(Topic ID: 252731)

Yet another MPU LED locked on Stern 100


By Skidave

39 days ago



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  • 14 posts
  • 6 Pinsiders participating
  • Latest reply 28 days ago by Skidave
  • Topic is favorited by 1 Pinsider

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    Stern 100 MPU (resized).jpg

    #1 39 days ago

    I just spent a few hours bringing back a Bally MPU from battery damage hell. Worked through various issues, but is booting to six flashes on the bench. The game is not quite ready for the board set yet, but soon I will finish assembling everything.

    I have a Stern 100 MPU that I have never been able to figure out, so I broke it out after my Bally repair. The LED is locked on. But, some things I do know is U9 is running (or trying to run) because I have traffic signals on my data and address lines, if I reset the U9 by grounding pin 40, the traffic signals stop. There is clocking for pins 3 & 37, but it is at a different rate than my Bally MPU.

    The LED is high from the R107 pullup resistor. It never gets a low signal from U11 and the CA2 line.

    I don't know the Stern board and if it is a 100% copy of the Bally? This board has U2 and U7. It doesn't appear that any other chips were in the U1 or U6 sockets (if you look at U10, you can see how the board color originally looked).

    I'm wondering if the MPU clocking is off. Someone did some hacky repair around U15. I have not looked at this board yet with my scope, but wanted to run this past everyone while I find more time to look at this board.

    I would just like to get this board to boot to the first or second flash. I would like to use it to test 6800s and basic tests on 6820s.

    Thanks!

    Stern 100 MPU (resized).jpg
    #2 39 days ago

    In my limited experience, this boards commonly like to shit themselves for whatever reason

    #3 39 days ago

    I paid $15 for the board at the York show last year and already used two good chips from it. I'm hoping to make it a simple test jig.

    #4 38 days ago
    Quoted from Skidave:

    I don't know the Stern board and if it is a 100% copy of the Bally?

    The Stern MPU100 is basically a clone of the Bally-17 MPU board.
    CPU clock speeds are the same - you should measure in the vicinity of 500kHz to 530kHz.

    It looks like there was an attempt to modify the board to run a single 2732 EPROM at U2. I don't see one of the mods required (maybe it was done on the back of the board).

    Carefully check that the mod was done right. Scroll down a little to "Note C, Single 2732 at U2" at this link.
    http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Bally_AS-2518-17_and_Stern_MPU-100_Jumper_Info

    The board won't boot unless it can see U2 properly.

    #5 38 days ago

    Thanks Quench.

    I was getting lost in the mods for the various EPROMs on the pinwiki page. Thanks for pointing me to 'Note C'. It looks like someone did try this modification. So far, I see E1 - E2 still jumpered (which needs to be removed) and I think they did not complete the U18 pin 5 modification. I'll put some more time into this when I get home.

    I'll report back.

    #6 38 days ago

    Ok, verified U2 is a 2732. Clock speed is 530 KHz. Modifications to the board match note 'C'. I see activity with my logic probe.

    I've come to the conclusion that U2 is bad or lost its program. I don't have a different 2732 or a burner. Nor do I have an interest in getting into burning ROMs.

    If someone wants to contribute a good 2732 ROM, please let me know.

    Thanks

    #7 38 days ago

    I'd have to double check the jumpers but I am pretty sure how you have them set the board will never boot without a U6 ROM.

    Check quench's link Note C about using a single 2732 at U2 which is for Bally -17 or Stern M100 games only. If you want to run Bally -35 software on that board see "note d"

    #8 38 days ago

    Thanks for the reply. I don't have any spare ROMs and it never looked like a U6 was installed. Again, you can see how the board changed colors and where it didn't change based on chips installed.

    I don't want to pull ROMs out of other functioning games and try to jumper this board further. I was just hoping to get it to boot and get to the first or second flash for testing 6800 chips. Plus, I like a challenge. I just don't want to go down the road of burning ROMs.

    I'll be ordering a few NVRAMs soon. Great product!

    #9 38 days ago

    The board would have left that factory with a chip in U6. It could have been baked under some HPS lights sitting on a shelf for years causing the fade.

    Compare your board to note C or D in the pinwiki link . If it is not setup shown like note c it will not boot without a U6 ROM. I am pretty sure you are going to be changing the jumpers or getting new ROMs.

    If you have no way to verify whats on that U2 chip you might be kind of stuck. I guess you could do the note C jumper and see if the MPU unlocks.

    Good to hear that you like the NVRAM modules. Thanks!

    #10 37 days ago
    Quoted from Skidave:

    So far, I see E1 - E2 still jumpered

    I just had a good look at that PinWiki mod against the schematics. Cutting E1-E2 is unnecessary. It purely relates to a signal running to the U6 ROM socket. Similar the jumper mentioned as required between E8 and E10 is actually irrelevant because it's only related to the U3 and U4 ROM sockets.

    Anyway, your problem may not necessarily be ROM related. Maybe there's a bad through hole via down the bottom of the board in the corrosion strike zone.
    Have you confirmed there's no shorts between any data and address lines?
    Are you getting activity at pin 18 of U2 (chip enable)?

    #11 37 days ago
    Quoted from Skidave:

    Plus, I like a challenge. I just don't want to go down the road of burning ROMs.

    Burning eproms is easier and cheaper than ever. Even if you don't burn any and you just have it for verification purposes.... at this point, you have no idea what's on that u2 chip. You could be changing jumpers forever and find out that someone just robbed the U6 chip out of it which is why it's not booting. No factory U2 chip from any manufacturer (well, bally/stern) will EVER boot in that situation. Visual inspection alone can't really tell if something was installed in u6.

    You could stick a logic probe on the u6 socket's chip enable signal and make sure it selects at bootup (goes low). Say it was powering up and trying to boot - without a rom in u6 I think it's going to read its bootup address as $0000 (unless the data bus is pulled high by something I'm not seeing at quick glance on a schematic). So it would blip low and then go high as it then moved to try and execute code at $0000 which will just crash the cpu. The problem is that the behavior will be unpredictable.

    #12 36 days ago
    Quoted from Quench:

    I just had a good look at that PinWiki mod against the schematics. Cutting E1-E2 is unnecessary. It purely relates to a signal running to the U6 ROM socket. Similar the jumper mentioned as required between E8 and E10 is actually irrelevant because it's only related to the U3 and U4 ROM sockets./blockquote>

    I noticed that when I sat and looked at the schematic too.

    Have you confirmed there's no shorts between any data and address lines?
    Are you getting activity at pin 18 of U2 (chip enable)?

    Did not check for shorts yet, but will.

    Yes, pin 18 of U2 has activity.

    Quoted from slochar:

    Burning eproms is easier and cheaper than ever. Even if you don't burn any and you just have it for verification purposes.... at this point, you have no idea what's on that u2 chip. You could be changing jumpers forever and find out that someone just robbed the U6 chip out of it which is why it's not booting. No factory U2 chip from any manufacturer (well, bally/stern) will EVER boot in that situation. Visual inspection alone can't really tell if something was installed in u6.
    You could stick a logic probe on the u6 socket's chip enable signal and make sure it selects at bootup (goes low). Say it was powering up and trying to boot - without a rom in u6 I think it's going to read its bootup address as $0000 (unless the data bus is pulled high by something I'm not seeing at quick glance on a schematic). So it would blip low and then go high as it then moved to try and execute code at $0000 which will just crash the cpu. The problem is that the behavior will be unpredictable.

    I agree with your logic about U6.

    I have two other working MPUs with 3 9316 ROMs and I really do not want to be using them to troubleshoot this board.

    Part of this is me wanting to 'fix' this board. I realize I am now shooting in the dark without a know good set of ROMs. At work, I have an old ROM reader / writer. It uses a DB25 connector for its serial connection. I can't remember if it is RS232 or RS422. I have 232 to 422 converters. Then I need a USB to serial converter, but ironically this is the world I live in at work.

    I saw I can buy ROMs from Action Pinball. Anywhere else to get them?

    #13 36 days ago

    hobbyroms.com

    1 week later
    #14 28 days ago

    Thanks to user slochar giving me a good 2732 ROM at the York show to solve my issue. The ROM that was in there must have been bad or never burned.

    I purchased the board for $10 and used a bunch of stuff from it. And it is now a good basic test board for me.

    For others looking to solve locked on LEDs, I usually use my oscilloscope to troubleshoot. I was really lazy with this board and just used my logic probe.

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