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.

A5.00

Tried an alternate ribbon... no change.

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.

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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

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.

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.

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!

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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.

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.

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.

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???

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.

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.

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 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.

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.

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?!?!?!

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.