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Thread: Various Hardware Problems With Mega Drive 1

  1. #1
    Wildside Expert Retropolis Zone's Avatar
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    Default Various Hardware Problems With Mega Drive 1

    I've recently picked up a VA6 Mega Drive model 1 (as is, no testing) for a few bucks that is in near flawless condition from the outside, but unfortunately half of the system doesn't work properly.

    The most peculiar and important problem it has from the moment I turned it on is that only certain games run. I've thoroughly cleaned the cartridge slot and pressed down on some of the pins on the slot to get a bit of a tighter grip on the cartridges, as well as cleaned the cartridges themselves, but none of it made a difference. Some examples of games that play are Strider, Sonic Spinball and Thunder Force IV, while others like Mickey Mania, Streets of Rage 2 and the Sonic Compilation don't play. It gets even weirder because the Mega Games 2 cartridge with Revenge of Shinobi, Streets of Rage and Golden Axe on it boots into the menu, can run RoS and SoR, but GA doesn't work for some reason. Do different games use different features of the hardware? That maybe one of the connections or a part of one of the main chips is fried?

    There are also video and audio issues. It's a unit without an RF module (the opening for it is also not in the case), but I don't get a picture with neither Composite nor RGB/C-Sync. The Framemeister doesn't receive a signal whatsoever while it does so fine on another console with the same Composite and Scart cables. Sound is how I've been able to tell whether a game boots or not, but I only get audio from the left side with a good amount of noise and the volume slider doesn't raise or lower the volume at all. My guess is that the audio problem would be resolved with some new capacitors, and maybe video as well, but it's gonna be a bit of a waste to recap most of the, if not the whole motherboard as long as the main issue of not all games playing remains.

    The screws had the typical virgin crack so the console hadn't been opened before and I couldn't notice any oddities on any of the traces or connections. Maybe one of the voltage regulators is one the fritz? Or the capacitors are to blame, after all? I don't have a multimeter so I haven't checked anything that way yet, but I'd like to hear some second opinions before I start ordering extra tools and items to see if I can fix this thing up - for all I know one of the chips is fried somehow and it's all wasted money and time.

    In any case, thanks in advance for reading this and hopefully somebody has some advice.

  2. #2
    A Light In The Building. Master of Shinobi
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    Sounds like you're trying to run PAL games on an NTSC Mega Drive. Make sure you're using a TV that accepts a 60Hz signal. Some of those games are displaying a region lockout message.

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    Wildside Expert Retropolis Zone's Avatar
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    It's probably not the region lock-out since I am testing PAL games on a PAL machine. Sonic Spinball and Thunder Force IV work fine and are games with lock-out, while Mickey Mania and Golden Axe 1 don't work and don't have lock-out at all.

    I'm thinking there must be either a bad solder joint or wire between the cart and CPU/RAM or a bad chip altogether, that causes certain games to boot while others don't.

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    since it has no RF and is a pal MD, is this an RGB Megadrive ? You can check on the label.

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    Wildside Expert Retropolis Zone's Avatar
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    So I've reflowed all the pins on the CPU and cartridge slot and got all games I throw at it to run now. However, another issue has cropped up where sometimes the audio slows down drastically, almost to the point of freezing and halting at times before it continues. I imagine this also goes for the entire game code itself, but since I get no video out of the system yet I can't determine for sure. I think the audio pitch is also lower than it should be when testing Sonic 2, for example. I know 50Hz consoles have a slightly lower pitch by default, but I can't help but feel this is off.

    Could this point to a bad chip somewhere or is this more likely an issue of power delivery? I'm a little hesitant with swapping out the capacitors and the voltage regulators, because I don't think I have quite the right tools or experience to cleanly remove through-hole components. Every time I try to do it with solder wick and a desoldering pump I can never get the holes quite emptied, making it a big hassle to get new components in and connect them properly, too. Maybe somebody here has some tips and tricks on how to get the vias completely solder-free?


    Quote Originally Posted by Ryoandr View Post
    since it has no RF and is a pal MD, is this an RGB Megadrive ? You can check on the label.
    Yeah it is actually a Mega Drive RGB.
    Last edited by Retropolis Zone; 04-29-2017 at 08:53 AM.

  6. #6
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    ok, so for the video signal, you can't get video because the composite pin is rewired directly to composite sync out of the video encoder, and also the components needed for composite are missing.
    You either need to use sega RGB adapter MK3085, or add 75 ohm resistor and 220F on the line to get a proper sync signal.

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    Wildside Expert Retropolis Zone's Avatar
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    Quote Originally Posted by Ryoandr View Post
    ok, so for the video signal, you can't get video because the composite pin is rewired directly to composite sync out of the video encoder, and also the components needed for composite are missing.
    You either need to use sega RGB adapter MK3085, or add 75 ohm resistor and 220F on the line to get a proper sync signal.
    I see, thanks for the info. Can you get C-Sync out of the Mega Drive RGB at all with the stock video encoder? I hear that Sync on Composite is noisy and I'd rather avoid it if possible, but if there's no other option then I can do that.

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    C-Sync and Composite sync are the same thing. You're thinking about Composite video as sync, which is indeed noisy.
    The RGB MD cannot do composite video anyway (unless putting back a lot of missing components). You get composite sync (or C-sync) instead on the composite video pin, comming directly from the CXA encoder, so it can't be used as-is, it need the resistor and cap.

  9. #9
    Wildside Expert Retropolis Zone's Avatar
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    Oops, my bad. The terminology is a bit confusing, haha. In any case, I would have to rewire C-Sync to the usual C-Sync pin then with the cap and resistor? Since the RGB cable I have taps into where C-Sync is located on any other console.

    20170429_142733.jpg
    So which of these pins is where Composite Video usually is and which is where Composite Sync usually is? And it's resistor > capacitor in the chain? So that I don't do them the other way around.
    Last edited by Retropolis Zone; 04-29-2017 at 09:48 AM.

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    If you're talking about sync on pin 7, on RGB Megadrive the trace just before the socket is cut (on the upper side), so you need to restore the trace.
    So with your cable that uses pin 7, you would need to restore the trace.

    Note that I've read that using this pin directly is also not recommended.
    Last edited by Ryoandr; 04-29-2017 at 10:05 AM.

  11. #11
    Wildside Expert Retropolis Zone's Avatar
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    Alright, so I got two problems out of three fixed. All games I try properly run now. Certain games not booting was fixed by re flowing all the pins on the CPU and the cartridge slot, while the freezing and halting issues seem to have been fixed by replacing the voltage regulators. I also got RGB output now by following Ryoandr's advice. Thanks man! I connected Composite Sync with the right components to the correct pin on the AV socket and that did the trick. The image is super clean too with no visible jail bars whatsoever.

    I'm trying to fix the audio issue, though. I've replaced all the caps around the amplifier circuit, but I'm still not getting proper sound from the right channel. I'm thinking it's the volume slider, since moving it up or down doesn't change the volume at all, and putting it at its lowest position gives me all kinds of weird noise on the right channel. Line-in works fine even though it's quiet, but I'd like to get the volume slider working if possible. Already tried cleaning it with rubbing alcohol and then moving the slider up and down a few times, but no luck. Is there a way to bypass the volume slider, essentially putting it at max volume by default? So that I can rule out whether the op-amp itself or the volume slider is at fault.

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    Not sure if this is possible, but since when you add external RCAs from the 1034 amp directly, the volume slider has no effect on this external audio output. So My guess is that you could just run audio straight from the 1034 amp to separate RCAs and then remove the volume slider reostat completely since, I'm not aware of an immediate replacement. If you didn't want to ruin the case of the genesis with external RCAs for audio, then I'm sure you could hook the lines from the 1034 amp directly to the left and right audio output connections at the headphone jack. That would bybass all filtering pretty much, plus the volume slider, but you would have to likely run it through an AV receiver or someway to amp the volume at that point. But for testing, I don't see why you couldn't just run the audio straight to the headphone port and disable the volume slider.

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    Wildside Expert Retropolis Zone's Avatar
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    So despite what I said earlier, I think there's a possibility of an IC somewhere being damaged. I get every game to boot now, but the system seems unstable after more testing. Some games run without any problems at all, but Monster World IV for example sometimes freezes when loading a new area. It doesn't always do this, and sometimes the music continues while the game itself hangs. It's worth noting that hitting reset does return me to the title screen proper. Alien Soldier also exhibits graphical glitches in the Weapon Select screen that come in and out seemingly randomly, with the audio getting extra crackly and noisy as the oddities come in. The main game itself runs fine. If it's actually the processor, RAM or VDP that are damaged somehow then I guess there is nothing much I can do to fix the machine.

    I would record some footage of it all, but with the perfect timing my capture card also appears to be on the fritz.

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    Did you change out the CPU at any time? Or has it been changed out? I'm asking because the symptoms you are describing sound similar to what my HDG va2 was doing. But it didn't start doing the odd graphic glitches and lockups until after I attempted a CPU replacement in the console. I added a socket to make it easier to swap out CPUs for testing. But, I still had major issues.

    Finally figured out that at least on my CPU, the socket was going to have to go. This was because solder was needed on both the bottom of the board and also on the top part of the board?! So you might try adding a bit of solder to the CPU legs again on the top component side of the board where you can just to see if it helps. In my case, doing this seemed to finally correct the graphic glitches and lockups I was getting.

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    Wildside Expert Retropolis Zone's Avatar
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    I have not swapped out the CPU and I'm fairly certain it's never been swapped out, because the solder applied looked like it came right out of the factory. In any case, I've soldered the CPU from both the top and bottom of the board and it's made no difference.

    Here's a video demonstrating some of the shenanigans going on. Alien Soldier's graphical seizure and slowdown on the weapon select screen speaks for itself, yet it runs fine when actually playing. Monster World IV footage shows that sometimes the game runs, while other times it freezes at certain intervals. These intervals are always the same ones. Sonic 3 & Knuckles title screen has garbage graphics while the in-game demo, again, plays just fine. Wonder Boy in Monster World always freezes at the title screen after pressing start. While not demonstrated here, some games like Sonic 2 and Streets of Rage 3 seem to work flawlessly.



    So I think it's a pretty good bet that either the CPU itself or the VDP is the culprit for this stuff? I've used the RAM diagnostic tool and the RAM was all fine. Cartridge slot has been extensively cleaned with rubbing alcohol and compressed air. I have not replaced any of the capacitors outside of the audio ones yet, so maybe there is a possibility there, but I don't have hopes for that. The ones in here are all Rubycon and appear fine on the outside. I've even tried a PS2 Slim adapter with its high amperage rating and it made no difference over the original power supply, so it's also not that.

    Anybody got any ideas left of what could be to blame outside of the chips or possibly capacitors?
    Last edited by Retropolis Zone; 04-30-2017 at 10:42 PM.

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