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(Topic ID: 271282)

Simpsons (Stern) not booting - Color DMD Installation


By kartman_canada

4 months ago



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  • 43 posts
  • 8 Pinsiders participating
  • Latest reply 63 days ago by ChrisHibler
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#1 4 months ago

Hello all...

I installed the Color DMD kit... pretty simple to do, really. When I turn on the machine, it refuses to boot. I can press the menu button on the Color DMD board and the firmware info comes up on the new display.

After tinkering around, I found that if I disconnect the ribbon that runs from the CPU/Sound board to the Stern display board, the game boots fine. If I then CAREFULLY reconnect the ribbon, the display comes up and acts exactly as expected.

Any ideas on what to check or what might cause this behavior? I have a LOTR too so there are 'spare' boards here for me to swap and experiment with but I wanted to reach out the community first.

Any help would be appreciated. For the record, the game was running perfectly fine before I swapped the display.

EDIT: L204 on Power Driver is blinking until I disconnect the ribbon running between the CPU/Sound board and the display board. As soon as I disconnect, the L204 goes solid and the game boots. As stated before, if I then carefully reconnect the ribbon, the display starts working correctly and the game is fully playable.

#2 4 months ago

What version of the rom are you running? I believe Color dmd requires 5.0.

#3 4 months ago
Quoted from mjs2:

What version of the rom are you running? I believe Color dmd requires 5.0.

A5.00

#4 4 months ago

I’m not sure but if plugging and unplugging the ribbon cable fixes it, sounds like maybe your ribbon cable is bad and/or maybe a loose header pin.

#5 4 months ago

Either the ribbon cable or the power connection on the Whitestar display board is reversed. Red stripes on ribbon cables need to be on pin 1 - closest to the corners of the board.

Power connector should be installed with black wire closest to the corner of the board.

#6 4 months ago
Quoted from Lermods:

I’m not sure but if plugging and unplugging the ribbon cable fixes it, sounds like maybe your ribbon cable is bad and/or maybe a loose header pin.

Tried an alternate ribbon... no change.

Quoted from Dmod:

Either the ribbon cable or the power connection on the Whitestar display board is reversed. Red stripes on ribbon cables need to be on pin 1 - closest to the corners of the board.
Power connector should be installed with black wire closest to the corner of the board.

Checked and re-checked... and just checked again after reading these... Pics attached. I believe this shows all the Pin1 red stripes in the correct positions and the red led on the display board is on.

Any other suggestions would be great. Pretty disappointing. I'll try to have a closer look at the header pins.

20200619_175549 (resized).jpg20200619_175612 (resized).jpg
#7 4 months ago

I read your original post too quickly and missed the part that it was working correctly when you reconnected the ribbon cable. Try disconnecting the ribbon cable that runs to the ColorDMD to see if there's any change in the boot behavior with the wide ribbon cable.

Sounds like a communication problem between the two boards that could be due to a problem on the Stern display board board or an issue with the power connection (bad ground for example). Disconnecting the cable to the ColorDMD will eliminate a ground connection that runs back through the ColorDMD and will help to isolate the issue.

#8 4 months ago

Thanks for the quick responses!

Removed all connectors:
1) checked continuity between GND on Stern display board and chassis - Nope (expected as board is mounted on plastic standoffs)
2) connected only 5v power - continuity (i.e. GND back to chassis appears good via power connector)

Reconnected everything but the ribbon between Color DMD board and Stern display board (as requested)
--> no change to boot behavior (i.e. no boot until I disconnect the ribbon back to the CPU board)

I don't know the pinout of the ribbon but, from other reading, the blinking L204 indicates the watchdog is keeping the CPU from coming out of reset state. Something in this ribbon connection seems to be holding the CPU in reset. I did check the 5v rail by looking at the output on the lower leg of R114 and it's a solid 5.1v

#9 4 months ago

Does it work if you plug the original display back in? Is the display rom new or was it in before the display change.

#10 4 months ago
Quoted from grumppy:

Does it work if you plug the original display back in? Is the display rom new or was it in before the display change.

Just tried putting back the old display... same issue. ROM was not changed as part of this swap to Color DMD.

Anybody with L204 Blinking / Watch Dog experience? Bought a new color LED for my LOTR too. Just did the install with zero issues. I'm not blaming the display install, at this point. I'm wondering if the game was ready for an issue and it just appeared today.

#11 4 months ago

If you remove the power plug from the Stern display board will the game boot normally. If so do you still have the old cpu and display roms? maybe there is a problem with the rom on the display board causing it to lock up.

#12 4 months ago
Quoted from grumppy:

If you remove the power plug from the Stern display board will the game boot normally. If so do you still have the old cpu and display roms? maybe there is a problem with the rom on the display board causing it to lock up.

Sorry, if my previous message was unclear about the ROMs. No ROMs were changed... the chips that are in the game have been there forever (at least since I've owned it )

I've tried removing the power from the display board while booting... no impact.

One thing I noticed is that, as the L204 is blinking, the display and the TV feature on the playfield will flicker. Using my DMM, the voltage on the power connector to the display board is a constant ~5.1v. The only thing (so far) that I've found that will stop L204 from blinking and allow the game to boot is the disconnect of the 26-pin ribbon.

I tried swapping the display board out of my LOTR... exactly the same behavior.

As many will have noticed, during the startup of the display, there is a bunch of info that comes up (e.g. game name and ROM version). If I power the game, the display remains blank (flicker) as the L204 blinks. As soon as I remove the 26-pin ribbon, the game boots and the display shows the ROM version. Reconnecting the display then seems to allow the whole game to work normally.

Anyone have some knowledge of the pinout on this ribbon and the startup procedure between these boards? Something on the ribbon appears to be resetting the display board (ie. no ROM message), holding the CPU from booting, and tripping the watchdog (blinking L204). At this point, I'm pretty sure it's not the display board.

#13 4 months ago

here is the pinout for the display cable

Annotation 2020-06-20 112056 (resized).png
#14 4 months ago

grumppy Thanks very much for the pinout on the cable! Very helpful.

OK... for those following along. I inserted some discrete hookup wire between the display board and the 26-pin ribbon. This allows me to probe and such. Turning on the machine and with L204 blinking, I saw no boot as before. If I pull the RESET line (pin20), the CPU doesn't boot but the display immediately comes on with the ROM name and version. So the display board is being held in reset by the CPU and, otherwise, seems to be working correctly.

I continued to play around and found that, if I turn on the machine and pull ANY ONE of the data lines (pins 12 to 19) momentarily, it boots immediately. By reconnecting the pulled data line after I hear the 'beep', the game plays normally and the display is working as it should.

Short of trying a new set of ROM chips and/or swapping out the CPU board, I'm pretty much at the limit of my knowledge and options. Anybody have some insight into the boot process and what about the data lines might be stopping the boot from progressing?

One last thing... I don't have a scope to monitor voltages on a time scale but I did try to check the data line voltages as I powered on (no boot, L204 flashing). They seem to be toggling back and forth between 0v and 5v on a regular cadence ~1Hz.

Again, I'm hoping this triggers some ideas in someone with better insight than me.

Cheers!

20200620_152829 (resized).jpg
#15 4 months ago
Quoted from kartman_canada:

Anyone have some knowledge of the pinout on this ribbon and the startup procedure between these boards? Something on the ribbon appears to be resetting the display board (ie. no ROM message), holding the CPU from booting, and tripping the watchdog (blinking L204). At this point, I'm pretty sure it's not the display board.

The display board has it's own processor that boots independent of the CPU and displays the splash screen. After boot it waits for commands from the CPU board over the 26-pin ribbon cable.

The ribbon cable connection shouldn't really prevent the display board from booting but one of the pins is a reset from the CPU. It's possible the board is getting held in reset somehow.

#16 4 months ago
Quoted from kartman_canada: If I pull the RESET line (pin20), the CPU doesn't boot but the display immediately comes on with the ROM name and version. So the display board is being held in reset by the CPU and, otherwise, seems to be working correctly.

That makes sense. The CPU board may have a pull up that asserts the reset at power up and the CPU has to deassert it to let the display board boot.

Quoted from kartman_canada:

I continued to play around and found that, if I turn on the machine and pull ANY ONE of the data lines (pins 12 to 19) momentarily, it boots immediately. By reconnecting the pulled data line after I hear the 'beep', the game plays normally and the display is working as it should.

Sounds like the display board is loading down the bidirectional data lines with the CPU and it's interfering with something in the CPU boot procedure.

If you have another whitestar game (Stern, Sega, or Data East) you can try swapping the display boards to see if the problem follows the board.

#18 4 months ago
Quoted from Dmod:

If you have another whitestar game (Stern, Sega, or Data East) you can try swapping the display boards to see if the problem follows the board.

From post above... there are a ton of comments here from me as I weave my way through this mystery. Easy to miss.

*** I tried swapping the display board out of my LOTR... exactly the same behavior. ***

For the record: I also put the TSPP display into LOTR which booted fine --> the issue seems to stay with TSPP an not follow the display board.

#19 4 months ago

If you pull the display rom out will it boot up. I am guessing this is the only thing that stays the same when you transfer boards, cables between the machines.

#20 4 months ago

Here's the CPU board interface to the display board. You can see the pull-ups which explain why the RESET is pulled up until the CPU board boots. Additionally, the PRES (plama reset) line comes from a flip-flop that's preset high on system RESET# and remains high until it gets cleared by the CPU. The CPU isn't getting to that point in the boot procedure.

According to the manual data goes out from the display board from U201 (DATA0-7 on pins 11-18) and back through U202 (STAT0-3 and BUSY on pins 22-26). PSTB (pin 19) is the plasma strobe that latches the DATA commands into the display board.

---

When you swapped the display board, did you leave the ROMs in the boards or swap them too? Did you try swapping the 26-pin ribbon cable?

Pin 1 on the ribbon cable is a ground connection between the two boards. If that pin isn't providing a good ground connection, the two boards might have trouble communicating. The 5V power connection should also be providing a solid common ground connection through the display power supply board. You might want to check/reseat the power connectors at the display power supply board and make sure.

You may also want to try removing the cardboard RF shield from beneath the display board. It shouldn't matter as long as the foil side isn't making contact with the bottom of the display board, but you don't need it and should make sure there's nothing there contacting the board.

WhitestarDispayInterface.pdf

#21 4 months ago
Quoted from grumppy:

If you pull the display rom out will it boot up. I am guessing this is the only thing that stays the same when you transfer boards, cables between the machines.

Are you suggesting that I try to start the display board with no ROM? No, I didn't try this... But I did try putting the LOTR display board into TSPP and I started by leaving the LOTR ROM and then tried putting the Simpsons ROM into the LOTR board. None of these experiments produced any change... no boot until the 26-pin ribbon is disconnected.

#22 4 months ago

That is what I was thinking. now after reading this I started by leaving the LOTR ROM and then tried putting the Simpsons ROM into the LOTR board. I don't think it will do anything helpful. My thought was that the Simpsons rom may have been holding it up.

I am starting to think that the problem is on the cpu/sound board.

#23 4 months ago

dmod thanks again for the details - the schematic is super helpful. I'm an engineer but not an EE though. As a Mech, I have some digital circuit training. This would be fun and educational if it wasn't driving me crazy!

1. I've tried swapping the ribbons - no change
2. I've tried removing the RF shield - no change (for the record, the foil side was down already)
3. I tried swapping the display ROM - no change

So the CPU boots when the ribbon is disconnected... specifically when one of the data lines. From all the swapping (including the original DMD back in), I'm feeling like the display board is not the issue. This means CPU board or the Driver board...

Assuming the display board is not the cause, what on the CPU board could be 'wrong' that would prevent boot? Same question but on the Driver board: what are the potential issues on the driver board that would leave L204 blinking? I'm trying to wrap my head around the whole boot process and which board is the cause of the hold up.

#24 4 months ago
Quoted from grumppy:

That is what I was thinking. now after reading this I started by leaving the LOTR ROM and then tried putting the Simpsons ROM into the LOTR board. I don't think it will do anything helpful. My thought was that the Simpsons rom may have been holding it up.
I am starting to think that the problem is on the cpu/sound board.

I'm in agreement but this is only based on experimentation and not based on specific circuit knowledge. I don't feel like the cause has been identified yet.

what are the chances that the main ROM is the culprit? I don't have a spare one of those... I'm a bit reluctant to swap the CPU or Driver out of my LOTR because it's working. I don't have a spare of either of these in a box and have already been looking for a source of replacements. Having spares around has long been a plan.

Should I be looking for Stern boards or a drop in replacement option with a modernized design???

#25 4 months ago

This may help some from the manual.

Annotation 2020-06-21 104112 (resized).png
#26 4 months ago

It does say the plasma reset is software controllable.

#27 4 months ago
Quoted from grumppy:

It does say the plasma reset is software controllable.

Are you suggesting that the main TSSP ROM is a potential cause because the 'software controllable' Plasma Controller line is not doing it's job? The 'splash screen' on the display comes up if I pull the reset pin. So, I'd say it's correct that the CPU board is holding the Plasma Controller in limbo.

I found and probed the Plasma Reset TP. When the machine is on but not booting (L204 blinking on Driver), the TP is bouncing between +5v and 0v. I can't be more precise because I'm using a DMM and not a scope. I pulled a data line to get the machine to continue to boot and, as expected, the TP is then held low. (i.e. the display is up)

The question I'm looking to answer is what specifically is the CPU waiting for...

Is some cue missing from the Plasma Controller? My guess is the issue is not on the Plasma Controller.
Is the Power Driver board blinking L204 because of the CPU or or is the CPU not booting because of the Power Driver?

Frustratingly, I'd really like to understand why pulling any one of the data pins triggers the CPU to continue booting.

#28 4 months ago

Is there any harm in putting the LOTR main ROM into the TSPP? I'm sure the game will be a mess but I'm curious to see if it boots.

#29 4 months ago
Quoted from kartman_canada:

Is there any harm in putting the LOTR main ROM into the TSPP?

Display or game ROM?
Display ROM will not cause any issues other than wrong animations.

Game ROM can cause some issues with coils. So you would need to disconnect the connectors that go to the coils.

#30 4 months ago
Quoted from PinballManiac40:

Display or game ROM?
Display ROM will not cause any issues other than wrong animations.
Game ROM can cause some issues with coils. So you would need to disconnect the connectors that go to the coils.

Makes sense... I was specifically referring to the game ROM... How about I leave everything connected but open the coin door to disable the high voltage stuff? I really just want to see if the TSPP board boots with an alternative ROM chip installed.

#31 4 months ago

It looks like A0 from the game rom (u210) is the address that is the software control for the plasma reset on u216.

pr (resized).pngrom (resized).png
#32 4 months ago

From everything that's been described, the most puzzling thing to me is why disconnecting one of the DATA output signals from the the CPU to the display board has any effect on the boot procedure. It would be less surprising if the behavior changed based on pulling the BUSY or STAT input signals to the CPU.

The DATA line connections on the display board are shown below. They go to a bus transceiver that only lets the data through to the MC6809 (display controller) when it's trying to read data from the CPU board. The BD lines at the output of the bus transceiver are the MC6809 data bus. That bus is used to read the display ROMs, read CPU data through U2, and write STAT output data to U7.

The BUSY line is the IRQ that goes to the MC6809. I think the Xilinx chip on the board raises the IRQ/BUSY in response to a plasma strobe (PSTB). This tells the MC6809 to go read the data that the CPU is sending and lets the CPU know that data is being read. It's possible that BUSY (or STAT) isn't behaving properly on the CPU board (problem at U202 or the input resistors/capacitors) and the software is getting hung.

DisplayBoard (resized).PNG

EDIT: I just looked at the Data East display board which is an earlier version of the Stern board with more discrete logic that makes it easier to see how the display board works. I can confirm that BUSY is set high by the plasma strobe and cleared when the MC6809 sets PORTIN low to read the data from the CPU.

DEDisplayBoard (resized).PNG

#33 4 months ago
Quoted from kartman_canada:

Makes sense... I was specifically referring to the game ROM... How about I leave everything connected but open the coin door to disable the high voltage stuff? I really just want to see if the TSPP board boots with an alternative ROM chip installed.

I don't think that will work that easily. I understand that most of these Whitestar games have a PAL chip on the CPU board that is game specific. If you swap it with the game ROM, then it should boot if the CPU board does not have another issue.

I imagine leaving the coin door open may work, but I'm always on side of caution.

#34 4 months ago
Quoted from PinballManiac40:

I understand that most of these Whitestar games have a PAL chip on the CPU board that is game specific.

The PAL on Whitestar is not game specific. It's for address decoding.

#35 4 months ago
Quoted from CoreyStup:

The PAL on Whitestar is not game specific. It's for address decoding.

I tried swapping the PAL between Harley Davidson and Sharkey's Shootout and found that will not work.

#36 4 months ago
Quoted from PinballManiac40:

I tried swapping the PAL between Harley Davidson and Sharkey's Shootout and found that will not work.

Sharkey's is an anomaly with its PAL at U213. It had 32K of RAM installed (and used it), where most have 8K.

The PAL to decode 32K of RAM was marked with a "GOLD DOT". Most are 8K games, marked "BLUE DOT". TSPP and LOTR are both blue dot games.

#37 4 months ago

Just some additional information regarding L204:

According to page 135 of the Simpsons Manual (https://sternpinball.com/wp-content/uploads/2018/11/The_Simpsons_Manual.pdf)

L204 shows the reset state of the I/O Board. If the LED is flashing this means that the watchdog is not being fed by the CPU/Sound Board and the I/O is oscillating into and out of reset.

The watchdog is fed by the scanning of the light matrix. More specifically Pin-19 of U6 must be toggling once every 50ms to prevent the watchdog from resetting. The scanning of the light matrix is controlled by the CPU through J1.

---

It's possible the CPU is booting, but something is preventing it from sending the watchdog signal to the I/O board and the I/O board keeps resetting.

#38 4 months ago
Quoted from Dmod:

The watchdog is fed by the scanning of the light matrix. More specifically Pin-19 of U6 must be toggling once every 50ms to prevent the watchdog from resetting. The scanning of the light matrix is controlled by the CPU through J1.

I can try to borrow a scope from work but, before I go there, I assume this scanning you detailed is happening after I pull a data line on the Plasma Controller. Once the game boots (I'm saying 'BOOT' = L204 going solid and the machine going BEEP), the game is fully playable.

Quoted from Dmod:

It's possible the CPU is booting, but something is preventing it from sending the watchdog signal to the I/O board and the I/O board keeps resetting.

How can I test the state of the CPU? Once out of reset and game is booted... if at any time Pin19 of U6 stops getting it's 50ms toggle, does the board drop back to reset and L204 blink again? I'm asking because, as already pointed out, the game is fully functional once booted. This seems to indicate that all the mechanisms/paths/signals are working but, at power up, some condition is not being met and the boot process is stalling.

I've ordered a CPU board. Even if that doesn't fix the problem, I have 2x games that use this board and always wanted to have one in backup. Of course, if it fixes the issue, I want to get this board repaired so I have a functional backup. This means understanding what to repair.

dmod
Once again... the interest in this issue and insight has been invaluable. Thank you.

#39 4 months ago

I don't have any knowledge of how the CPU code operates. CoreyStup, who's already on this thread, or OrinDay who is also on Pinside may be able to provide some direct insight.

I suspect the scanning must be tied to a periodic interrupt which is masked off during bootup and the boot procedure just isn't completing. I haven't found anything that would indicate why a removing a DATA line would have any impact on the boot procedure.

You might want to experiment with the FAST BOOT setting under the Standard Adjustments menu. Changing that to YES seems to skip some checks at power-up and might bypass a check that is hanging the CPU.

#40 4 months ago
Quoted from Dmod:

You might want to experiment with the FAST BOOT setting under the Standard Adjustments menu. Changing that to YES seems to skip some checks at power-up and might bypass a check that is hanging the CPU.

Well... The FASTBOOT seemed to have been the default (i.e. it was already on YES). I set it to NO and the game did a reset automatically. This resulted in the stall as before. Bummer! I then went back into the service menu and set FASTBOOT back to YES. Interestingly, this time the auto reset happened, I saw L204 shut off briefly and then it came back on solid and the game booted without any interference from me (i.e. pulling the Plasma Controller ribbon.

Not ground breaking but it seems that whatever is stalling the boot on cold power up is happening on a warm non-fastboot but bypassed on a warm fastboot.

Maybe this will prompt some new neurons to fire?!?!?!

2 months later
#41 63 days ago

OK... took a long time but I bought a new CPU/Sound board (wanted a spare anyway). Swapped ROMs, installed, and powered on...

Game now boots correctly. Clearly there is something up with my CPU board that was not reading the display ribbon correctly and the CPU board was holding the Power Driver in reset.

Now I'm looking for a knowledgeable person that can read/digest this thread and repair my original board... recommendations welcome.

Great community. THanks sooooo much.

#42 63 days ago
Quoted from kartman_canada:

Now I'm looking for a knowledgeable person that can read/digest this thread and repair my original board... recommendations welcome.

Try borygard (Rob Anthony) or ChrisHibler

Both are very skilled at board troubleshooting and repair.

#43 63 days ago

Happy to help.
Drop me a PM.

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

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