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Thread: Help with Mega CD II not working, please!

  1. #1
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    Default Help with Mega CD II not working, please!

    After some time looking for a Mega CD II to join with my lonely MDII, I found one unit which seemed to be perfect: not too bad on the outside and it was advertised as working with some pictures.

    I went ahead with the deal but when the unit arrived it simply did nothing.


    I'm still waiting for a reply from the seller.


    Meanwhile I took a look inside to see if I could at least grasp the nature of the fault.

    I have done some basic electronics repairs in the past but unfortunately my sight problems are giving me a headache because I have to struggle with glasses and magnifying lens (the main reason why I stopped doing this in the first place).

    Anyway, I didn't want to quit that easily so I am hoping someone could give some advice.


    It is a Sega CD2 model MK-4102 with board revision BE2200G02B02 and from what I can tell the fuse checked ok (there is continuity), but it doesn't seem to be power going to the voltage regulator NEC2405.

    What could be wrong?

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    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker
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    I'm a bit more familiar with the Model 1 CD, but I'll try to help you out the best that I can. For starters, are you using an OEM power supply or a third party power supply? The cheap third party ones can cause issues with CDs.

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    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    but it doesn't seem to be power going to the voltage regulator NEC2405.
    I would try to follow the input from the DC power jack all the way to that regulator. Try to find where the break in power is.
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    Hedgehog-in-Training Hedgehog-in-TrainingNameless One
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    Doesn't usually happen on Sega CD systems, but also make sure that the power jack doesn't need a solder reflow. They notoriously break loose on some Mega Drive/Genesis 2 systems.

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    The most common issue I've come across on the Mega CD is the Fuse blowing (similar to the SNES). This is a simple and cheap repair and easy to diagnose (check for continuity across the fuse). Essentially de-solder the blown fuse and replace with a similar one. I believe the Fuse in the Model 1 and Model 2 are different so if this is the case you'll need to find the correct one.

    I think you can use any fuse that is similarly rated - off the top of my head I think these are 1.5 or 2.5 A (or just bridge the gap - but the point of the fuse is to protect the rest of the device so if you bridge the gap and have a power surge or plug it into the incorrect supply you may fry the rest of the unit so I wouldn't recommend this )

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    Quick look found these guides that may be useful?

    Mega CD Fuse, Battery & CD Drive Refurb - https://www.youtube.com/watch?v=lzokz1qvxTw

    Fuse Replacement and Repair: Mega CD 2 - https://www.youtube.com/watch?v=dGwo-Tchehs

    Guide with pics - https://www.gamespot.com/forums/cand...pair-10017333/

    Hope that helps.

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    Quote Originally Posted by wowsux133 View Post
    I'm a bit more familiar with the Model 1 CD, but I'll try to help you out the best that I can. For starters, are you using an OEM power supply or a third party power supply? The cheap third party ones can cause issues with CDs.

    The unit came with a cheap third party power supply 9V rated at 800 mA.

    The first thing I did was to switch to a spare Sega AC adapter model 1602-05 I have.

    No, the CD drive doesn't even move.

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    Quote Originally Posted by ComradeOj View Post
    I would try to follow the input from the DC power jack all the way to that regulator. Try to find where the break in power is.
    Yes, one the of things that crossed my mind but last night I was not seeing clearly.

    I will have to look at a schematic because these components are too small and the pcb tracks seems to be covered with some coating.

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    Quote Originally Posted by Vorenge View Post
    Doesn't usually happen on Sega CD systems, but also make sure that the power jack doesn't need a solder reflow. They notoriously break loose on some Mega Drive/Genesis 2 systems.
    It's OK. I even wiggled it gently and the solders on the back are solid.

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    Quote Originally Posted by GreyFox View Post
    The most common issue I've come across on the Mega CD is the Fuse blowing (similar to the SNES). This is a simple and cheap repair and easy to diagnose (check for continuity across the fuse). Essentially de-solder the blown fuse and replace with a similar one. I believe the Fuse in the Model 1 and Model 2 are different so if this is the case you'll need to find the correct one.

    I think you can use any fuse that is similarly rated - off the top of my head I think these are 1.5 or 2.5 A (or just bridge the gap - but the point of the fuse is to protect the rest of the device so if you bridge the gap and have a power surge or plug it into the incorrect supply you may fry the rest of the unit so I wouldn't recommend this )
    Fuse is OK. I checked continuity with multimeter and there is from one leg to the other.

    I suspect there is a fault between the fuse and the voltage regulator because I'm getting no power at NEC 2405 pin 1 (nor any voltage out from pin 3).
    Last edited by MegaDriver; 07-10-2020 at 05:08 AM.

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    Doing some probing and noticed something I think it's not correct:

    -according to schematic transistor Q301 (collector?) is connected to voltage regulator pin 1 - it is.

    -again, according to schematic transistor Q301 (emitter) receives power from fuse - it does.

    But I have no voltage coming out from Q301 towards voltage regulator pin 1... Instead I have ~13V voltage coming out from base towards R303 .

    Is Q301 defective?

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    Quote Originally Posted by MegaDriver View Post
    Doing some probing and noticed something I think it's not correct:

    -according to schematic transistor Q301 (collector?) is connected to voltage regulator pin 1 - it is.

    -again, according to schematic transistor Q301 (emitter) receives power from fuse - it does.

    But I have no voltage coming out from Q301 towards voltage regulator pin 1... Instead I have ~13V voltage coming out from base towards R303 .

    Is Q301 defective?
    Console 5 sells a replacement part for Q301, maybe try replacing it? They have this as the description: "When your Sega CD 2 refuses to power on, the problem is frequently the fuse or transistor Q301. Many times you can visually spot that Q301 is bad - it will be burned, have a hole in it, or other outward sign of catastrophic failure."

    https://console5.com/store/sega-cd2-...-no-power.html

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    Quote Originally Posted by wowsux133 View Post
    Console 5 sells a replacement part for Q301, maybe try replacing it? They have this as the description: "When your Sega CD 2 refuses to power on, the problem is frequently the fuse or transistor Q301. Many times you can visually spot that Q301 is bad - it will be burned, have a hole in it, or other outward sign of catastrophic failure."

    https://console5.com/store/sega-cd2-...-no-power.html

    Thanks!

    If I can't get a proper replacement I will have to consider that one.

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    Quote Originally Posted by MegaDriver View Post
    Thanks!

    If I can't get a proper replacement I will have to consider that one.
    Oh I just realized you're in Portugal. Still though I'm sure you'd be able to find one, as long as you find the same or a compatible transistor.

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    Hedgehog-in-Training Hedgehog-in-TrainingWildside Expert majinga's Avatar
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    Check on Q301 if you have voltage from the DC jack. And check on Q302 if you have voltage from the MD when you power on the MD.

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