Tough Sega CD Repair Assistance Request

[SkydivinGirl]

Hey everyone!

I've been trying to repair a Sega CD V2 that wouldn't power on. When I opened the system, the fuse was blown and there were some scorched components in the power circuit. I've fixed all the power issues and I'm getting 5V on the main power rails and on the chips. Unfortunately, the system is still not turning on and I'm not getting any LED activity at all.

Here's what I've done:

1. Replace bad fuse.
2. Replace other bad power circuit components.
3. Re-capped entire board.
4. Checked entire board for cold solder joints.
5. Manually powered up the 5V rail with a jumper wire, bypassing the Genesis.

At this point, I'm not sure if a chip was fried but I'm not sure how to proceed with troubleshooting. I'd appreciate any thoughts you may have.

Thanks!

Heather

[Ziggy]

Hello, and welcome to Racketboy!

Just to get past some of the easier stuff...

Have you verified that the power adapter you are using for the Sega CD works?

Have you tried cleaning the Sega CD's edge connector (the one that mates up with the Genesis) as well as the Genesis' expansion slot pins? You can clean them just like any other cart/slot.

When you say it wont power on... You are power on the Genesis with the Sega CD attached, with no cart in the Genesis, and getting only a black screen?

[SkydivinGirl]

Thanks for the welcome and the reply! I use the power supply and Genesis that I use with my Sega CD. I know all this is good. I have cleaned the cartridge connector and it's good. I power on the Genesis, connected to the Sega CD, and just get a black screen. No lights on the power LED.

I've also hooked it up to my bench power supply and applied power to PIN 28 of the cartridge port to simulate powering on a Genesis. I'm getting 5V from the voltage regulator and at all the chips.

Thanks!

Heather

[Limewater]

I don't know much about the Sega CD, and the only schematics I could find online were half illegible, so I'm dubious to try to offer any advice.

However...

Based upon this schematic:
https://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:sega-cd-v2-funai-schematic-mega-cd-main-pcb.png

It looks like the main custom IC has to boot and Vcc2 has to be present for the power LED to come on.

Capacitor C306 looks like it's straight across Vcc2 and ground. What voltage are you reading across that capacitor when the unit is plugged in? I am not entirely sure at this point what Vcc2 should be, but it's likely supposed to be 5V.

Have you looked at the service manual (and supplement) here?
https://gamesx.com/wiki/doku.php?id=schematics:console_related_schematics

I'm guessing that your problem is going to be more involved than what is covered in a technician's manual, but you never know.

[SkydivinGirl]

Thanks for the reply! I'm fairly certain the main IC is burned out. I'm getting correct voltage at all the chips but it appears that it's not booting far enough to actually do anything.

I've looked at the schematics and service manuals but nearly all the troubleshooting in the service manual is in relation to the drive and doesn't go into details about the boot process on the main board. I could hook up the logic analyzer to see what's happening. I wouldn't know where to begin without a reference as to what I should be seeing as opposed to what I am seeing.

Thank you,

Heather

[Ziggy]

Oh, nice. I was about to ask what kind of equipment you have for testing.

I would say take a look at some ICs with the logic analyzer anyway, even if you don't know specifically what you're looking for. You can at least look for ANY activity. So if something is dead, that might point to a faulty part (or just possibly something at idle). You can also check to see if any of the ICs are getting excessively hot. You can tell well enough just by holding your finger on them, if it's just really warm or fry an egg hot. Or use one of those thermometer guns, you can get really cheap ones now. And they don't have to be super accurate, just ball park accurate so you know if an IC is shorting out and overheating, or in the range you would expect it to be.

[SkydivinGirl]

I've already done the 'hot to the touch' test on all the chips. Nothing is getting too hot. I may just re-flow some of the major chips to see if it helps. I'll hook the logic analyzer up to the chips that have documentation to see if they are doing anything. I'll let you know what I find.

Thank you,

Heather

[Ziggy]

I may just re-flow some of the major chips to see if it helps.

You might need magnification unless you have really good eyesight, but you can use a pick/probe to check each individual pin on all of the surface mounted chips to see if any of them can move (which means they need to be reflowed). Or just go ahead and reflow all of the chips, which would probably take the same amount of time as checking them.

[SkydivinGirl]

No worries there. I have a nice AmScope stereo microscope.

[Ziggy]

Nice!