Which game? Mike Pacak and/or Steve Young may have the schematic.
How was this one scanned? With a potato? Perhaps some photoshop adjustments would provide clearer text. Start with the b/w levels.

Do you have the PCB? You can use that to see what's what.
The buffer on the left are easily a 7407 chip.
The right could be a 4051 multiplexer.

It's tough to enhance a copy of a copy of a copy. You'll have to fiddle with it in photoshop if you can't track down an original. But, it's not going to get a whole lot better than that.

Can you show what an unaltered scan looks like? Usually, if the paper is yellowed, that can help somewhat.

If that's all you have to work with, it's legible enough to see what most things are, and figure out others with some guesswork along with the PCB (assuming it has a complete masking layer with everything labeled).

Maybe recreating the schematic in KiCad or another PCB design software would better than trying to touch up a fuzzy print/scan.

Useless skill number 43:

Spend enough time reading blurry schematics and everything just makes sense. That must be a 4051 mux/demux, so pin 16 is VDD even though everything at the top is blurry, because its at the top and connected to +12v. When you see a resistor it must say R## and #.#K, and that's how you start.

Maybe there is another pin with similar schematics that are clearer?

I have some photoshop skills but the example you posted makes me think that redrawing the schematic would be a better option. To really do it right you'd redraw a portion and post before and after versions and let the forum look for mistakes. Captcha ("I am not a robot") does the same kind of thing by letting a large group of people determine what's in an image.

I'd be willing to experiment a little to see what options might work. PM me if you're interested.

/Mark

Don't forget, there are more tricks to decipher the illegible parts of the schematics. If you cant read what IC7 is or are not sure what size resistor is connected to pin 11 in the schematics, just look at the physical board to confirm. You also have the data sheet for any IC to identify/confirm the pin numbers and function.

here's the visible layer I've traced out so far on the schematic. I will likely need ID's on the parts once I get to putting the text labels in. Still have to add components and arrows - I have all those as text characters somewhere so that's going to be part of the final steps.

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You left out the resistors which changes the function. Are the input pins of IC7 pulled high or tied high, etc?

Draw 1 resistor and paste where needed:

with resistors (resized).png

Also there are 3 identical MUX/DEMUX chips but I noticed you redrew those 3 times. You could have just copied and pasted the first one over and over, but I guess with the tracing that gets tricky.

That's why I said in my post "I have to add the components yet". The tracing so far is about an hour's worth of work. The component insertions will go very quickly as they're a font, and once I have one horizontal one and one vertical one rasterized with the whitespace inserted so I can avoid having to do an erasure on the main drawing layer, they will lay down extremely quickly.

The original scan is extremely skewed at places so tracing is working out better. I'm not actually recreating the schematic in a schematic type program (If I had/knew how to use one I probably would) - I'm literally tracing over the original scan John sent me in photoshop but correcting for any deviation from 90 degrees. (I'm not even using Illustrator which would make more sense being vector based, because I'm self-taught on how to use the pen tool in photoshop 6, and it doesn't work the same way in Illustrator (at least the versions I have access to which are all old circa 2004 versions).

I've used this exact method in the past to clean up scans of schematics and gone to Staples and done an 'engineering print' which costs about $6 but can be as cheap as $3 if it's smaller. Nothing drives me crazier than illegible schematics posted to various places, or even worse, when you order a schematic from a supplier and it's a crap printout with fold marks etc. all over it.

I have Williams Ringer already done if anyone needs it, and a couple other games are in progress. Motivation tends to flag sometimes in this type of project but it's something I always get back to when I have roadblocks in other projects.

Cool. Sounds like you have the process and tools well worked out.

You are doing what I was going to do, trace. I Will let you continue the good work.

here's some more.... just have to add most of the caps and grounds. obviously this is a clip. Next up will be the hard part which is identifying the correct values for the components for this I will need help from someone who has the board available. There will be questionable parts I'll highlight in red and send the file to whoever can help there since I don't actually own this game.

pasted_image (resized).png

Another thing that sucks with copies of copies of copies is you start to lose or gain the junction dots. Causes the.... hrmm are those crossing over or electrically connected.