PCB Repair Help - MikesArcade Pacman Repair Log Intepretation needed?

[francoisadt1]

Hi 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 coulours 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

[yotsuya]

Hi 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 coulours 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

Try a jewelers screwdriver on that broken dip switch. Try cleaning it with alcohol before you shift it. Since it’s already broken, I don’t think you can do any more damage.

[francoisadt1]

Thanks for answering my last question on the list about the broken DIP Switch switching over that is very stiff

[behrmr]

I tried to answer each question individually but the answers are mostly all the same.

You need to get a logic probe and learn how to use it on CMOS and TTL components.  There are many videos on YouTube of how to do this.

Your logic probe will tell you if it's High or Low.  Essentially high is 5v and low is 0v but you need a probe to safely test this.

Grounded or shorted mean the same thing.  E.g. the pin is shorted to ground.  Where he mentions this it is because it shouldn't be that way.  You need to use your probe to determine what is causing the short.  It could be the chip itself or it could be another faulty component in the same circuit.   You will also need the schematic so you can follow where the circuit goes.

There are many videos on YouTube that you need to seek out and find and use as a primer.  "TTL logic" and "How to use a logic probe" would be good starting search terms. 

You also need to be quite good at soldering and de-soldering because most chips on these are not socketed.  Pac-Man PCB's are not easy to work on.  The traces are very fragile and chips can be very difficult to remove.  If you don't have the right equipment you are just going to ruin the PCB.  Working ones are around $100-$125 plus shipping when you can find them.  Also maybe substituting a 60-in-1 set for single game is an option for you with an adapter.