Sega Game Gear scrambled graphics and white screen: tracing a broken video RAM line

This is the same Game Gear from our full recap case study. It left us tested and working, but about a week later the owner got in touch with a very detailed report. Most of their cartridges now gave a plain white screen with no sound. The two that did start showed badly scrambled graphics, with images overlapping and duplicating themselves, and the picture looked clearer at one particular position on the contrast wheel. There were also some intermittent shutdowns with a flashing red power light.

We asked for it back under our warranty so we could find out exactly what had changed.

Reproducing the fault

The first job was to prove whether the fault was in the console or the cartridges. On a bench power supply, with our own known-good test cartridge, it did the same thing: some power-ons gave a white screen, others booted with scrambled graphics. So the console itself had a fault.

Scrambled, overlapping graphics on a Game Gear usually point at the video side of the board: the video chip, its video RAM, or the connections between them. On this board revision the video chip sits on one side of the board and the video RAM sits on the other, so every connection between them passes through the board.

Reflowing the video RAM, the cartridge slot, the CPU, the work RAM and the LCD ribbon joints made no difference. That ruled out a simple dry joint and pointed at a break somewhere in the wiring between the chips.

Finding the broken line

We tested every pin of the video RAM in diode mode against ground. Pins that are properly connected all read about the same, because you are measuring through the protection diodes of every chip on that line. One pin stood out: pin 25, address line A8, read far higher than its neighbours.

With the console running, the oscilloscope confirmed it. Every other address line on the video RAM was busy switching, but A8 was completely flat. At the other end of the line, on the video chip, A8 was switching normally. The signal was leaving the video chip and never arriving at the RAM.

With one address line missing, the video RAM cannot tell two areas of memory apart, so graphics get written over each other. That is exactly the overlapping, duplicated picture the owner described.

The repair

• Fitted a fine bridge wire from the A8 output on the video chip side to pin 25 of the video RAM, restoring the missing connection.
• Checked the new wire for any bridge to the neighbouring pins.
• Confirmed on the oscilloscope that A8 now switches at the RAM.
• Power-cycled it repeatedly to make sure the fix held, because the original fault changed from one power-on to the next.

The first power-on after the repair: a clean, stable picture on our test cartridge.

The white screens were the cartridges

With the video fault fixed, our test cartridge ran perfectly, but the owner's Sonic 1 and Sonic 2 still would not start. After a thorough clean of their contacts, both booted and played normally.

A white screen with no sound on a Game Gear is very often the cartridge, not the console. A quick wipe of the outside contacts is not always enough, so cartridges that still will not start are worth opening up and cleaning properly with contact cleaner.

Sonic 1 running clean after its cartridge contacts were cleaned.

What about the flashing power light?

The flashing red light followed by a shutdown is the Game Gear's low-battery warning. It did not happen once on the bench supply. The console had come back with batteries fitted, so weak batteries are the likely cause. If it keeps happening on fresh batteries or a good 9V centre-negative supply, that is worth a closer look.

Result

The picture is clean again on every cartridge we tried, both Sonic games play properly, and the original Sega screen is still fitted. The repair was done free of charge under our warranty, with free return postage.

The volume wheel still crackles while it is being turned. That is wear inside the 30-year-old volume control, which cleaning cannot fix, so we offered the owner a replacement sound board as an optional extra rather than charging for it as part of the repair.

Got a Game Gear with scrambled graphics, a white screen or no picture at all? See our Game Gear and Game Boy recap service, or for board faults like this one, our soldering and board repair service.