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Thread: Sega CD systems repair thread

  1. #721
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    Ok i'm confused.

    So i bought a jap mega cd 1 a while back, broken, wont power up etc.

    Now in my earlier posts , i have opened it up and i saw that the ribbon cable was damaged. So i ordered a new one (see above) and a poster here told me that was the correcct one.

    Now i have investigated the main and sub board with a multimeter, testing all the fuses and capacitators and all soms working.

    From what i see on the boards, no leaking capacitators either so , i reassembled , hoping that fixing that ribbon cable would do the trick but still nothing at all

    No power up, nothing.


    I also used a PAL asian MD and a EUR pal MD on top , it seems that might not be a problem in booting up and playing.

    As for the ac adaptors, i used original MD adapter (220) and a original jap mega cd 1 adapter (110 - with transformer to 220)

    Any idea guys??

    Thanks

    Or do you need to have a jap MD instead so the jap Mega cd 1 boots? I thought not?

    Edit: could it be TR4 that might be broken? See foto:

    megacd_TR4.jpg
    Last edited by SPiET; 01-09-2020 at 06:09 AM.

  2. #722
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    Tr4 don't look good. Better to check It.

    You can use any MD with any MCD. At worst It will show a message like "this system Is not made to work with ..."

  3. #723
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    Hi there,

    Yes it doesnt but i checked it with a multimeter and it still works.

    However f1 isnt so need to replace that.

    And i was thinking to replace the voltage regulator too (on IC6) however i can still measure some voltage , same for TR4. Should they got to the maximum voltage when measuring or not?

    And for the capacitators on the sub board, some has activity while others not (is that normal? however sometimes difficult to test since some of them are pretty close to the board attached)

  4. #724
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    How do you get some voltage if the fuse is open?


    Tr4 is a darlington transistor. It act as a power switch for the MCD. You must find voltage only on one side when is off, and on both when is on. And about 5V on the base when the MD Is on and nothing when is off.

    About the caps only the smd ones are recommended to change. But, if you wanna go for a full recap Is ok.

  5. #725
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    majinga: its resistance, i think not voltage;. setting on my multimeter RX 1K.

    If you look at the picture of the mainboard TR4 looks like brown residu next to it.

    And if i measure resistance on F1, nothing at all. Or am i doing something wrong? If i put my multimeter , one on the left leg of F1 and the other on the right, i should see something on my multimeter no? (when the mega cd is off)

  6. #726
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    Quote Originally Posted by SPiET View Post
    ... i should see something on my multimeter no? (when the mega cd is off)
    Correct. The fuse is gone.

    TR4 doesn't look good to me. I will replace it.

  7. #727
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    Yep doing an order now for those things.

    Btw TR4, is it just desolder on top? the left and right pins since it isnt attached through the pcb? (sorry pretty new in soldering )

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    Quote Originally Posted by SPiET View Post
    Btw TR4, is it just desolder on top? the left and right pins since it isnt attached through the pcb? (sorry pretty new in soldering )
    Sorry, it's not clear to me. What do you mean?
    TR4 is an SMT component. Probably a to-252 or 263. Do you need some advice on how desolder it?

  9. #729
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    Yes please since i dont see any pins going through the pcb to desolder it.

  10. #730
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    That's because it is a surface mount component.
    I would remove it with hot air. Probably is possible to use something like the chip quick to desolder it, but i would not use this method. Or just two Irons.
    Or you can cut the two little legs, and desolder one piece at time.
    Whterver you choose to do, be careful. The pad under the component can be damaged. You risk to tear it away, and end with more work to do. If you are not confident with this kind of work, i suggest you to do some pratique on some other board first.

  11. #731
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    I have an update on my broken mega cd! So, I've been able to get a spare Sega CD main board off a buy and sell group. The issue I currently have is faulty ram/ic chips leading to pcm audio glitches with my current main board. This new main board is the same model no. as the old one ignoring the NTSC bios & timing crystal but has the ram chips needed. While I could just swap the ram out and call it there I've got another idea. The new board is in much better condition so it makes sense to use it instead. Swapping out the bios chip seems easy enough but the real question is what will happen when I slot a pal bios in a board with a 60hz timing crystal? What would happen if I ran a pal game and switched to 60hz on a modded megadrive during gameplay? Are there any advantages to leaving the 60hz crystal in, or will I just get timing issues in pal games? Any insight welcome!

  12. #732
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    Quote Originally Posted by Kamon View Post
    I have an update on my broken mega cd! So, I've been able to get a spare Sega CD main board off a buy and sell group. The issue I currently have is faulty ram/ic chips leading to pcm audio glitches with my current main board. This new main board is the same model no. as the old one ignoring the NTSC bios & timing crystal but has the ram chips needed. While I could just swap the ram out and call it there I've got another idea. The new board is in much better condition so it makes sense to use it instead. Swapping out the bios chip seems easy enough but the real question is what will happen when I slot a pal bios in a board with a 60hz timing crystal? What would happen if I ran a pal game and switched to 60hz on a modded megadrive during gameplay? Are there any advantages to leaving the 60hz crystal in, or will I just get timing issues in pal games? Any insight welcome!
    I don't think the crystals are different between NTSC and PAL territories for the Mega CD. The Genesis M68K runs at different clock speeds 7.67 MHz for NTSC and 7.61 MHz for PAL and has different crystals. The Mega CD M68K runs at 12.5 MHz for both NTSC and PAL. The only differences between regions are BIOS and the logos and stickers on the units themselves from what I'm aware of.

  13. #733
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    ok thanks for the info.

    Well i would try to desolder it from the top. Starting with leg 1 and 2 and then around it (since there is solder there too).
    Attachment 15254

  14. #734
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    Again, no attachment.
    You must melt the solder on each PIN together. Try to bend the single PIN is risky, you can apply too much force on the central pad.

  15. #735
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