(Topic ID: 326411)

Zero Crossing not detected on Stern Dracula

By micronut

1 year ago

Topic Stats

  • 9 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by Quench
  • No one calls this topic a favorite


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#1 1 year ago

I just acquired a Stern Dracula and this is my first restoration. I had the MPU flashing 7 times then I noticed the solenoids misfiring so I took both the MPU (which is a Bally MPU) and the Solenoid board out to check and resolder the pins for the 4 lines going to the decoder on the solenoid board. When I reconnected everything the MPU only does 6 flashes.
I checked U11 test points and all voltages are correct.
TP3 is correct 21.5V.
Put an oscilloscope to TP3 got 120 Hz signal.
Tested pin 18 of U10 got 0.25 V on meter with a short positive 5V pulse at 120 Hz on the oscilloscope.
Swapped U10 and U11
Disconnected Sound board
F4 fuse is good
Still only 6 flashes but it does look like it goes into attract mode and some of the self diagnostics give odd displays. Also I have heard a loud buzz from speaker at random times when the sound board is connected. I also hear the relay for the flippers activate.
I did notice the plug for J1 of the MPU is 2 plugs (one keyed and one not). I'm assuming that the non keyed plug may have been misaligned damaging the 6800. Is this a safe assumption or am I overlooking something.

#2 1 year ago
Quoted from micronut:

Still only 6 flashes

Does the MPU LED go completely off after the last flash or is it on dimly?

If you're able, post a video starting just before powerup that then shows the LED flicker/flash sequence as you power up.

#3 1 year ago

The Led does not look as if it is on after the flashes. Here is a video of the flashes.

The flash at the very end was due to turning off the pinball machine.

#4 1 year ago

I can see the LED glowing at the end of the flash sequence.

#5 1 year ago

the mpu is booting up all the way. i'm honestly surprised it is with those orange sockets, they are pretty unreliable.

Wrong counting of every display is probably a missing display BCD data which comes out the MPU at J1. Look for cracked solder joints or broken crimps. The PIA chip socket is potentially a problem. If the ports are open circuit, the power on test won't catch that.

#6 1 year ago

Thanks for all the replies. I appreciate the help. I was getting a little discouraged but now I feel I'm back on track.

Yes the sockets are questionable. When I first got the pinball machine the LED was solid at boot up. I made sure the ICs were reseated and then it booted. I'll add getting machined sockets to my todo list and replace them. It's good to know the MPU is working. The solenoids aren't firing anymore but that probably is a bad connection on the 43V line on the solenoid board. I'll look into that next. Thanks again!!

#7 1 year ago
Quoted from micronut:

The Led does not look as if it is on after the flashes. Here is a video of the flashes.

As others have said, your board is booting normally showing the following LED sequence:
flicker (at power-on)
flash (ROM test passed)
pause (takes time to do the 6810 RAM test)
flash (RAM 6810 passed)
flash (RAM 5101 passed)
flash (PIA U10 passed)
flash (PIA U11 passed)
flash (Display generator interrupt received passed)
flash (Zero crossing interrupt received passed)
on very dimly (game reached attract mode and the display refresh service is running as expected)

The nicad battery on the MPU board needs to be retired before it starts leaking and corroding the MPU board.

Your solenoid, display and sound problems sound like connector issues. Have you done any work in this respect?

#8 1 year ago

@Quench, I have done a little resoldering of the connectors but not all of them. I'll do them all and if needed recrimp the plugs as well. The person I got it from had it serviced once and it was working for him then stopped (I feel that was the unreliable brown sockets caused it) then sat unused for 10 years. I am planning on getting a NVRam replacement and removing the Nicads too. Thanks.

#9 1 year ago

How about reterminating (i.e recrimping) the connectors?

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