TUT: How to DC mod a PAC-MAN PCB

[silverfox0786]

I have been looking into DC modding my Midway PAC-MAN PCB. I started with looking at the Galaxian write up that was written by Paul Swan and currently resides over at Macros Website.
http://www.arcades.plus.com/galjamm2.htm
From there is started reading up on Diode Rectifiers and how they work to convert AC - DC. I find learning how a circuit works makes for better modding rather than just doing what someone has outlines for you.

I want anyone reading this to understand the process and what they are doing rather than me just tell them how to do and they do it, not knowing what they just done.

So here goes in a nutshell.

An AC current (Alternating current) is a current that will raise and lower in an equal current above and below the neutral point (0Volts)
So a 7.5V AC would rise to +7.5V and drop to -7.5V with 0V being its mid-point.

An AC input with and inline Diode with remove the lower portion of the AC current. Leaving you with a rippled output. +7.5VPeak and 0V.
This is called a Pulsating DC. Also known as a Half Wave Rectification.

When adding an Electrolytic Capacitor to the output and Neutral of the circuit, you essentially clean up that pulse (known as a Smoothing Capacitor) this is known as reducing the Ripple

Armed with knowledge we can deduce that when the 7.5V AC goes in and hits the Diode it will become a Pulsating DC Voltage, so at this point we know we have done half the work to getting DC and then with the addition of the Electrolytic Capacitor we then complete the conversion to DC

So The Galaxian mod looks like that is exactly what was performed. The Rectifiers have been removed. To allow for DC voltages to be used from the onset

Although bear in mind it’s not quite that simple and a lot of other things need doing to complete this Modification.

So now we start with The Galaxian Mod as our starting point and look at what was performed. This will not only help us understand better the process but also verify weather what we are thinking is right or wrong

Replace D4 (A15F diode) with a wire link
Replace D5 (A15F diode) with a wire link
Replace D6 (A14F diode) with a wire link
Replace D7 (A14F diode) with a wire link

So the Diodes above are the Rectifiers and because we want to send in a DC current already we don’t need them anymore. But we do want the circuit to carry on and not break, so we wire link them.

Now for the Electrolytic Capacitors that are part and parcel of the rectification circuit. Well those where and still are Smoothing capacitors so they can stay to now act as DC smoothing capacitors.

The next thing we look at is

Remove IR2 (78GU I.C.)

This item is a Adjustable Regulator, which again is not needed anymore as we will be giving the PCB the correct DC voltages of 5V DC and 12V DC. With that will come this resistor.

Remove R88 (50Ohm 5W resistor)

As again this is part of the regulator circuit. It drops the voltage to give the correct input voltage so the correct output voltage can be obtained, and can be removed also.

We also look at the Transistor

Remove IR1 (D44VM4 transistor)

This transistors function is to compliment and attenuate the output voltage from the regulator so again it is not needed as the Regulator has been removed

The last part to be mentioned is the Resistor

Replace R87 (4Ohm 10W resistor) with a wire link

This Resister is there to drop the converted 7.5V DC down to 5V DC. Because we are now using the correct 5V DC input voltage this can now be removed and the circuit patched with a wire link. It’s important to remove this resistor or we will get a DC voltage drop on the circuit because of it.

2 items not mentioned that I found in the Schematics are C35 and C36

C35 is a Tantalum Cap on the Regulators input and GND, I seems this is for attenuation and is not needed again as the Regulator has been removed. Leaving it in won’t harm the circuit. I just won’t be connected to anything.

C36 again is a Ceramic Cap which looks like a Smoothing cap in-between the Regulator output and the Base of the transistor. Same applies to this as C35

Now that we have dissected the Galaxian AC to DC mod we can look at the PAC-MAN PCB as they share a similar setup and are made by the same Company Midway.
Here is the Schematics for both

As we can see from this the PAC-MAN schematics is the Top one and the Galaxian one is bellow and they both share the same parts and Circuit layout.

So I have isolated the parts and concluded where and how the DC mod needs to be done

Components in RED need to be removed. Components in Yellow Stay but where originally part of the AC circuit. Components in Pink Optional Removal. Components in Purple Remove if present. Green Lines are Wire Links.

And as per bellow

PAC-MAN DC Mod

Remove IR1 (78GU I.C.) Galaxian IR2
Remove (D44VM4 transistor) Galaxian IR1
Remove R52 (50Ohm 5W resistor) Galaxian R88
Replace D6 (A15 diode) with a wire link Galaxian D4
Replace D7 (A15 diode) with a wire link Galaxian D5
Replace D3 (1N4004 diode) with a wire link Galaxian D6
Replace D4 (1N4004 diode) with a wire link Galaxian D7
Replace R53 (4Ohm 10W resistor) with a wire link Galaxian R87
Optional Remove C6 (0.1uF Ceramic) Galaxian C35
Optional Remove C5 (10uF Tantalum) Galaxian C36

Enjoy Guys
Silverfox0786

This can be posted anywhere you like but please give me credit for the write up.
silverfox07862015-03-04 00:25:09

 

[u72]

Nice Tut!

 

[silverfox0786]

Nice Tut!

#

Thanks Andy, but im more amazed at how you managed to read that whole tutorial in less than a min. HEHE

 

[cmonkey]

Haven't you ever seen the movie Short Circuit where Johnny 5 reads entire books in a couple of seconds.....

Nice tutorial there Sarj

 

[RaveN]

Why are you removing the regulator, transistor and associated resistor Sarj?

 

[Equites]

I usually just bypass the 4 diodes because I'm lazy and like to keep the PCB as original as possible so it can easily be converted back to AC.

 

[silverfox0786]

Why are you removing the regulator, transistor and associated resistor Sarj?

because they don't have any function after the removal of the Diodes

no point having them sitting there doing nothing

unless you take on Nads reasons and want to mod back to AC then yeah leave them on so its less components removed and less components put back on

 

[Jodo]

Nice work but please can you provide a direct link to Paul Swan's work in your introduction; I think it's only fair

 

[silverfox0786]

Nice work but please can you provide a direct link to Paul Swan's work in your introduction; I think it's only fair <span style="line-height: 16.7999992370605px; : rgb237, 246, 255;"]

</span]

link added

 

[RaveN]

I do the same as Nad.
You can convert to DC with minimal wire jumpers (it looks like you can get away with just 3 as a bare minimum).
The beauty of that mod is it's quick and easy, you preserve all the other components and therefore it's easy to convert back.
If you remove all of the red parts, you don't gain anything from it, you'll just be creating more work for yourself, and it makes it a great deal harder for people to convert it back in the future (a lot of the boards will probably out live us!)

 

[guddler]

http://www.jammaboards.com/store/pacman-ms-pacman-pcb-to-jamma-cabinet-adapter-pacman2jamma.html

 

[Equites]

http://www.jammaboards.com/store/pacman-ms-pacman-pcb-to-jamma-cabinet-adapter-pacman2jamma.html

Martin - Thats just a JAMMA adaptor, but PCB still needs to be converted to work via DC. Having said that, I've had good success getting AC Pac's to work on DC without modification or cranking up the volts. Galaxian, Moon Cresta etc I've had less success with for some reason.

Here is a JAMMA adaptor with the correct rectification for playing JAMMA PCBs in an original AC Pac Cab;

Equites2015-03-04 10:30:33

 

[guddler]

Point is, you can just connect the board to a jamma harness with the straight adapter and it works. I've never done anything more fancy than that. The DC voltage drops a bit, but not to a level where it doesn't work. Admittedly you might want something a little more permanent if you had a cab with a board living in it permanently but I've never had that and never will.
guddler2015-03-04 10:39:59

 

[Equites]

Point is, you can just connect the board to a jamma harness with the straight adapter and it works. I've never done anything more fancy than that. The DC voltage drops a bit, but not to a level where it doesn't work. Admittedly you might want something a little more permanent if you had a cab with a board living in it permanently but I've never had that and never will.

I've always found the same as said above, Pac will still work without mod.

 

[RaveN]

I've never seen that adapter before.
It looks like it has a boost DC-DC converter on it, does it boost the 5v up a tad to counteract the diode forward voltage drop?

 

[Equites]

I've never seen that adapter before.
It looks like it has a boost DC-DC converter on it, does it boost the 5v up a tad to counteract the diode forward voltage drop?

Yeah I'm sure that is what it does. No longer manufactured unfortunately.

 

[silverfox0786]

I made this tutorial as a help. last time I do that. seems more people are complaining about it then appreciating the effort

if you really wanted to be on a flip side and not remove anything then just solder to the 5V and 12V plain on the top of the board

 

[RaveN]

Not complaining Sarj, any tutorial/mod has to be open for discussion with constructive criticism, as it will be in the public domain.
People will appreciate your efforts and the explanation of how the AC section works.

 

[silverfox0786]

my main reason for doing this knowing all the other mods out there is because I searched high and low to find information and nothing is out there

so I learnt the info and decided to share it

it was meant as another resource to the already numerous methods people use

 

[RaveN]

yes, and that's appreciated.
It's informative and correct, we haven't torn it apart or anything.
The thing about this hobby is that everything should be done with preservation in mind. So it had to be mentioned here, otherwise you might have a ton of people stumble upon this tutorial and we end up with a load of Pac/Galaxian boards out there looking like bootleg boards, never to be used in AC cabs again.