Sega Mega CD Model 1 Bios Freezzing......HELP!!!

[Segarulz123]

Hi all. I have received a model 1 pal mega cd that appears to power on and when the image of the earth appears on screen it freezes. Doesnt boot any further and no lights on the front panel. How would I go about fixing this? Replace caps? Its not a fuse issue as it does output an image on the screen. No sound either. Help greatly appreciated.

[Segarulz123]

I have checked the fuse for continuity and thats fine. I notice the red access l.e.d flashes briefly on power up then nothing and we are then stuck with just the earth on the screen. No sound etc and console appears to be dead.

I am going to try a complete capacitor change on all boards in the console.

[Tokimemofan]

Usually that means that the CD-ROM drive ribbon cable is damaged or disconnected, Check that first. If it is running that far the Power/Audio Mixer board is working. The Drive board should be checked, the bios loads the background and then checks the drive before starting the music and the Sega logo. If it fails to access the drive the bios hangs with only the background loaded. There is another possibility, I have noticed that the 315 5548 ASIC on the motherboard often has failed solder joints, usually on pins 105-110. Start with the former, the ASIC problem usually causes a completely dead unit, for reference the 315 5548 is the large square IC near the LEDs, pins 105-110 are the ones closest to the save battery.

Edit: This is based on a NTSC-U/C unit, the PAL bios probably behaves the same way.

[Segarulz123]

Interesting. Many thanks for your reply. Indeed the background image loads then nothing so it seems from what you say an issue with the drive as I did buy this unit on ebay sold as "not recognising discs.......", only to find this issue when I turned it on myself. I may try swapping the drive from a working unit then to see if that makes a difference.

I was going down the recap route as I heard faulty caps can cause power issues but from what you say I dont think this is. Again thanks for the reply and I will make a new drive cable, replace laser etc first.

[Segarulz123]

Well I took the power board out and swapped it with my working one, still freezes. I then swapped out the cd-rom and same thing. Also put them in my other working one and it still works. So now I conclude it must be an issue on the main motherboard. So I am going to put that in my working mega cd and hopefully that will confirm where to start this repair....

[Segarulz123]

Right I can now confirm that for me the issue with the screen freezing when you boot the mega cd before the bios intro music is indeed a fault on the motherboard. I put the mobo from the faulty console into my working mega cd and bingo......same issue. So now I will replace all capacitors and reflow the board for cold solder points. Hopefully in an hours time I shall have revived this lovely creature.

[ProjectCamaro]

Right I can now confirm that for me the issue with the screen freezing when you boot the mega cd before the bios intro music is indeed a fault on the motherboard. I put the mobo from the faulty console into my working mega cd and bingo......same issue. So now I will replace all capacitors and reflow the board for cold solder points. Hopefully in an hours time I shall have revived this lovely creature.

Good luck!

[Segarulz123]

Right I have replaced the capacitors 41-52 on the main board but still it wont boot I am wondering if its the bios chip now.......this isnt looking good. Any experienced repairers on here ever come across this issue before?

[recorderdude]

I had the exact same issue with my model 1 a while back. There's a ribbon cable that connects the Drive to the actual SCD hardware inside the case that comes loose pretty easily, but I was able to snap it back on, and get a normal bootup after that.

...unfortunately, I was so excited about it that I manually closed the disc drive as I was reassembling it, quite possibly leading to the all-too-common constantly ejecting drive issue, so I swapped one issue for another :P

[Segarulz123]

Thanks for the response but I have checked that. Its definitely a fault on the main motherboard as I replaced it with one from another working machine and bingo all ok.

[Segarulz123]

Well I concede defeat on this occasion. I have recapped the main mobo. I have reflowed all chips on the main mobo. I have a fully working power and sound board as well as a cd drive. The cables are undamaged and all in place. I see no reason why this wont boot!!!!! I am giving up unless I can track down a replacement motherboard this one will be going on the spares pile

Thanks for the help guys.

[Tokimemofan]

Well I concede defeat on this occasion. I have recapped the main mobo. I have reflowed all chips on the main mobo. I have a fully working power and sound board as well as a cd drive. The cables are undamaged and all in place. I see no reason why this wont boot!!!!! I am giving up unless I can track down a replacement motherboard this one will be going on the spares pile

Thanks for the help guys.

Good luck I need one too. Inspect the ICs for slightly bent pins before giving up, the solder joints on these are rather dry so they break easily, 2 out of 3 units I have worked on have had problems on the ASIC I mentioned earlier.

[Segarulz123]

Will do mate thanks again.

[raylydiard]

Sega service manual tells me to check the reset line on the CPU.
i have two mega cd consoles that try to load but don't the drives tests work on a good console.
so its the sanyo lc89515 has a timing for the CD-ROM and tells the bios to boot.
but can sometimes be a CPU problem.

No joke i have a stack of faulty boards i will fix or get someone to check them out for me once the faults are found a chips replaced and boots that would be a break though.