Dead Sega CD model 1?

[NES-Luke]

I recently got a model 1 Sega CD, and I can't seem to get it to do anything.

On occasion when I flick on the Genesis connected to it, the lights come on for a fraction of a second, and the turn off again, and I sit there staring at a black screen.

Any ideas?

I've pulled it all apart and the cable going from the CPU board to the power/output board at the back seems to be bent at a pretty sharp angle. if that's dead, does anyone know the pinout for that cable so I could fashion my own replacement cable?

[Aidan]

Tough call when you have a multiprocessor system and it doesn't work!

Check power lines first. If there's any issues with power, then it isn't going to work right.

I have a working MegaCD at home, so when I get back from this work trip, I might be able to provide some assistance.

[NES-Luke]

I should also note that I don't have the grounding plate, but have tried to complete that circuit.

is it possible that it just wasn't a solid enough connection?

[kendrick]

The ground plate is more for shielding than anything else, since the expansion connector also completes the circuit and creates a common ground between the two machines. The lack of a plate won't significantly affect the operation of the Sega CD, and it certainly by itself wouldn't be the cause of the behavior you're describing.

Let's cover all our bases before Aidan's trip is over. Are you connecting a Genesis Model 1 or Model 2? If it's a Model 1 Genesis, do you have the stereo mixing cable present or absent? Also, have you verified that the power supply connected to the Sega CD unit works okay and doesn't need any attention? Remember that the Model 1 Sega CD uses almost  the same power supply as the Model 1 Genesis, 9 volts at 1.2 amps with the positive sheath and the negative tip.

-KKC, who should really pick up more Sega CD hardware since it fails so often.

[NES-Luke]

I'm using the Sega 9V 1.2A Power adapter for the Sega CD, and the power adapter from my SMS (9V 1A) for the Genesis, which is a model 1.

I don't have a Stereo mixing cable, nor do I even know what it is.

Sorry for the lack of details, I just got the unit last night, and information on them is pretty scarce...

[kendrick]

Without the mixing cable connecting the headphone jack of the Genesis I to the audio input on the model 1 Sega CD, the unit outputs only mono sound. I've observed one case where a short in the audio severely screwed up the video output too. But the fact that you're not using one probably rules that out.

You sure the polarity on the Sega CD power thing is correct? Not trying to be a jerk, but making sure all the obvious stuff is out of the way before Aidan gets back. :) The other thing to do at this point is to get some professional tape head cleaner (or a clean pencil eraser) and make sure the expansion slot edge connector on the Genesis is free of corrosion and debris. Rub that guy down gently, it's an extension of the motherboard and is sometimes fragile.

-KKC, who can't play Ico until he's done doing dishes.

[NES-Luke]

Both of the adapters are negative tip, positive sheath.

The one I have plugged into the Sega CD is the MK-1602 model, and the one I'm running the Genesis with is (as I said) the SMS power adapter, "Model: 3025"

Both adapters work just fine powering the Genesis, so I doubt they're the problem.

EDIT: I have cleaned the contact on the Genesis, as well as tried a few other Genesis consoles.

[Vertigo]

For reference, I neither have the mixing cable or the shielding plate and my setup works fine.

What territories are your machines? You should get a screen saying they're not compatible usually though.

Have you tried the other adaptor with your Megadrive, to check that it works ok?

When they start up for the short time, do you get any sort of video signal or an attempt at sync or anything?

Does the Megadrive function fine if you put a cartridge in, even when it's plugged into the MegaCD?

[kendrick]

After hours of exhaustive research, I have found information on the fuse that tends to blow in Sega CD 1 units. Right here on GamesX.

http://nfg.2y.net/forum/index.php?showtopic=514

Look for the thing on the upper right corner of the board labelled F01. A quick continuity test should determine whether or not it's blown, and a quick trip to Fry's should produce a suitable replacement if it is.

-KKC, reading over Lawrence's old posts and thinks that you can guess his blood pressure by counting the number of words it takes him to skewer someone for being lazy. The less words, the higher the blood pressure. :)

[NES-Luke]

For reference, I neither have the mixing cable or the shielding plate and my setup works fine.

What territories are your machines? You should get a screen saying they're not compatible usually though.

Have you tried the other adaptor with your Megadrive, to check that it works ok?

When they start up for the short time, do you get any sort of video signal or an attempt at sync or anything?

Does the Megadrive function fine if you put a cartridge in, even when it's plugged into the MegaCD?

Both are standard North American NTSC, as far as I know.

I have reversed the adapters, using the one I have connected to the Sega CD on the Genesis, and vice versa.

I get no display beyond the Genesis blacking the screen out.

Yes, the Genesis does function as normal while connected to the Sega CD.


Thanks Kendrick, I'll have a look at that.

EDIT: that guide is for the Sega CD model 2, Mine is a model 1, it could be difficult to apply that over, but the symptoms described do seem to match my problem.

I'll pull it apart again and have a closer look for blown fuses. I might have to pick up a multi-meter...

[NES-Luke]

UPDATE: I've found the only thing labeled "F1" on the board. It's near the power input, and is green, as described in the other thread.

Does anyone know what the voltage going through this fuse is? I'm lacking a multi meter, and I'm wondering if I could just use an LED or something to test continuity.

I've also heard tell of a diode that is known to go bad, the only diode I've been able to locate is directly behind the power input.

Thanks for all the help so far, and hopefully I can get this thing up and running soon

EDIT:

It was the green fuse, I bypassed it as a trial, now the unit works

I'll be going to pick up a fuse likely tomorrow.

[Paper]

Without the mixing cable connecting the headphone jack of the Genesis I to the audio input on the model 1 Sega CD, the unit outputs only mono sound.

This statement is incorrect, or atleast incomplete, and seems to go unchallenged.

1) When you connect a Mega CD (1) to a Mega Drive (1) the headphone jacket on the MD will output stereo sound of both machines. Note how the volume slider works, as always.

2) Simply inserting a jacket into the Mega CD will disable all sound from the MD through  the headphone output. There does not even have to be a wire on it as there is no actual connection between them, through these in/outputs, whatsoever. Note how when connecting the jacket in/outputs of both systems and using the L/R output of the Mega CD the volume slider on the MD does not produce any effect.

3) Using the L/R outputs of the Mega CD will give sound at any time and presumably this is in stereo (why wouldn't it, reflecting on the above?), but I can not check this at this time.

So, I do not see how it is possible to get mono sound from the Mega CD in any possible configuration.

[kendrick]

Okay, for the sake of clarification... The combined signal of the Genesis and the Sega CD is supposed to have eight channels, two produced by the Genesis and the other six produced by the Sega CD. However, the Genesis I only has a mono audio output as seen here:

http://www.gamesx.com/grafx/gen1.jpg

The only place on the Genesis I that produces stereo sound is on the headphone jack. The two pins on the expansion port connecting our two devices are separate sound channels on the Genesis II, but are not differentiated on the Genesis I. This is why the newer hardware doesn't require the mixing cable.

Therefore, if you have everything connected up without the mixing cable and rely only on the Genesis I output for sound, you will indeed only get mono sound. But you're right that using the Sega CD output ports on the back will produce a stereo signal. However, you'll be missing two channels where the majority of the sound effects are being produced. The effect is that while your Redbook music and other digitized sound will be in stereo, the majority of the game and event-driven audio will still be in mono.

One question? What do you mean by 'jacket' in the statement above? I'm not aware of any configuration that would disable headphone output on the Genesis I, unless this is referring to a specific peripheral I'm not aware of.

-KKC, late for his dentist's appointment.

[Paper]

However, the Genesis I only has a mono audio output as seen here

Sorry, I wasn't even considering that output (the mono output part of the DIN) of the MD (does anyone even use it?).

The two pins on the expansion port connecting our two devices are separate sound channels on the Genesis II, but are not differentiated on the Genesis I.

Connect a Mega CD to a Mega Drive and listen to an audio cd through the MD's headphone output for stereo sound. So the MCD -> MD connection is stereo whereas the other way around does not exist it seems. Like I said in point 3) I can not test this.

One question? What do you mean by 'jacket' in the statement above? I'm not aware of any configuration that would disable headphone output on the Genesis I, unless this is referring to a specific peripheral I'm not aware of.

You're right. It only disables the output of the Mega CD through the MD to ensure proper mixing. A misunderstanding due to me testing it while only hearing sound coming from the Mega CD. Combined with this I thought the MCD -> MD connection would guarantee it working vice versa as well. Completely neglecting the reason there is a mixing cable in the first place. /me scratches head, weird brain twist it is.

The effect is that while your Redbook music and other digitized sound will be in stereo, the majority of the game and event-driven audio will still be in mono.

Without the mixing cable and using the MD mono output and MCD L/R output this will be the case. Only using the L/R output will miss the MD output completely and using the headphone jacket on the MD as well as the L/R output of the MCD with a jacket inserted in the MCD (to cancel the MCD output through the MD) is a complete, but complex method for stereo output.

[Aidan]

The two pins on the expansion port connecting our two devices are separate sound channels on the Genesis II, but are not differentiated on the Genesis I. This is why the newer hardware doesn't require the mixing cable.

According to the schematics I have for the Megadrive I, the SL and SR connectors on the expansion bus are input only. This would allow the MCD to provide audio to the MD itself, but would not allow the MD to send audio to the MCD. Additionally, they are distinct channels when fed into the mixing opamps.

Presumably in the Megadrive II, Sega reworked the design to provide the lines as an audio bus rather than just an input. In that case, there's probably a simple resistor mixer somewhere in the MDII.

Wonder how the MCD audio bus operates? It might be possible to convert the SR and SL pins to be an audio bus rather than input only.

[kendrick]

According to the schematics I have for the Megadrive I, the SL and SR connectors on the expansion bus are input only. This would allow the MCD to provide audio to the MD itself, but would not allow the MD to send audio to the MCD.

D'oh, you're right. It makes sense in retrospect... As Paper observed, audio from the RCA jacks in the back of the Sega CD I lacks the Genesis audio channels when the mixing cable isn't present. Presumably, the output of the two jacks is the same signal generated on the SL and SR contacts.

Given that there are memory, CPU and audio inputs on the expansion slot, I have to wonder... Why wasn't the 32x connected here instead of on the cart slot? I'm inspired to check the expansion edge connector now for traces that lead to the video circuitry.

-KKC, who exercised his brain too much today. Time for some Baywatch.

[atom]

Does anyone know what the voltage going through this fuse is? I'm lacking a multi meter, and I'm wondering if I could just use an LED or something to test continuity.

Congratulations. They actually told me a reccomended fuse in that thread, but I have never put it in and have had no problems (of course i havent plugged in the wrong power supply either.)

You other guys, You guys need to seriously stop arguing about stupid techno-babble when this guy up here created his thread with a problem. You got off topic.

[Aidan]

You other guys, You guys need to seriously stop arguing about stupid techno-babble when this guy up here created his thread with a problem. You got off topic.

What's a topic for if it isn't for going off? After all, that's why forums provide a search engine.

Fortunately, NES-Luke managed to get his system working without the aid of a multimeter.  However, he never posted back to say if he managed to get a replacement fuse. Perhaps some of this stuff should be in the Wiki as well?

[NES-Luke]

I was unable to find a replacement fuse at the local Radio Shack (The Source, in Canada...) I was considering just swapping in a standard 2AMP fuse, or one somewhere in the area.

For the time being, it's still just bypassed, but I do plan to replace the fuse as soon as I can find one, because I'm loving my Sega CD

[atom]

Whatever is the smallest you can find is what I would go for, havent done any actual measurements to a SCD power usage. I just emulate now anyways.

[NES-Luke]

Whatever is the smallest you can find is what I would go for, havent done any actual measurements to a SCD power usage. I just emulate now anyways.

Well, the standard fuse was 2.5A I believe, so I was thinking 2A just for added security. I don't want to go too low and have it blow all the time.