The adventures of a Bartop Arcade v 1.0

43 Pages·2012·2.76 MB·English

The adventures of a Bartop
Arcade v 1.0

Projecting, assembling and hacking as a children back
in the 80’s
By Andrea Mancini

The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
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The jamma cable 2
The Pandora’s Box 5
The VGA plug 10
Mega HACK!!! 10
Power supply 13
Sound System 15
The THD 16
Short Circuit Protection 17
Thermal Shutdown 17
Build the cabinet 19
Electrical part 25
How to cut the Plexiglas 26
Electric system 29
Plug the world! 31
External power plug 33
The Autofire 36
Conclusion 39
References 40
Authenticity 42

Introduction

When I thought to build an arcade I supposed that would have been easy, but a plug
and play hardware wasn’t a paradise as expected to be… In this guide I’ll teach you
the basics about the hardware and some tricks to make your life easier.
We will talk about the “jamma cable”. This cable was the old standard used to wire
the motherboard to the peripherals (joystick, speakers…). You’ll learn some
hardware stuff but not so much about cabinet assembly….. I prefer teach you some
hacks more than how to be the perfect carpenter, because I’m not.
The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
Attribution-ShareAlike 4.0 International License.
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The jamma cable

The jamma plug of the Pandora’s box (the brain of my Arcade) doesn’t have test,
service, tilt and key slot pins. In the old circuit boards, test button if grounded active
the ROM integrity check. Service button was used to enter inside the configuration
menu. The tilt pin was used to check if the player was cheating by moving the
machine. The key slot is a plastic piece to avoid reverse connection….. Fortunately
my Pandora rocky version has the protection on board…. I heard about smoke and
flames on the old boards. These pins are not needed in newer Arcade because the
Pandora has a small button on the box that allow you to enter in the software setting.
Here you can see the differences between the classic jamma cable and the
Pandora’s one

The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
Attribution-ShareAlike 4.0 International License.
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Pandora’s jamma

The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
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Classic jamma

The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
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The Pandora’s Box

Let’s talk about Pandora’s….
This magic… almost …. box is a plug and play hardware useful to make a brand new
Arcade or to repair an old one.
You can find two version of Pandora’s Box : the HD version and the normal one. HD
version use only vga port. If you look at the circuit tracks on the board you see that
video data signal pins of jamma plug are disconnected (don’t trust vendors that
affirm that HD version has also video out on jamma). I’m not so expert about jamma
because I need to build an arcade with an LCD…. Well also a jamma cable is not
needed …. I was swimming in a mess of wire when I realized that an USB adapter
and 4 cables instead of 6 buttons x 2 + 4 joystick switches x 2 + 2 start buttons + 1
ground wire = 23 wires would has been a better solution.
I bought the Pandora “rocky version”…. The cheapest one…. It is a good device with
some expedients.
The Pandora, as I mention before, is “supposed” to be retro compatible with jamma
cables. I told supposed because the female plug in the box is not really a jamma
plug. I think due to patent protection, some pins in the Pandora’s jamma aren’t in the
right position. This is not a problem: if you want to keep back on life your old 80’s
baby just buy an adapter like this

http://www.arcade-projects.com/forums/index.php?thread/208-jnx-atlas-adapter-for-y
our-pandora-s-box-blue-elf-game-elf-etc/

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Fortunately I do not need to keep alive an old buddy but build a young baby.
Pandora’s box is not so bad but need some hacks to work fine. Before explain how
to hack it and boast myself :) I want to explain a little bit how the hardware works.
Ok, now deep inside the circuits!
This is a Pandora’s box rocky version as you can see in the picture.

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Is much cheaper that the classic version. The rocky cost about 32 EUR and the
classic one about 70 EUR… Big difference!!!! Here you can see a picture of the
classic version.

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The box change a little bit. Don’t care too much about the shape but look at the
name “rocky” engraved on the plastic shield. I think that the most important
differences between the two boxes are the lack of the jack 3.5 inch plug and the
encrypted software in the rocky version. Ok… what does it means? If you look at the
rocky board you see the housing for the smd jack plug but there is no plug.

Just solder it on the board and TATA!!! Now is a classic box. Unfortunately life is
hard….. The biggest problem is the code. If you take a look inside the sd card you
see some files. All this stuff is supposed to be a dedicated linux system with a game
emulator and roms. If you try to reverse engineering these files (you can use
different hex editor like HxD, Ida Pro…..) you can see that the code is encrypted.
This make impossible to understand where the roms are saved and is really hard
make changes (open source RULES!).
Here
http://mengxipeng.blog.com/2015/08/07/how-to-change-or-add-games-in-pandoras-b
ox-v3 you can find a good reverse engineering for the Pandora’s box classic version
and add roms. REMEMBER TO BACKUP THE SD CARD BEFORE DO IT! I mean
The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
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DUMP the memory and don’t do a copy and paste. This sd is formatted as boot disk.
I didn’t reverse the code because I solved some working issues by looking at the
hardware. Later you will see :)
Now give a look to the motherboard.

Here some specs:

- jamma plug
- Allwinner CPU
- RAM memory
- 12V to 5V stepdown (whaat???.... jamma pins waste)
- ATMEGA chip (probably used to control buttons)

By giving a fast look this make me remember a smartphone or a raspberry PI. We
have a cheap Android phone CPU with RAM, a stepdown (a circuit that lower the
voltage by using a PWM https://en.wikipedia.org/wiki/Buck_converter) and an
ATMEGA chip used by Arduino or other microcontrollers. You can see how the
retrocompatibility of the Pandora is only a waste of pins. You can notice that there is
no track on the board attached to the 5V jamma pin. It is not needed. So why use a
jamma???? (I think I’ll repeat many time this).
The Adventures of a Bartop Arcade v 1.0 by Andrea Mancini is licensed under a Creative Commons
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