Ms Pacman instantly clears levels

[VforVash]

Hey everyone, just registered because of this issue. I'm working on a CT that at one time (about 10-ish years ago) worked. I've been fixing old wiring issues and have got the game 99% working. The biggest issue I found was that the player select buttons weren't working. I replaced the ground wire connectors in the 9 pin molex and the edge connector. The buttons work, but now if you push right on the player 1 joystick the game clears the maze as if you finished it and proceeds to the next level. While comical, after awhile it gets boring not being able to go right. The player 2 joy works fine.

In my searching for the cause of the controls not working in the first place I did pull the 74LS367's at 8E and 8H to inspect/clean the legs. When I was removing each chip I did bend a couple of the legs (I knew better than not using a IC puller), but was able to bend them back. I'm not sure if either of them would cause the issue I'm having.

I also put the game into test mode and the ram checks out ok. Thanks for the help and I enjoy John's videos.

Edit: After looking again, the chips were the color proms at 4A and 7F.

[iankellogg]

check the dip switches. There is a dip switch that will enable SERVICE mode that does exactly like you describe.

[John's Arcade]

I think you want to look for the "rack advance" setting.

[iankellogg]

I think you want to look for the "rack advance" setting.

thank you, couldn't remember the name!

[VforVash]

Thanks for the input, it got me going in the right direction. The dip switches were in the correct position but the circuit diagram led me back to the 74LS367 at 8E. Turns out I was a little over zealous in re-flowing the solder and shorted pin 7 (which ties to the ground bus) to the trace between pin 2 and the dip switch. So, all is good on the joystick front.

Now on an unrelated note. The game has no red. It went out shortly before the game got unplugged and stored. I wasn't sure if it was the monitor or not but, I got a replacement screen from twobits.com and still no red (was going to replace the screen anyway for burn-in and weight reasons). The wires are good between the board and the plug. Just wondering where to start looking and what I'm looking for.

[P-feif]

Replacement screen or just the picture tube? Mine has the same issue. I'm crossing my fingers that it's the transistor for the red circuite on the neck board. In my case I fiqured it needed to be capped anyhow so I just ordered a cap kit and color transistors and some other bits and pieces and just decided to replace it all and see what happens. It's all appart now and I'm just trying to find time to get back to it.

[iankellogg]

There is a resistor ladder for each color on the game board with a shift register I think. I don't remember the exact chip.  I would double check that you are sending red to the monitor before investigating the monitor.

[VforVash]

Replacement screen or just the picture tube? Mine has the same issue. I'm crossing my fingers that it's the transistor for the red circuite on the neck board. In my case I fiqured it needed to be capped anyhow so I just ordered a cap kit and color transistors and some other bits and pieces and just decided to replace it all and see what happens. It's all appart now and I'm just trying to find time to get back to it.

I got a LCD replacement. The old tube was burned in pretty badly and it was a pain hauling it up and down stairs. You might want to try cranking the "red cutoff", if the screen is good, at some point the picture should have an overall red appearance. If not then you might have something in the boards on the monitor.

There is a resistor ladder for each color on the game board with a shift register I think. I don't remember the exact chip.  I would double check that you are sending red to the monitor before investigating the monitor.

So what should I be looking for on the red output from the board, an AC or DC voltage or a particular waveform? The rest of the circuits have been easy to diagnose as I check continuity, then check for the proper voltages. The chips in the monitor output circuit I'm less familiar with.

[iankellogg]

it would be a signal between 0V and 3V. I think with a meter on AC you should see something above 0V.

[VforVash]

it would be a signal between 0V and 3V. I think with a meter on AC you should see something above 0V.

I'm getting 6-7V on all pins to the monitor.

[iankellogg]

Hmm. Not sure on that one. But none the less I think you have red going to the monitor. Next I would try to turn up the red all the way and see if it does anything. If not you need to look at checking the gun and color drive transistors