Strange problem with Nanao MS-2931

[Trozze]

Last month I got my first Sega Blast City, it sold as “monitor not working”. When I got home and powered it up the monitor worked, the previous owner told me that someone had tried to repair it before, so I wanted to look at it before running it too long so I shut it off.

I disassembled the whole cabinet to clean, remove rust and repaint the affected parts.

After removing the CRT Chassis, I immediately noticed that someone had... "Repaired" it. They have replaced the HOT, one cap and a transistor. All the pads were ripped away.


Warning for Graphic images!!

After tidying that mess, I replaced all the electrolytic capacitors on the board+neck with new Panasonic and Rubycon capacitors.
When I turned the monitor on I heard a POP and a capacitor vented.. I managed to put one on backwards... :/ So I replaced it and turned it on again.
The picture looked great, until after a few seconds when I got into a game. I noticed some horizontal distortion on the bright parts of the picture.


I tried to capture it with a full white picture, you can see it flickering if you full screen the clip and look at the bottom section.

I have checked every cap for the correct rating and polarity, and all the solder joints. I have also reflowed the whole neck board.
I used the MS-2931 manual and Schematic to diagnose the board, but I cannot find any problem.
I've noticed two things: the flyback is making a high pitched noise, and the CXA2055p is getting hot really fast.


Have you ever seen this before? Is this a problem with the tube, yoke or the chassis?

 

[djsheep]

Damn. That solder job is the stuff of nightmares. Hopefully someone here with experience can help you out.

I feel really lucky to be in Australia and have access to Jomac’s services. His turn around is 24-48 hours on chassis and they’re ALWAYS fixed.

 

[ekorz]

I had that kind of horizontal distortion once with my Blast. My video source was an improperly grounded mame pc. Not sure what you’re using but maybe check that everything is grounded appropriately.

And just pointing out that “that mess” was using solder to connect a pins that were on the same ground plane. Maybe the original pads were burnt and the only way to ground those components was to tie them into ground somewhere else. It’s inelegant, but a blob of solder to a nearby intact via does the job. I’d grab a multimeter and confirm your “fix” is grounding those components.

 

[Trozze]

I had that kind of horizontal distortion once with my Blast. My video source was an improperly grounded mame pc. Not sure what you’re using but maybe check that everything is grounded appropriately.

And just pointing out that “that mess” was using solder to connect a pins that were on the same ground plane. Maybe the original pads were burnt and the only way to ground those components was to tie them into ground somewhere else. It’s inelegant, but a blob of solder to a nearby intact via does the job. I’d grab a multimeter and confirm your “fix” is grounding those components.

Thank you for the suggestion, I will check the ground when I get home!!

Yes, it might be that the pads were burnt away, but I couldn't se any burnmarks around the area. The long negative leg on the first picture was floating due to a cold solder joint.
I have checked all connections with my multimeter, my next step will be checking the signals with my oscilloscope.

 

[nem]

Yeah, could be some outside interference not related to the monitor.

As for the lifted solder pads, it's sometimes unavoidable. Some components like transistors and resistors run really hot and when you try to replace a faulty one (or even test an unknown one) the pads can come right off. However, in the above pictures, most likely whoever was doing the fixing likely had the soldering iron on too hot. The PCB would be noticeably discolored if it was a "hot spot".