Hi, I've finally taken ownership of a PAL Sega Mega CD 1. I got it cheap as it was listed online as 'not working', which it isn't. Here's what it's doing: It boots to BIOS screen but just displays the static picture, no moving text and no music. No lights are showing on the console either. The F1 fuse is fine as is a similar looking fuse on the main board. I have replaced all 10uf 16v caps on the main board too. Everything inside is hooked up correctly and I'm using the correct power supplies but still I can't progress any further than the static BIOS screen no matter what Mega Drive / Genesis I slide on above it. I have checked for damaged traces and can't find any. The caps on the main board had only minimal leakage. I've attached a photo showing the voltages I can find on the power board. They all read around 13v but stop on the left leg of the diode D1. Past this diode I can find no voltages on the power board. This test was done with the power board removed from the console and obviously no Mega Drive / Genesis attached. I'm hoping that this diode may be the issue but please let me know your opinion.
That looks correct to me - the diode is reverse connected and basically shorts out the supply when you plug it in backwards. So with a correct polarity supply you should be seeing 0V on the cathode and the supply on the anode as you are. If you go to the collector of TR4, it should have ~0V when the megadrive is switched off and go up to ~13V when it's switched on.
Static screen? That means that the cd drive isn’t working, make sure that some idiot didn’t forget to plug in the ribbon cable to the drive, then check the traces near that for damage. Also recap the board
Many thanks for the replies. After testing further with a Mega Drive attached it seems that it is not a power issue as the main board is getting a nice steady 5v. All ribbon connectors are seated firmly and have been tested for continuity. All capacitors on the main board have been replaced and test good for continuity. Still we have the same old problem of a frozen bios screen with the LEDs briefly flashing every so often once the Mega Drive is switched on. Only other thing I noticed is that upon accidently shorting a cap while testing I got a spark and the red LED flashed and the CD drive made a very brief noise as if the laser moved. I did notice that the ceramic red blob with 3 legs labelled EM1 on the main board has a lot of black gunk under it and the solder mask over traces by it was eaten away, however all these traces tested good for continuity. EM1 has continuity between the outer legs. Could EM1 be related to the lack of sound and animation on the bios screen? I believe EM1 may be a filter but I'm not certain. I can find no obvious broken traces.
Pics? I too have a board that I recapped that started to act this way. Nothing was wrong before I recapped it and it's doing the same thing. And its not my first one that I've recapped. No broken traces, no random solder balls on any chips (hot air was used to remove the old caps). Board is clean of all and any flux. Multiple Genesis consoles. New ribbon cables. Directly soldered bios so no seating issues. I've even re-flowed IC7 and IC8, the bios and we're at the same juncture lol. But pics help, maybe someone else will see something you don't. So post some lol it could help us both and others.
I was trying to fix a sega mega cd with the same fault I was looking at the service manual the sanyo ic does the cd-rom checks and the sega 315 chip does the same i would iike to do some digging how to find the fault. I used to buy broken mega cds a lot and had a stack of spares sadly no longer have part's.
