Atari 5200:Bypassing the Switchbox (4-port)

By default, most 4-port Atari 5200 models have a single permanently attached RF video cable that also doubles as the power cable for the console. This configuration requires a special switchbox made specifically for the Atari 5200 which provides power and also provides the RF signal to a TV. The switchbox can be a point of failure, and the combining of power and audio/video into one wire can contribute to audio/video interference. In the later 2-port models and a handful of 4-port consoles, a dedicated power jack was added to the console, allowing these consoles to use a conventional manual switchbox.

Overview

In a normal 4-port 5200 console, the DC input power that travels through the RF/power cable is filtered out by an inductor labeled L8, which then supplies this DC power to the two 7805 voltage regulators. By removing L8 and injecting input voltage to where L8 connects to the rest of the power circuit, the switchbox can be completely bypassed.

Notes

• The included diode is for reverse-polarity protection and isn't necessary but is highly recommended.
• Removing the original 47 or 4700 µF filter capacitor is not necessary, but it can be replaced if desired.
• You do not need to remove the metal RF shielding for this mod, as all of the power circuitry is outside of the RF shielding.
• This kit uses the original power supply, though any 9–11.5V 2A DC power supply with center positive 5.5 mm outer diameter, 2.5 mm inner diameter plug will work. You may also substitute any power jack of your choosing, such as a 5.5 x 2.1 mm barrel jack wired for center negative polarity so a model 1 Sega Genesis AC adapter may be used.
• While the attached video cable can be removed, it is recommended to leave it intact in order to test the mod afterwards.

Materials and Tools

Materials

• Leaded solder
• 4-port power jack modification kit, available from Console5
  • If not using the kit, gather the following:
  • 5.5 x 2.5 mm panel mount DC power jack (can be substituted for power jack of your choosing if not using original PSU)
  • Hookup wire
  • 1N4001 diode or equivalent
  • 0.1 µF ceramic capacitor
  • 47 µF or 4700 µF 25V electrolytic capacitor (optional)

Tools

• Phillips head screwdriver
• Soldering iron
• Multimeter
• Flush cutters
• Wire stripper
• Multimeter
• Desoldering braid or desoldering gun (optional)

Procedure

1. Flip over the 5200 console and remove the seven screws securing the shell. Be mindful of the two rearmost screws near the controller storage area, which are shorter than the rest.
2. Carefully remove the top shell and set it aside.
3. Remove the motherboard from the bottom shell. Route the RF/power cable out of the bottom shell and secure it so it does not get in the way.
4. Snip out or desolder inductor L8, which is located right between the RF/power cable and the RF modulator.
   • Optionally, remove capacitor C45 and replace it with a capacitor of the same value. Depending on the motherboard, the footprint underneath it may be different and it may be a large (4700 µF) or small (47 µF) capacitor.
5. Locate an area to mount the power jack. It is recommended to place it close by the channel select switch, similar to a 2-port console.
   • Some 4-port consoles may have a large square hole near the switch, which is where the power jack on a 2-port console would normally be. This hole may be too large for most panel mount jacks, but a large washer or piece of plastic secured with epoxy behind the hole should be enough to provide extra support.
6. Drill a suitable size hole for the power jack and mount the jack to the shell.
7. Solder the cathode (striped end) of a 1N4001 diode to the lower (towards the front) via of inductor L8, then solder the anode to the red wire of one of the quick-release connectors included with the kit.
8. Solder the black wire of the same quick-release connector to a ground source. The rightmost lead of capacitor C36 or leftmost lead of capacitor C310 are good choices.
9. Solder a 0.1 µF ceramic capacitor between the center and outer posts of the DC power jack. Ensure that they are not shorted together.
10. Solder the other end of the red wire to the center post of the power jack, and the other end of the black wire to the outer post of the power jack.
    • If you wish to use a tip negative power supply such as a model 1 Genesis AC adapter, solder the red wire to the outer post of the jack and the black wire to the center post.
11. Reassemble the console to the point where it can be tested. Test the power mod by connecting the RF cable to a regular manual switchbox or coax adapter on your TV, then connect the power supply to the jack you just installed. If the console continues to power on and function normally, the test is complete and the console can be fully reassembled.
    • Optionally, the hardwired RF cable can be removed from the motherboard to make future repairs or modifications simpler. If you wish to retain RF output after removing the hardwired cable, a standard RCA cable can be connected to the RCA jack on the motherboard and then routed through the bottom shell.