Neo Geo AES No Cartridge Reading Repair

A Neo Geo AES (NEO-0 PRO-POW-3) mailed in, the client states it’s getting difficult to read cartridge over the years and finally it gave up. Also there was a minor issue that RGB pixels scattered in the background. The client thought it might be VRAM, cartridge connector or BIOS related. He also provided some detailed pictures of apparently some rework done near the ROM and E0 chip.

Diagnosis

A non booting console with a socketed ROM and some rework has been done. The first thing to figure out is the rework. The ROM is quite easy to lift off makes me first to check the quality of the socket installation. All appears good.

Then inspect the continuity all the rework. They all appeared to be a mitigation work after a disaster which likely is an attempt to socket the ROM and make it replaceable. A lots of VIAs and traces are damaged so a later attempt to fix the trace applied.

Tested the continuity seems all working. Then the integrity check of the ROM.

The ROM dump came back cleanly.

Then only one way to find out, scope it.

Turns out there are two low address bits are having problems. They are not entirely off the address bus, but the tickling is weak, unable to register a proper HIGH. That is because the old rework solder joints became brittle and built up oxidation.

The repair

Rework those two bits, replaced the old wire with thin softer copper, then applied UV cured PCB protection for all reworked area.

The console boots fine now.

To fix the scattering noise issue is quite easy. The culprit is the unofficial 9V 1A adaptor, which apparently having trouble to power this 8W machine. Replace it with a better power adaptor fixed the problem.