Another Mega-Tech on the bench for repair, this must be about the sixth one I've worked on. They are always filthy so the first thing I had to do was clean it. The sockets also all needed to be replaced too like in previous Mega-Tech repairs.
When powered on I got nothing on screen and one of the Sony CXD1095Q chips was getting super hot. Replacing the Sony CXD1095Q with a nice new old stock one it powered up and worked on first power up displaying the cartridge list but on the second power up it was having trouble seeing the cartridges and only loading games from certain slots. The other CXD1095Q failed so I replaced that one too, this fixed the slots and loading issues.
With the 74LS125 socketed and replaced there was still no sync output. Sadly the 125 killed the sync pin on the custom 5313 chip when it failed. Fortunately I have a Mega Drive console that I've used for parts already as it had a broken case and the 5313A chip is still on there. The A version is a later version but is pin compatible.
Replacement 315-5313A fitted and I get a sync signal and a good image, the only remaining issue is I noticed on the all white Sega logo screen in Sonic the white was a little green looking. This again is a common issue with these boards where the transistors on the video output aren't equal, they all test fine but the only way to get a really balanced image (without adjusting the monitor) is to replace all three transistors with new ones, so that's what I did.
