Sega CD model 1 power problem.

So much fun on this thread ... So I took my MEGA-CD out of the box for some gaming fitness and guess what ? BLACK SCREEN...
Since I am not someone who would let this ruin my day, I decided to take the challenge of reviving it.

Board front, showing WORD RAM BANK chips, clock board, SUB-CPU and the four SUB-CPU RAM chips :


Board rear, showing SUB-CPU RAMs, SUB-CPU, BIOS EPROM, CD decoder and it's RAMs, PCM chip and it's PSRAM memory:


Trace I had to patch on the under side: (three pads shorted with a piece of wire)

This trace was cut by corrosion and it removed the connection from the pin 1 of the four RAM chips for the SUB-CPU (/OE or output enable).
The fault made so the RAM chips could be written to but not read, causing the SUB-CPU to be unable to start.

That caused the unit to fail starting, with a blank screen on the screen and no front leds lit. Exactly as you describe on your faulty unit.
Keep in mind that any trace that is broken and prevent the RAM from being written *and* read properly will have the exact same effect.

This is a early MEGA-CD unit so it has a "patch chip" on the connection board to fix an errata at the clock circuit of the 208 pin ASIC.

The board soldered to the 4-pin crystal place in the main board has a 74LS74 to divide the clock which is sent to the connection board "patch chip".

 

That board looks really weird due to that patch chip. BTW nice paw print on that secondary BIOS chip.

 

http://www.tigre.com.br/pt/index.php That company makes the insulating tape I used there. Their name "tiger" and the paw is their logo lol...

 

Bad_ad84 currently isn't doing any modding or repairing, do you know any one else that might be able to help me on my side of the world. Or should I look for someone in the user market place?

 

If I weren't on the other side of the Atlantic and my country weren't such a horrible place to send things to I would be more than happy to help you with these.

 

You do get all the best prices in the steam sale though!

 

Yea, I've heard that shipping to Brazil is hell. Lots of packages don't arrive or are sluggish at best and the receiver gets slammed with custom fees and duty.

@Bad_Ad84: I'm well aware!

 

If all else fails and you want to ship it state side I could take a look. Won't be cheap.

 

Thanks for the offer, but just from shipping it state side and back it might be ending up cheaper to buy a new one.

BTW could someone mark the place where the corroded trace might be? As, at least in real life, doesn't look damaged.

 

lol corrosion are random damage. I could inspect the board in person and find it easily or not depending on where it is. The point of using a continuity meter is test the traces you cannot see (that particular board has ink and copper coating on top of the logic traces so it does not need a metal cage to prevent radio frequency emissions.

The Export model (USA SEGA-CD or PAL MEGA-CD) is the inverse, the power and ground lines are close to the center of the sandwich that composes the board and the traces are exposed outside, quite visible. A lot easier to repair.

Sorry if you cannot find the corrosion yourself you will need to send it to someone who knows about these repairs.

 

You're going to either have to sit there and test every trace you can see or send it off to someone else. There are no shortcuts in this game.

 

No I'm aware, what I meant was if someone could mark the general facility of the corrosion. Basically trace the +-border of corrosion so I could check the trace in that area.

 

basically anywhere the nasty leaky cap stuff was / is / could have been.

 

as APE said you need to sit there and check one by one

a very primitive not 100% accurate way is to shine a bright LED light behind the board and look for any broken traces, this wont work where ICs are

 

When I was diagnosing my board, I used the service manual and these schematics:

http://console5.com/techwiki/images/f/fe/PC_BD_MEGA-CD_MAIN_BD_171-8105C-Schematic-1_of_4.png
http://console5.com/techwiki/images/c/cd/PC_BD_MEGA-CD_MAIN_BD_171-8105C-Schematic-2_of_4.png

To trace the tracks going from the 512KB RAM bank to the SEGA/Fujitsu ASIC and the 68HC00012 CPU. That was how I found the broken trace. It's broken point was not visible at all. I had to follow the schematic to find which one was broken and certainly one is enough to stop it from working.

 

I've got two spare power boards. Any chance you know what is broken or what you need.

EDIT: Sorry just saw that you replaced your power board. I do have a spare disk drive that is sony though

 

Hey,

Sorry to revive a (semi) dead thread but I have a similar problem to the OP.

I bought a model 1 Mega CD as untested hence the price a few years ago. When I powered it up there was nothing. A quick google search pointed to the fuse which I checked ad confirmed was fried but after replacing and trying again, still nothing.

I checked the fuse again which had blown. So I decided to by-pass the fuse to see what happened. The 7805 got REAL hot REAL quick and there was smoke coming from the general area. I've had a peek around for any obvious shorts but can't see anything.

Has anyone had a similar fault like this or know of any other checks I can do before slinging it in the bin?

Regards,