Aquarius

composite video adapter v1.1 - DIY Edition

Support our site! Visit our favorite PCB manufacturer, $2 JLCPCB!

Abstract:

The Aquarius Composite Video Adapter Board is an after-market upgrade to the stock Aquarius that replaces the original RF modulator with a DIY solution using through hole parts and an inexpensive PCB. The adapter works with either PAL or NTSC systems!

Background

When I got back into the Aquarius in the Summer of 2019, I got a bare bones Aquarius that didn't even have the switch box or cable plug for RF output. I had to hack together a BNC cable with an RCA cable to even see the output to make sure the machine worked. It was frustrating, so I began researching the raw VID (composite) signal coming off of the video chip (TEA1002) of the Aquarius. I hooked a standard composite cable up to it but found the signal was too weak to be useful. I then found a video showing one user's success at adding an inexpensive video op-amplifier, and set about trying to find a similar chip in a more manageable PDIP-8 package that most users could more easily solder. I settled on the AD812ANZ Video Amplifier chip. Included in the chip's documentation was a sample single-supply (+5v) circuit, so I assembled the parts, bread-boarded it, and hooked it up. It worked on the first try. I then found the SND lead and discovered that it didn't need to be amplified, so I passed it straight through to the right and left audio out. After that success, I went through two PCB prototypes and settled on a design that fit within the stock RF modulator's form factor.

Purchasing

The Aquarius Composite Video Adapter Board is available at:

In addition, you'll need to get the components necessary to build the board, listed in the BOM (Bill of Materials) below. Note that there are both US and UK/EU tabs for the BOM.

AD812.pdf

Development Details

While I would LOVE to claim to be an electronics genius (not even close!), I relied on the support of friends and colleagues in developing this board. First, the composite amp circuit is taken DIRECTLY from the spec sheet of the AD812 video amp chip used to boost the signal. I wanted this board to be DIY, so I focused on THROUGH-HOLE components. And the circuit I used is identical to the one on page 16 of this PDF (Figure 53. Biasing for Single Supply Operation)...

The only real "magic" I performed was in taking detailed measurements of what the size and shape of the PCB would be so that it could be a drop-in replacement for the stock RF modulator. I also figured out a way to use a more standard 1/8"/3mm AV cable, and make sure that it centers itself in the TV port on the back of the Aquarius. But truth be told, anyone with a bit of electronics hobbyist experience could have done this as well.

Aquarius Composite Video Adapter - BOM

Build Instructions

Here are videos of the process of installing the Aquarius Composite Video Adapter board...

1. motherboard removal

First, you have to remove the Aquarius motherboard from it's case.

2. RF Shield removal

Next, you need to remove the RF shield that encases the motherboard.

3. RF Modulator removal

Next, removal of the stock RF modulator is necessary.

This video also shows removal of the 7805 power regulator so it can be replaced with a modern equivalent, which is optional (but a good idea).

4. Building the Adapter Board

Next, you need to build the Aquarius Composite Video Adapter board with the blank PCB and parts.

5. installing the adapter board

Next, you need to install the completed Aquarius Composite Video Adapter board in the Aquarius.

6. testing the install

Finally, you need to test your installation.

OPTIONAL: 7805 Replacement

Instructions on installing an OKI-78SR-5/1.5-W36H-C replacement for the 7805. Do this after Step 3, above.

optional: replacing the capacitors

Instructions on replacing the electrolytic capacitors on the Aquarius. Do this after Step 3, above.

More details on our Aquarius Capacitor Replacement page.

Troubleshooting

  • No video signal - Not all 3.5mm / 1/8" AV cables are wired the same. Check the image to the left to verify the pinouts for the cable you're using.

    • The BOM links to an Amazon part that SHOULD work, but some users have found that the RED and YELLOW plugs must be swapped.

    • If you want to bypass the cable and test directly with a hacked RCA video cable, solder/clip the video positive signal (center) to the left side of the 75 ohm resistor (second from bottom, R5), and the ground (outer) to any of the mounting point pins at the top, right, bottom, or left of the board. If you still get no signal, check your work and soldering.

  • Still in development - The circuitry on the CVA is fairly simple, so there's little that can go wrong. As we find quirks or problems, I'll post them here.