Sega Naomi video problem

Here is a quick fix to what I believe is a common Sega Naomi video problem.  I've seen this happen on two Naomi motherboards I own, as well as on a Hikaru motherboard.  Video looks to be smeared or ghosting, like in the picture below.

I don't know exactly how it happens or why (I'm too lazy to really investigate at this point), but the problem is with the filter board (not the motherboard).

After removing the filter board, turn it over and you'll notice a burned trace just under one of the long connectors.  This pin is one leg of an RC network that goes to the VGA port, and then runs under the connector to another set of pins above it.

The fix is simple, jumper the two connectors to bypass the burned trace, and your video will look crisp as new.

Happy gaming!

New Years resolution

With the new year comes resolutions, and this year I am pledging to learn how to diagnose and fix common PCB failures.  Over the years I've been steadily contributing to a collection of broken PCBs, some that I think could be fixed easily, and others that I think require deeper investigation.  Not having an EE background, I've had to learn much of what I know on my own, and will try doing more of that this year in troubleshooting circuits.

The most common failures with PCBs I've noticed, happen during handling: be this incorrect packaging during shipment, or incorrect storage, or even the act of plugging them into a jamma harness inside a cabinet.  In all these cases, the PCB flexes, causing solder joints or traces to crack, or pins on SMT chips to lift from their pads.  Very few failures happen due to static electricity (ESD) while handling...of course this is my own observations, maybe I'm just more careful than most when it comes to ESD.  Lastly, environmental situations can cause a PCB to corrode, or capacitors and batteries can simply leak over time.  There isn't much we can do about this, other than look for the warning signs and then take action.

So I kicked off the new year with buying a Weller WESD51 soldering iron, as my previous Radio Shack 15/30 iron wasn't up to the task of  soldering delicate SMT chips.  I also invested in building a bench top supergun consisting of PC power supply, jamma harness, CGA-to-VGA upscaler, and rotatable small/cheap LCD monitor.  I'm not worrying about input controls at this point as the broken boards I have can't boot up or have graphical glitches that are noticeable without playing the game.

Above is a pic of my bench with a broken Alcon PCB.  The monitor is a small 15" HP 1502 that I got for $30 shipped, I then mistakenly bought an incompatible HP rotatable stand, and had to hack the monitor up a bit to make it bolt to the stand.  I would recommend finding an HP 1530, as its the same small monitor but comes with a rotatable stand and stereo speakers built in.

Next is a standard CGA-to-VGA upscaler you can find on eBay for $35-$40.  I bought one that came with a jamma adapter and RGBHV and power wires for an additional $25.  This makes it very easy to hook up to any jamma harness with an LCD or VGA monitor.

Last, I bought a jamma harness with PC power supply, and provided my own 8ohm stereo speaker I had laying around.

So far I've noticed this setup isn't compatible with games that use a refresh rate below 60hz such as the Raiden series, and a few miscellaneous games.  I am investigating some really fun alternatives to this setup, so stay tuned.