ms pacman blue backgroud

dandydan1959

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Hi,

I am working on a original pacman with ms pacman mod. I have solved several items with this mostly relating to edge connector and hum bars caused by the fuse block. The last issue I have is a blue background screen. All characters are there and I see colors such as yellow, red and the letters are white as they should be but the background is not black but is blue. Any help would be appreciated.
Thanks
Dan
 
I would try turning down the Screen control on the monitor. If it's up too high, the screen will glow a blue-ish color.

Use a non-conductive tool to adjust the screen control.
 
if EagleTG's idea didint work try a cap kit


PS: I AM NOT A PRO

PM ME WITH ANY NEWS OR ANYTHING!!!!!!!!!!!!!!!!!!!!
 
pacman blue screen

I got around to trying a different monitor last night and the blue screen is still there after the swap. I also disconnected each color last night one at a time from the monitor input and when I pulled the blue input the screen background turned black and the maze colors were correct. I am moving on to the 3B suggestion assuming the blue signal from the PCB is the culprit. I am not sure how to determine if 3B is bad so I am going to need to do some more research. I have a logic probe and and multimeter. I do not have a O'scope but have been looking for one on CL. I am going to poke around the sites dedicated to Pacman and see if they mention troubleshooting tips for this. Any help from you guys would be appreciated.
Dan
 
On any color issue like that I would at minimum pull and reseat the color proms 4A and 7F first. Alot of times these sockets need to be replaced but reseating the proms can get it going sometimes. Did you clean the edge connector of the pcb? I have seen ones that look fine but after cleaning the issue was fixed. A quick hit with #000 steel wool will knock off any corrosion from the edge fingers. Please, dont use sandpaper!
 
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pacman blue screen

Hi Guys,

Edge connector is clean and bright. All functions work except for original blue screen problem..

I have pulled and cleaned the 4A 7F chips and checked continuity for their sockets from the chips to the solder side of the board. Also checked connections to 3B and 3A and all circuitry around them. I still have a blue background screen with all characters and maze colors correct. I am going to post pictures when I determine how to do it.

How do I check 3B's operation? I have a logic probe. Can I check it against another chip for comparison?

Thanks
Dan
 
Let's start by checking the voltage of the blue output signal at pin U of the edge connector. It should be about 2.5 volts, if I remember correctly. It's probably higher than it should be. Then you can trace it back through the board to see what is causing it to be so high...
 
Thanks for the help

Hi guys,

I have been able to locate my problem and correct it using your expert help and support. the board had a solder splash from pin U to pin V which was putting the 5 volts from V on the blue pin. The background is black and the maze is correct.

This is my first board repair and I learned a lot. These boards will test your confidence since they can be so unpredictable. The edge connector touch up I did helped but in doing so I created this issue as well. Lesson in doing too much all at the same time.

thanks again,
This was a fun and frustrating project that I am doomed to repeat.
Thanks
Dan
 
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