?

[Aurich]

did the chassis have any cap leakage at all, like a greasy film?

Not that I recall, no, I think we'd have noticed when recapping it.

Still will look more carefully for corrosion issues.

[Sehrlange]

Hello, I do have a horizontal hold issue with my MS9-29. The problem is intermittent though. When I tap the side of the chassis, the problem is resolved, but it comes back whenever I work too hard the joysticks on the control panel.
I read something about tapping the PCB, but never found the actual solution to the issue.
Please advise, and Thanks for the attention to this post.

-H.R.

[grantspain]

Hello, I do have a horizontal hold issue with my MS9-29. The problem is intermittent though. When I tap the side of the chassis, the problem is resolved, but it comes back whenever I work too hard the joysticks on the control panel.
I read something about tapping the PCB, but never found the actual solution to the issue.
Please advise, and Thanks for the attention to this post.

-H.R.

bad solder joints i expect

[Sehrlange]

Any particular spot / component to look for bad solder joints?
-HR

[grantspain]

the most common place for bad solder joints on ms9 is the horizontal drive transformer but loss of hold could be sync in pin or something in sync circuit but you will need to look over entire chassis with magnifier

[cruzlink2]

Hey guys, I had a chassis with the same exact issue. I cleaned recapped and reflowed and it was still the same, then when I went to reflow the hdrive transistor I found all 3 pads wer disconnected. Reflowing that completely solved this issue.


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