Pac-Man Composite Negative Sync Issue - K4900

[Olexo2424]

On the last leg of my restoration on this Pac-Man.

Swapped in a 4900 and tube combo and pulled the 4600 outright to look at later.

Anyway, 4900s you use the horizontal sync pins for composite sync right? It's specifically a 4606 so a later revision. Somebody had seemingly cut one of the negative sync wires at some point as you can. Otherwise I can't get a reliable H hold and blue is dominant in the signal.

 

[Kickman]

https://arcadecontrols.com/BBBB/sync.html Read BOBs guide it's helpful for a lot this topic

 

[Olexo2424]

Yeah I have a lot over the last couple years but this 4900 thing is quite odd and following what the chassis itself says on the monitor frame is what's got me. "If using composite sync, use the horizontal sync pins" so I was thinking okay, logic dictates then I'll only place the connector on the farthest negative horizontal sync pin.

 

[mecha]

Pac-Man uses negative composite sync. traditionally, since much of them came with G07s, the 3 pin sync plug will have a wire bridge between pin 9 negative vertical sync and pin 10 negative horizontal sync. as you can see, someone cut out the pin 9 bridge wire.

the instructions you're referring to are really saying that Wells-Gardner monitors aren't supposed to like the bridged syncs and that negative composite sync should only go to pin 10. on the old analog monitors this isn't really a problem I see, but I only run composite sync to pin 10 on games I work on. on G07s that don't have composite sync routed to pin 9 or haven't been modified the game will have a vertical roll that can't be adjusted out with V. Hold. I personally never have done the mod on the deflection board and just alter the sync plug with the bridged wire connections.

for anyone reading this without a cannibalized sync plug in their Pac-Man, you can move the plug a row over or turn the plug sideways to connect to pin 10 only.

your white balance isn't set right, you have an overwhelming amount of blue and/or the Screen on the flyback is turned up too high. alternatively it could be Black Level is turned too high; this adjustment is actually backwards, meaning clockwise rotation will make it darker and vice versa.

your H. Hold probably needs to be adjusted.

 

[Olexo2424]

Pac-Man uses negative composite sync. traditionally, since much of them came with G07s, the 3 pin sync plug will have a wire bridge between pin 9 negative vertical sync and pin 10 negative horizontal sync. as you can see, someone cut out the pin 9 bridge wire.

the instructions you're referring to are really saying that Wells-Gardner monitors aren't supposed to like the bridged syncs and that negative composite sync should only go to pin 10. on the old analog monitors this isn't really a problem I see, but I only run composite sync to pin 10 on games I work on. on G07s that don't have composite sync routed to pin 9 or haven't been modified the game will have a vertical roll that can't be adjusted out with V. Hold. I personally never have done the mod on the deflection board and just alter the sync plug with the bridged wire connections.

for anyone reading this without a cannibalized sync plug in their Pac-Man, you can move the plug a row over or turn the plug sideways to connect to pin 10 only.

your white balance isn't set right, you have an overwhelming amount of blue and/or the Screen on the flyback is turned up too high. alternatively it could be Black Level is turned too high; this adjustment is actually backwards, meaning clockwise rotation will make it darker and vice versa.

your H. Hold probably needs to be adjusted.

View attachment 863167

Great write up, explains quite a lot, thank you.

So H Hold doesn't actually hold between turning the game off and on.

Blue cutoff is making no difference on the blue level, just more or less blue.

Black adjustment, same thing except essentially darker or lighter blue.

Flyback brightness the same kind of story.

So solder a wire bridge on the chassis between pins 9 and 10 and then move the connector over after fixing the stupid wire in the 3 pin.

 

[mecha]

Great write up, explains quite a lot, thank you.

So H Hold doesn't actually hold between turning the game off and on.

Blue cutoff is making no difference on the blue level, just more or less blue.

Black adjustment, same thing except essentially darker or lighter blue.

Flyback brightness the same kind of story.

So solder a wire bridge on the chassis between pins 9 and 10 and then move the connector over after fixing the stupid wire in the 3 pin.

no

take a picture of how you have the signal plugged in. do you have a TPG to use with the K4900?

 

[Olexo2424]

Nevermind I see what you're saying now. Cold solder on the blue transistor fixed that right up then I was able to dial in everything but H Hold. It's not sync from the board because I put in another 4900 and had no issues. But I'd like to get this one sorted in the H Hold department because it doesn't hold rebooting the game.

 

[Olexo2424]

So I'm back to playing around with this chassis. H Hold can't get locked in. I know it's not a sync issue, this is straight chassis. The other locks in and looks good. For shits and gigs I reflowed solder on the H Hold pot.

 

[mecha]

seek out @paul400

 

[Olexo2424]

@paul400 you have been summoned

 

[Olexo2424]

The based flowchart reference. "Severe, horizontal 'tear' at the top of the picture" I guess best describes the problem..?

 

[mecha]

Substitute IC301

 

[sfspanky]

Substitute IC301

Beat me to it

 

[mecha]

IC301 possesses the horizontal and vertical oscillators. the H. Hold and V. Hold adjustments affect these. I've never needed to replace one on a K4900 but it could just be the chip is bad or got damaged somehow.

 

[Olexo2424]

Alright, 301 swapped from a chassis with good hold. So we'll see here in a bit.

 

[Olexo2424]

Nope. Best I could while still slightly jittery then the same thing upon reboot.

 

[Olexo2424]

Changed C315, no change

 

[Olexo2424]

This is a link to a video of what it's currently doing if you're interested. Hold completely rolls upon reboot.

 

[Olexo2424]

At the end of my skill level

 

[Olexo2424]

Changed H Shift and H Hold pots, no change