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Thread: Help me diagnose a Sega Genesis Model 2

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    Default Help me diagnose a Sega Genesis Model 2

    Hey all.

    I bought a Model 2 Genesis that was being sold for parts. The seller said that "sometimes it reads games and sometimes it doesn't." I took it home and opened it to check the motherboard, its a VA1.8. The motherboard itself is pristine, no sign of electrolytic leakage or abuse. The voltage regulator pumps out 5V as it should.

    I tried a few games and the results were the same: TMSS always shows and games under 16Mb always boot. When trying games that are more than 16Mb some work, some don't (Sonic3 and Street Fighter 2 work. S&K, NBA Jam TE and 6-pak don't work).

    When games do boot, sound is the next issue. It is either completely messed up (get only bass and no treble, artifacts, etc) or I get no sound at all.

    Next up, I plugged a Sega CD. It will always boot, but the sound is messed up as well.

    Does anyone have any ideas as to what might be the problem? Or maybe just something else I should check to help with the diagnosis?

    All ideas welcome!

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    Did another test: with the Sega CD connected but getting my audio from the Genesis I played a music CD. It played flawlessly so its not something simple like the capacitors dried up.

    Since I have trouble with sound from SegaCD games AND from the normal cartridge slot, the problem has to be related to one of the chips that share those communication lines. According to the schematics this includes IC1 (CPU), IC2 (ram) and IC6 (the Sega chip).

    I'd like to hear some ideas from more experienced people if you have some, please!

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    Alright, I tinkered with it for a bit again. I was after the source of the messed up sound today so I did a simple test.

    Using Sonic1, which always boots and plays with sound, I first removed the capacitors that connect the PSG (CE2 and CE5) to the amps and fired it up. I got messed up sound with heavy artifacts from the FM Synth. Reconnected the caps and removed the ones coming from the FM Synth (CE3 and CE6) into the amps. The sound coming from the PSG was perfect.

    Im thinking the Sega chip itself is damaged. If anyone has ANY ideas or can point me to a place where the sound system of the Genesis is explained itd be appreciated.

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    Nameless One Fleaman's Avatar
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    Sound like the same problem i have. Did you ever got it fixed ?

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    Electronics Engineer Road Rasher db Electronics's Avatar
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    Quote Originally Posted by slivercr View Post
    I tried a few games and the results were the same: TMSS always shows and games under 16Mb always boot. When trying games that are more than 16Mb some work, some don't (Sonic3 and Street Fighter 2 work. S&K, NBA Jam TE and 6-pak don't work).
    All these games use the nTIME signal on the cartridge connector to access save data or mapper registers. The nTIME signal is active for memory accesses in the region $A13000 -> $A130FF. Sounds like you may have a problem with that particular signal.

    Sonic3 and S&K -> the game writes to these locations to enable/disable reading/writing to the FRAM save memory.

    NBA Jam TE -> this game has a serial eeprom mapped at 0x200001 which is enabled/disabled by writing to certain registers in the $A13000 -> $A130FF region.

    Super Street Fighter 2 -> uses a mapper which is configured by writing to certain registers in the $A13000 -> $A130FF region.

    6-pak -> don't have any info on this one but surely it must use a mapper to relocate each game's code to proper 68k vector addresses.
    www.db-elec.com
    Code:
    do {
        Genesis();
    } while (Nintendont());

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    ToeJam is a wiener Hero of Algol Guntz's Avatar
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    Sounds like one or more of the upper address lines on the cartridge slot aren't working. You tried cleaning yes? If so, the only other real option you have is to get an iron and try reflowing the cartridge slot, some of the pins might have cold solder joints.

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    Ill try reflowing the cartridge slot and will post results when I am done.

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    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Hello I provide you the ultimate solutions that are discussed like 100 times already if you would try search first but here I go:

    For reading problems:

    Most likelly your problem is bad connection in cartslot. It's caused by either worn, dirty pins on slot, cold joints bottom of the mobo on the slot pins or dirty gamecart connectors. Usually that is.

    Most likelly the reason is worn, loosen slot pins that cannot make conductivity anymore. Open the case, use what you can get and try to move pins more closer to the center on cardridge slot. Also using some 2000-3000 sandpaper to sand the slot to polish the contacts a bit. It's hard the slot is tight but you can do it. You can use also alcohol/thinner to clean the slot.

    When trying games that are more than 16Mb some work, some don't (Sonic3 and Street Fighter 2 work. S&K, NBA Jam TE and 6-pak don't work).
    Sounds like what I was saying?

    For sound:

    The problem is most likelly electrolythic capacitors. These machines have a lot of elcaps on sound hardware and replacing them with new ones should fix your sound problems. Your effect sounds just like the leaked caps would behave. Nosound, carble or sometime sound. To make this matter more precise caps have what is called internal ESR which is capcitors internal series resitance. When caps ages they tend to rise their ESR and this why their resonanse shifts thus desired filter is not working anymore. When you add cap in circuit it cause usually always filter in circuit. All transitors and op-amps have their resitances which causes filter with cap. So cap degrades -> sound carbles --> nosound. And to say more, usually every cap in md audio are coupling caps and if ithey degrades --> carbling -->nosound because sound must travel trough the cap.



    That is what is called capcitor mathematic model. You will see that it is actually filter on its own. The electrolyte is the joints of the components, when it starts to dry the ESR resitance starts to have bigger in series resitanse which sifts the caps resonanse also.

    And a note:

    If you have been used the blow on your cardridges to drive your games in 90's I recommend you to use gamebit screw driver and open your games and water polish with 2000-3000 sand paper the contacts. Then the games are like new again. Remember to wait while the game mobo drys. You can make this faster with hair dryer. Components on the mobo handles 350 degrees celcius so hair dryer is not even close.

    For unbelievers: Water sanding is the best method, hands down. I get all my games working by this method right away. Alcohol/Thinner cleaning is for SEGA advertisers and beleivers how you should take care of your cart. Works many times and sometimes the contact is so worn that it has this reddish tone in the contact already. For these carts you need watersanding. Some professional repairers also use toothpaste type sanding gel and softsponge.
    Last edited by MEGADRIVE Jeroi; 03-15-2014 at 07:02 AM.
    #MEGADRIVEJeroi @ Quakenet irc server.
    Be true to yourself. GFX doesn't matter, the game does. If you are intrested to donate one NTSC Genesis for hardware testing purposes, please pm me.

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    Road Rasher Bibin's Avatar
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    Quote Originally Posted by MEGADRIVE Jeroi View Post
    Hello I provide you the ultimate solution that is discussed like 100 times already if you would try search first but here I go:

    For reading problems:

    Open the case use what you can get and try to move pins more closer to the center on cardridge slot. Also using some 2000-3000 sandpaper to sand the slot to polish the contacts a bit. It's hard the slot is tight but you can do it.



    Sounds like what I was saying?

    For sound:

    You descriped problem that exits like in 100 question already. The problem is electorlyhtic caps. These machines have a lot of elko caps in sound hardware and replacing them with new ones should fix your sound problems. Your effect sound just like leaked caps would produce. Nosound, carble or sometime sound. To correct you. If your take audio out form sega cd instead of megadrive you will get nice sound as cd don't output it's sound trough megadrive. But your megadrive game is. To make this matter more precise caps have what is called interlan esr whixh is capcitors internal series resitance. When caps ages they tend to rise their ESR and this why theyr resonanse shifts thus desired filter is not working anymore. When you add cap in circuit it cause usually always filter in circui. All transitors and op-amps have their resitances which causes filter with cap. So cap degrades -> sound carbles --> nosound. And to say more, usually every cap in md audio are coupling caps and if ithey degrades --> carbling -->nosound.

    And a note:

    If you used the blow to cardridge technology to drive your games in 90's I recommend you to use gamebit screwdrive and open your games and water sand with 2000-3000 sandpaper the contacts. Then the games are new again. Remember to wait while the game mobo drys.

    Sorry for all typos an' all, I am bit drunk atm...
    A good writeup on the principles of a cap kit, but I highly recommend against sanding anything. Any connectors that were once gold plated would lose this plating making them susceptible to oxidation very easily. I would first use a Q-tip and Isopropyl Alcohol to get grime off (once with the alcohol, once dry for better scrubbing).

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    Electronics Engineer Road Rasher db Electronics's Avatar
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    Quote Originally Posted by Bibin View Post
    A good writeup on the principles of a cap kit, but I highly recommend against sanding anything. Any connectors that were once gold plated would lose this plating making them susceptible to oxidation very easily. I would first use a Q-tip and Isopropyl Alcohol to get grime off (once with the alcohol, once dry for better scrubbing).
    Ditto, please don't sand ENIG contacts!

    Alcohol might be good to remove superficial dirt and grime, but for heavy duty contact cleaning I've never seen any solvent work as well as the "cleaning solvent" they sell at Nintendo Repair Shop. I have no idea what this solvent is, but I've been using it for years and it cleans even the worst oxydized NES games I have. Can't recommend this product enough for cleaning!
    Last edited by db Electronics; 03-15-2014 at 04:35 PM. Reason: Fixed the link
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    Code:
    do {
        Genesis();
    } while (Nintendont());

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    Quote Originally Posted by MEGADRIVE Jeroi View Post
    Hello I provide you the ultimate solution that is discussed like 100 times already if you would try search first but here I go:

    For reading problems:

    Open the case use what you can get and try to move pins more closer to the center on cardridge slot. Also using some 2000-3000 sandpaper to sand the slot to polish the contacts a bit. It's hard the slot is tight but you can do it.



    Sounds like what I was saying?

    For sound:

    You descriped problem that exits like in 100 question already. The problem is electorlyhtic caps. These machines have a lot of elko caps in sound hardware and replacing them with new ones should fix your sound problems. Your effect sound just like leaked caps would produce. Nosound, carble or sometime sound. To correct you. If your take audio out form sega cd instead of megadrive you will get nice sound as cd don't output it's sound trough megadrive. But your megadrive game is. To make this matter more precise caps have what is called interlan esr whixh is capcitors internal series resitance. When caps ages they tend to rise their ESR and this why theyr resonanse shifts thus desired filter is not working anymore. When you add cap in circuit it cause usually always filter in circui. All transitors and op-amps have their resitances which causes filter with cap. So cap degrades -> sound carbles --> nosound. And to say more, usually every cap in md audio are coupling caps and if ithey degrades --> carbling -->nosound.

    And a note:

    If you used the blow to cardridge technology to drive your games in 90's I recommend you to use gamebit screwdrive and open your games and water sand with 2000-3000 sandpaper the contacts. Then the games are new again. Remember to wait while the game mobo drys.

    Sorry for all typos an' all, I am bit drunk atm...
    Thank you. Please read all my posts again when not drunk.

  12. #12
    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Well tbh more exact 3000 sand paper is polisher not a real sand paper. And when used with water it just polishes the gold again. I usually water sand all my used games to have superior connectivity again. Shining means better inductivity and means better contact. And you are not supposed to remove the gold with any sand paper, but polish it. Ofcourse you can use cheap alchoohol tinner based methods also to clean 20 year old connector but it will not be a new again, close, but not new. Polishing means shining gold and superior connectivity.
    #MEGADRIVEJeroi @ Quakenet irc server.
    Be true to yourself. GFX doesn't matter, the game does. If you are intrested to donate one NTSC Genesis for hardware testing purposes, please pm me.

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    Master of Shinobi MaxWar's Avatar
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    I sometimes use Ultrafine steel wool for this purpose, its not very abrasive and is used to polish metals.

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    Ok.

    Just to be clear, this is not a contact problem. Contacts were cleaned before I even tried anything else. I scrubbed dry, used contact cleaner and scrubbed, waited for it to get dry, scrubbed dry again. There is no need to go beyond that.

    @Megadrive Jeroi: Thanks for your explanation on how a cap works. Perhaps it would be more useful as a single thread, it is not useful here. As I mentioned in my 2nd post capacitors are ruled out. Then in my 3rd post I pinpointed the source of the faulty audio to the FM synth. For your peace of mind though, they were changed a LONG time ago. Apart from that, I don't appreciate you coming in here drunk, shooting me down for supposedly not searching and then offering solutions that don't fit the problem because you didn't read my posts.

    @db Electronics: The nTIME signal you refer to is the one going into PIN75 of the ASIC I am guessing? Ill check for continuity and try bridging it if necessary. I doubt this is the problem though, since it doesn't explain the SegaCD's faulty sound when it boots up. Also, out of curiosity since you seem to be well versed, do you know how to probe test pins 81-84 of the ASIC (and what to expect back)? Or what pin 58 (labelled SOUND) does?

    Ill tinker with it today, post back as soon as I can.

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    Quote Originally Posted by slivercr View Post
    Just to be clear, this is not a contact problem. Contacts were cleaned before I even tried anything else. I scrubbed dry, used contact cleaner and scrubbed, waited for it to get dry, scrubbed dry again. There is no need to go beyond that.
    I beg to differ. The contacts might still be the culprit, even if they are clean. Have you made sure that none of them have been bent out of shape? After all it's a simple matter of metal touching metal. If there's just the slightest bit of air between the two, the contact fails.
    Bare Knuckle III rules! Also, the music in this game is freakin awesome.

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