Donkey Kong PCB with on-board non-inverted video

[Sock Master]

I needed a 2nd DK PCB set that I could use at my electronics bench for testing DK Remix boards.   I'm just using an old 15Khz RGB monitor so when I saw this board I jumped on it.

It's a TKG4-11-CPU.  It's not the cleanest board, but it's the only one I saw that actually had all the extra components in the analog video section - the extra components to generate *non* inverted video.

Curiously, even though it has all the extra transistors, resistors and capacitors to generate non-inverted video, it is lacking the variable resistors to adjust the RGB levels.   It's also lacking the variable resistor to set the amplified sound volume - but *does* have the components for audio amplification as well.

So.. I re-strapped the video to switch it to non-inverted RGB.  Soldered in some resistors where the variable resistors are supposed to go, and boom..  non-inverted video!

Ok... but the video quality actually looks kinda crappy.   There are strange dark smudges above some objects, and strange light smears of color inside some objects.   The photo shows the dark smudges a bit but it was actually hard to get it to register in photos.

I suspect I'm going to have to adjust some capacitors or filtering..  More updates soon.

Does anyone know how uncommon it is for a TKG4 board set to come with the extra components for audio amp and non-inverted video?   

[Sock Master]

I figured the streaks in the non-inverted video output had something to do with capacitors, so I started digging around in the re-inverter (invert the inverted video) circuit.  My first guess was that C73, C75, C77 were blurring the signal so I pulled them up.. but it didn't improve the picture, so I put them back.

My next guess was to add tiny filtering capacitors to the existing circuit.   I added some 10 picofarad capacitors between some of the resistors in the transistor stage.   Bingo, the picture is sharp again.    Ideally I think 7 picofarad would have worked better but I don't have any of those on-hand.

The capacitors I added are the small bright orange ones tied to the ends of two resistors in each color stage.

Photo 1 - close-up of video before
Photo 2 - the added capacitors
Photo 3 - close-up of video after
Photo 4 - the full screen

I have seen mention of other people seeing 'dark halos' above sprites and other objects.  A similar solution would probably do the trick.   (Except in your case the capacitors would go somewhere in the Sanyo monitor's color inverter circuit..  which is probably very similar to the un-inverter circuit on this DK PCB.)

Also of note, in the before picture DK also has light areas under his arms (and weird smeary teeth).  This fixed that too.   W00t.