Game Boy DMG that is dead on batteries but works on the DC jack

The DC jack test tells you everything

Run the console on a known-good 6 V DC supply first. If the screen lights and the power LED comes on, the DC-DC converter board on the left side of the shell is producing its rails and the LCD is fine. Everything left is the battery path, which has four possible failure points and takes ten minutes to check.

The most common one is not corrosion but the jack itself. The DMG barrel jack has an internal leaf contact that opens when a plug is inserted and closes when it is removed. That leaf fatigues, and when it stops closing the batteries are permanently disconnected while the adapter still works.

Four measurements in the battery path

Work from the battery compartment outward. Write down the voltage at each stop, because the point where it drops to zero is your fault.

Corrosion on AA terminals from a leaking alkaline cell is the second most common cause. Leaked electrolyte travels along the metalwork and shows up as white crystalline deposits or as a dull grey film on the nickel plating.

1. Fit four fresh AAs and measure across the battery pack at the terminals. Expect 6.0 to 6.4 V open circuit.
2. Measure at the two solder pads where the battery wires meet the main board. A reading lower than the pack means the wires or the terminal rivets have resistance.
3. Measure at the input pin of the power board with the console switched on. Under load you should see at least 5.4 V. Below 4.5 V the console will not start.
4. With the adapter unplugged, measure continuity from the battery positive wire to the positive pin of the DC jack. Open circuit means the leaf contact has failed.
5. Inspect the four AA terminals and both springs under a bright light for white or grey deposits. A leaking cell leaves corrosion on the spring before it reaches anywhere else.

Cleaning the path or replacing the jack

Clean corroded terminals with white vinegar on a cotton swab, then rinse with isopropyl alcohol. The vinegar neutralises the potassium hydroxide from the leak; the alcohol removes it and stops the acid attack. If the plating has been eaten away, replace the terminal rather than trying to clean it, because a corroded terminal will keep building resistance.

For a failed DC jack leaf contact, replace the jack. The DMG jack is a through-hole part on the main board with three pins and it is one of the easier desolders on this console. Do not bend the leaf contact back into shape; it will work for a month and fail again, and a bent leaf can short the adapter input to the battery positive.

1. Clean the terminals and springs with white vinegar, then isopropyl alcohol. Let dry for ten minutes.
2. Check the battery wire solder joints for cold solder. Reflow them at 330 °C with a little fresh solder.
3. Replace the DC jack if the leaf contact is open with no plug inserted.
4. Fit a set of AAs and confirm 5.4 V or more at the power board input under load.
5. Test with a cartridge and let it run for ten minutes. A marginal contact will often drop out once the console warms up.