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Mega Drive Model 1 troubles

Discussion in 'Technical Discussion' started by Xanvier, Jun 21, 2016.

  1. I have this poor guy just sitting here in my room and I'm trying to get it working, but nothing really looks off other than the CPU itself (as well as the board being greasy as all hell, need suggestions on that as well).

    Board image

    The CPU appears to be fried unfortunately, it looks brown right in the middle of the package (around the die).

    CPU image

    Upon turning on the console, all I get is a black screen, no TMSS (if it has it, I'm inexperienced with Sega hardware) nor does the game start. As for sound, I get the usual noisy output and pops whenever you turn on/off the console.

    I am a trial member still so if anybody can help me to point in the right direction on what to do or which CPU to get (if it is the CPU), please contact me over PM.
    (waiting for exams to finish so I can continue working on that mod from like 2013 :V)

    If you do need better quality images, I can provide, it's just that I have taken these at night a few days ago without much thought put into it. Also, I did try Sega-16 but my account never got approved.
  2. Aesculapius Piranha

    Aesculapius Piranha

    つづく Oldbie
    The Genesis had the Motorola 68000 as its primary CPU, though I'm not quite savvy enough with the tech stuff to tell you if replacing your CPU is the way to go or not.
  3. Before you replace the 68k and waste another CPU, you might want to desolder it, check for shorts, measure in and output voltages of both 7805 regulators to verify the rest is working okay. Chances are that whatever fried that 68k fried something else too.
  4. So it is the CPU that's dead? I don't wanna go onto a desoldering foray without being sure that it is. (due to lack of proper tools, I only have a pump but I think I can manage it out at my school, they probably have proper tools)
    If it is I'll order a socket for it so I don't screw anything up. Thanks for suggestions though! I'll check voltages of 7805s, IIRC they were 4.95V or so with a multimeter but I'll check again, this is just coming off of my memory. I'll edit this post accordingly to save some posts. :v:
    By the way, are there any traces on the board that are supposed to short any legs of the ICs?

    EDIT: Both 7805s are Motorola ones, first one (closer to the back of the console) shows 4.98V, second one shows 5.01V, so it is pretty good there on the outputs. Inputs show 8.33V on both of them. Only suspects I've noticed as far as shorts go (without desoldering the CPU yet) is that Vcc is going to pin 22 and 25 of the CPU and I haven't seen any traces on the board to suggest that so I think that's shorted inside the CPU itself.
    BTW I'm powering it off of a 9V 1A adapter, I don't have the original one, that's also what I should've mentioned. The CPU was DOA anyway, I've opened the console up before powering it.
  5. GerbilSoft


    RickRotate'd. Administrator
    Pin 22 = /BERR
    Pin 25 = /IPL0

    Both of those are unused on MD and should be pulled up to +5V, though I'm not sure if that's normally done using a pull-up resistor or a direct connection to Vcc.