Initial Power Up (Neo Geo AES)
One of the main issues with Neo Geo AES is their power rails.
The first version of the PCBs had no voltage regulation whatsoever and expected clean stable 5V power to come in to the system. The system had no reverse polarity protection so injecting 5V the wrong way would usually blow the VRAM on the system or other parts.
On top of that, later revisions incorporated a voltage regulator circuit and increased the input voltage to 9V from 5V, without changing the connector. This lead to many people using a power supply from a second generation AES in a first generation and totally destroying the board.
FInally, .... confirm inductors and noise etc...
Before doing anything at all, you must open up the console and determine which version you have.
The simplest way to find out if you want to use 5V or 9V in the system is to look down by the power switch.
You will either have a 3 pin PNP transistor (5V version), or a 5 pin voltage regulator (9V version).
Sometimes the 3 pin PNP transistor is higher up and green, usually glued to the board poorly.
To establish basic operation, we want to power up the console from the bench to monitor for current, and ideally use the RGB output through an OSSC converter as this gives us vital diagnostics information.
Ground is always the bottom pin as far as I have seen but it's easy to check which pad has continuity to the ground pin of the cartridge slot top left.
You can also trace which pin goes to the power switch; this will be the positive one.
Now we have established if the system is a 5V or 9V system, we can solder wires to the underside of the DC barrel and apply 5V or 9V from the bench power.
Limit your bench to 2 Amp current pull, connect up your RGB cable to the OSSC, and turn on the power switch.
You can also bypass the regulator and power from 5V directly over the ground and 5V pad of the diode on the 9V versions.
On a fully working console, you should see a current draw of around 1A on 5V systems, and about 0.5A on the 9V systems, without a game inserted.
The RGB video signal should lock in at 264-p, 15.58kHz, 59.04Hz or there about.
With no game and the default BIOS, you should get a solid blue screen with a slight black border.
If you do not get a blue screen, there are several places to start.
All the below things are highlighted in a single video here.
If you get a valid video signal, but the screen color is different, the power circuit is ok, move on to the Visual Diagnostics page.
Confirm your power draw and voltage haven't dropped, meaning you have severe under-voltage causing no signal.
If you have no power draw at all check your power switch, inductors, fuses and voltage regulators/transistors.
If you have correct power draw, correct voltage (5V direct or 5V after regulator), but still no video out, it could be many other things but your power circuit is likely ok.
If you see a slower than expected video output frequency, such as 14.74kHz, 56.06Hz, this is likely from under-voltage or lack of current capability of the power supply, or the power path / transistor / regulators cannot pass the required voltage/current.
Graphic glitches, specifically non-moving glitches (or in severe cases horizontal shifting lines), such as solid blocks of color usually at the top of the screen, ghosting fading down from the top of the screen, or overall blocked static graphics, is from slightly under-voltage systems.
Usually this is from around 0.1 to 0.4V drop under the expected 5V for the system.
This is typical when using flash cartridges that are power hungry, like the Neo SD Pro, or from a real dead/partial short in the system.
The Neo Geo AES has a self-resetting over-current circuit (I believe, not confirmed or reverse engineered yet but from a quick look it does).
The flash cartridge can take the current draw over the limit and cause the console to constantly reset.
I will work on a mod/fix to the current circuit to allow flash cartridges to work better when I get time.
An important step to confirm you have smooth voltage regulation especially on the 9V versions of the board with the regulator and diodes on is to set your oscilloscope to a slow time division (around 200ms) and observe the 5V rail.
If you have poor regulation like shown below, it can cause things like RGB or composite to not work, or failure to load from BIOS or game due to the interference on the rail.
IMPORTANT: Often poor quality bench power supplies will prevent the RGB output from working, and sometimes even composite.
Ideally use a CleanPower USB source, or original power supply when confirming video out.
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