(Topic ID: 352404)

Stern Dracula Phantom Triggering Test Button

By Bservice776

4 months ago


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  • 16 posts
  • 6 Pinsiders participating
  • Latest reply 4 months ago by barakandl
  • Topic is favorited by 1 Pinsider

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#1 4 months ago

I've been trying to figure this out for a while and I can't seem to get any progress. Every now and then, my Stern 1979 Dracula will go into test mode by itself during the game. Its as if I pressed the test button once so that all the controlled lamps start blinking. The button still works as normal go advance through the rest of the tests.

It's important to note that it's very inconsistent. I can go 5 games of hitting every switch in the game and it doesn't happen and then it'll happen on 6th randomly. There never seems to be one consistent sequence or switch that will trigger it to occur. Sometimes it's right after a flip, sometimes it's in the pops, sometimes it's just rolling back down the playfield doing nothing. No consistency.

Here are the things I've tried:

- Disconnected the wires from the button itself

- Tested all the diodes on the other switches in the same column as the test button (all are okay)

- Disconnected the common wire that connects the button and all of the switches in the same column (button and all the other switches did not work obviously but the problem still occurred)

- Unplugged the coin door to eliminate anything on the coin door shorting

- Put in an Alltek MPU in place of original (back to the original board now)

- Replaced the test button with a brand new one

All of these things still had the problem occurring. The only thing that has gotten the problem to stop was disconnecting the other wire that leads to the button from the connector on the board. This wire goes directly from the button, to the connector with the rest of the coin door wires, and then directly to the MPU. No other switches share this wire.

My last idea was thinking there was a short on that wire somewhere between the coin door connector and the MPU. I ended up running a brand new wire in place of the old one to be completely sure there were no breaks or shorts in the wire. Problem is still happening.

Has anyone else experienced this issue? Any help would be appreciated, thank you.

#2 4 months ago

Replace the small capacitors on the switches in the same row and column.

#3 4 months ago
Quoted from Bservice776:

Tested all the diodes on the other switches in the same column as the test button (all are okay)

This confuses me. The test button on this era stern game just grounds the input on the mpu board it's not part of the switch matrix.

Try pulling the connector out of its housing in the head and see if it still does it. If it doesn't, there's likely a sneak short in the wire from the switch to the connector, maybe something rubbing that's grounded. If it does I'd be surprised since 2 mpu boards did it. Also hopefully there isn't something awry on your mpu board mounts where it can ground out that connector, but I'd think that's unlikely.

The capacitor you see in the schematic could be shorted, but that wouldn't affect the other board.

I'd suspect something on the coin door itself or the wire.

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#4 4 months ago
Quoted from slochar:

This confuses me. The test button on this era stern game just grounds the input on the mpu board it's not part of the switch matrix.
Try pulling the connector out of its housing in the head and see if it still does it. If it doesn't, there's likely a sneak short in the wire from the switch to the connector, maybe something rubbing that's grounded. If it does I'd be surprised since 2 mpu boards did it. Also hopefully there isn't something awry on your mpu board mounts where it can ground out that connector, but I'd think that's unlikely.
The capacitor you see in the schematic could be shorted, but that wouldn't affect the other board.
I'd suspect something on the coin door itself or the wire.[quoted image]

So if I take the wire out of the connector housing it does stop, it's the only thing that's stopped it from happening. I thought the same thing, that it was the wire sneakily shorting somewhere. I used a brand new wire and re-wired it from the button to the MPU connector to make sure it wasn't a short. Even with the new wire in and the old wire hooked up to nothing, it still happens.

It's also important to note that the MPU is missing the brackets that it normally screws into. The only thing keeping it up is a few wood screws and some spacers. It was like this since I got it and haven't found 2 brackets anywhere for sale. It sounds like I need to take another look for them.

#5 4 months ago

As long as the board isn't shorted that's fine. Maybe the button is bad.

#6 4 months ago
Quoted from slochar:

As long as the board isn't shorted that's fine. Maybe the button is bad.

I replaced the button too.

#7 4 months ago

Coin door harness???

#8 4 months ago
Quoted from slochar:

Coin door harness???

I don't think so only because I had started a game, then unplugged the coin door, and it still happened with the whole coin door disconnected.

#9 4 months ago

Maybe a whisker short on the MPU at U10?

#10 4 months ago
Quoted from Billc479:

Maybe a whisker short on the MPU at U10?

I had an Alltek MPU in it and it was still happening but I'm going to put it in again when I have the chance just to double check.

#11 4 months ago

Following this thread--i had an MPU in my Stars behaving the same way. It eventually developed other problems and finally got replaced with a Weebly MPU and the problem hasn't returned since. I tried all the same troubleshooting steps, only thing that stopped it from happening was pulling the associated female connector pin from the cabinet switch connector on the mpu (lower-right connector), disabling the test switch entirely...

#12 4 months ago
Quoted from frunch:

Following this thread--i had an MPU in my Stars behaving the same way. It eventually developed other problems and finally got replaced with a Weebly MPU and the problem hasn't returned since. I tried all the same troubleshooting steps, only thing that stopped it from happening was pulling the associated female connector pin from the cabinet switch connector on the mpu (lower-right connector), disabling the test switch entirely...

Sounds exactly the same as my situation. I'll report back once I put the Alltek MPU back in and re test it.

#13 4 months ago

The diag switch goes right to the PIA chip. So not much it can be... bad capacitor, broken pull up resistor, bad PIA socket, or bad PIA.

#14 4 months ago

So I put the Alltek board back in the game and played a bunch of games, so far the problem is not occurring again. However, a brand new problem came up. While the game was playing as it should, there was absolutely no sound at all. I ignored this for now and just continued test playing to see if test mode would come up by itself and so far it hasn't.

I turned the game off and receded the top two connectors of the MPU that lead to the sound board (two pins on the far right were unused, I believe this is normal) and turned the game back on. Now, I am greeted with an awful screeching sound as the game turns on.

Quoted from barakandl:

The diag switch goes right to the PIA chip. So not much it can be... bad capacitor, broken pull up resistor, bad PIA socket, or bad PIA.

Back on topic of the original problem, do you know which capacitor/resistor I should be looking at first? Board work isn't my strong suit so I just want to be 100% I am looking at the right things.

#15 4 months ago
Quoted from Bservice776:

I turned the game off and receded the top two connectors of the MPU that lead to the sound board (two pins on the far right were unused, I believe this is normal) and turned the game back on. Now, I am greeted with an awful screeching sound as the game turns on.

Can confirm I am stupid and mixed up the plug positions, sound is okay now, just have to confirm the MPU is the source of the originial test switch problem.

#16 4 months ago

Follow the line on the schematic. You will see it goes through a series resistor. There is a pull up resistor (between 5v and this signal) and there is a decoupling capacitor between this signal and ground.

Put your multimeter on that diag button pia pin. it should read 5v.

If it reads less than that. Power off and check that the pull up resistor is connected properly. If the pull up resistor checks good then clip one leg of the capacitor. Power on and check voltage again.

If the multimeter shows 5v on the diag button, try pushing the diag button while measuring the voltage on this pin. When the coin door diag button is pressed the voltage should come down to near zero volts.

If all that looks good then i'd throw a known good PIA in there. If it still does it then I'd suspect the IC socket is flaky. Make sure that PIA chip doesnt have a folded over leg there.

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