Fixing a Sega Nomad that won't run on batteries

I was recently lucky enough to pick up a new Sega Nomad, but unfortunately it didn’t come with a battery pack. I was excited to find a “3D Printed Rechargeable USB-C battery pack” on eBay and put in some nice quality 18650 batteries with plenty of juice, but the pack didn’t work!

Battery pack

It worked via the AC adapter but would not power on with the battery pack. This Nomad had been screen modded by someone else before I got it. The battery pack was fine, and there was voltage at the ribbon cable to the screen side. With the adapter it worked. With batteries, nothing.

The pin 26 and 28 bodge

I found a post from someone with the same issue in this thread on Sega-16. It suggests bridging pins 26 and 28 on the front board’s ribbon connector. Note that the pin numbers zig-zag between the two rows, so count carefully.

I tried it and it worked! However, nobody in the thread explained why it worked, and I didn’t want to leave a solder bridge in there without knowing what it was doing.

Tracking it down

Using a multimeter in continuity mode, I found that pins 26 and 28 were not connected. Pin 26 went to the outer contact of the DC jack. Pin 28 went to a joint near the power circuitry.

My first thought was the screen mod. The black wire for the new screen was soldered to the same pad as pin 26. If that wasn’t a proper ground on battery, it would explain the fault. I found another LCD install guide that used a different ground point and moved the wire there. It made no difference, so the screen mod was not the problem.

The power section of the front board, with the screen mod's black wire on the pin 26 pad

Next I looked at the jack. This leadedsolder Nomad repair explains that the jack’s third pin switches between battery and adapter power. With no plug in, an internal contact connects the batteries. When a plug goes in, the contact opens, so the batteries and the adapter are never connected at the same time.

You can’t see this switch by looking into the jack. It sits behind the outer contact. The jack has three legs, so I tested continuity between each pair, with and without a plug. On a working jack, one pair connects when there is no plug and disconnects when there is one. On mine, no pair connected at all. The switch was stuck open!

Why bridging 26 and 28 works

Pins 26 and 28 are either side of that switch. Bridging them does the switch’s job, so the batteries are connected again. On AC the switch is not needed, which is why the fault only happens on batteries.

Without the switch, either the AC adapter or batteries will work, but not both. Batteries should not be used at the same time as the power adapter because they could overcharge or damage the Nomad. Therefore, this was not a good solution.

The actual fix

The cause was a worn DC jack. I didn’t have a spare jack, so I tried cleaning it first:

Adapter unplugged from the mains, battery pack off.
Spray a little contact cleaner into the jack.
Push the adapter plug in and out a few times to work the cleaner into the contacts.
Let it dry before powering up.

Eventually pins 26 and 28 showed continuity with no plug inserted, which is correct. I removed the bridge, put the batteries in, and the Nomad powered on. Phew!

Unfortunately it didn’t last. The fault came back, and the Nomad would only power on if I wobbled the plug. Cleaning helps if the contact is dirty, but mine was worn.

Finding a replacement was difficult. It has to be a three-pin jack, because the third pin is the battery switch. The only compatible part I found was a DC jack for the PS1 and PS2 slim. It’s almost identical to the original.

The old Nomad jack (left) and the PS1/PS2 slim replacement (right)