PCB Repair Help - MikesArcade Pacman Repair Log Interpretation needed?

[francoisadt]

Hi Donkey Kong Forum

Not all hobbyist and knowledge able experts in arcade gaming read all over. To catch an answer:
I am desperate for answers and have posted the below here and at Arcade Game Forum.


I have bought two Ms. Pac-Man PCB from MikesArcade about 5 years ago via the assistance of Mark Hoff. He did buy it for me, and my brother in the USA brought it to South Africa when travelling to his family in South Africa every 2 years or so.

One Ms. Pac-Man PCB the normal speed one do give strange colours repeated bootup. I only have the speedup one in my cabinet now.

When I read MikesArcade repair logs I want to understand what you have written.

This will enable me to try self service my PCB, It will cost much $$ to sent PCB out from SA to USA and back. I do not have that funds. Also with corona virus I am not allowed to sent or receive any postage other than essential foods.

Please take time to answer my questions below, it will assist someone far off to have a working cabinet which have no one else to go to. No arcade hobbyist here  in SA know how to fix the PCB nor know/understand the meaning of what is written. I have asked them.

On Mikes Arcade site :
https://www.mikesarcade.com/arcade/pactrouble.html


Some brief notes are posted above the page as:
==============================
https://www.mikesarcade.com/arcade/pactrouble/Image43.jpg
Abbreviation Example: 2A p1 short to p2 (Chip 2A pin 1 is shorted to pin 2)
Low means grounded - High means +5V


On one screen the following text are printed, what are this mean:

Fault description fix:
No characters on screen. Dots can be seen being eaten.

From Website Example TEXT:
/**********************************************************************/
Caused by interfering or grounding databus RA0 thru RA5.
These can be found on 2A,2B,2C,2D p2,3,4,11,12,13, or 1E p11,12,13,14 or 2E p13,14.
2B p1 is high, or p2&3 or 3&4 or 4&5 shorted.
2A p12&13 or p11&12 shorted.
2E short pin7 to p10.
1E, 2E p15 shorted to p 11,12,13,14.
3D Bad or Removed.
3A, 3B p1 low.
3B p1 short to p8.
Signal 3E p6 to 3A,3B p1.
2F 10,13 low.
/*************************************************/

Now the Questions:
From TEXT: "2A,2B,2C,2D p2,3,4,11,12,13"
Meaning:  RAM position 2A?   and pin 2 , pin 3 ect...
A) What does this mean "interfering or grounding found at these RAM chips" ?

B) FROM TEXT: 2B p1 is high, or p2&3 or 3&4 or 4&5 shorted.
Question: What does it mean RAM 2A pin 1 is high? Does it mean higher than the 5V+ than what it should be? How does one fix this?

Question: What does it mean pin 2 is shorted? How does one fix this?

C) Another Example:
TEXT IS: "Chip 2A,2B,2C,2D 6 MHz clock signal pin 14 is grounded."

Question: What does it mean pin 14 is grounded? What should be done here?

Another Example: Red Background
Signal from 4A p12 to 3A,3B p14 low.

D) Question: What does it mean "low", is it "voltage is low? If so how does one fix voltage low at a specific RAM pin?  One cannot make the voltage coming in too high othewise other RAM chips get more than 5v, so what must one do, and why is some chips pin high and some low?



Another Example:
TEXT: Light red haze over entire screen.
Signal from 4A p11 to 3A,3B p11 high.
E) Question: What it mean RAM 4A is high? High voltage? , if high then how does one fix this?


Another Example:
Random garbage on screen.
Problem with 5F ROM.
Dip Switch 8 is ON. This will freeze the video on power up.
Very important: My one dip switch is ON at 8, the white pin is broken off and I struggle to move, I am cautious to push to hard, will I broke it further or broke the board if push to hard with a screw driver?



 
Regards
Francois du Toit

[johnmcallister]

If you can please post some pictures of what your board is doing or even a video of it booting up - turn the game off and then back on so that we can see what the screen is doing while it tried to run from the beginning.

High - means that the pin isn't pulsing or going low.  If you had a scope and you were probing that pin it would just show a straight line at the 5 volt level. 

Clock signal grounded would just mean that it wasn't pulsing and again if you were probing that pin it would just show a straight line at the 0 volt level or "ground".

The dip switch if it's working and #8 is on and your screen is freezing then yeah you need to somehow make it go off.  Maybe try to get a razor blade or a sharp object that you can really get a hold of the broken dip and move it the direction you want without a lot of downward pressure and more side to side force to make it move.

Short is when two pins are supposed to be separate, somehow are now touching or are connected somehow when they shouldn't be.  So if you have two boards and one is shorted and the other isn't you would be able to take your meter and put it on ohms and then measure on the good board between those two pins you would get a higher ohms reading (~1000 ohms or no reading at all "open") rather than a (0 ohms) shorted reading on the bad board.

[francoisadt]

Hi John

Thanks "AsteriodsMachine" for your answers. I will take a video tonight.