(Topic ID: 242642)

Centaur Help

By spocek

7 months ago

Topic Stats

  • 27 posts
  • 10 Pinsiders participating
  • Latest reply 5 months ago by spocek
  • Topic is favorited by 4 Pinsiders


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There have been 6 images uploaded to this topic. (View topic image gallery).

sounds (resized).jpg
Alltek Centaur  Game Settings DIP (resized).jpg
Alltek Centaur DIP (resized).jpg
Alltek solenoid board (resized).jpg
new Alltek boards (resized).jpg
Centaur (resized).jpg

#1 7 months ago

I bought the machine about 3 months ago and it worked fine. I turned it on yesterday and it does not work. The lights are on behind the back glass and only 3 lights are illuminated on the playfield. The first light on the left blinks and the other two are solid red.

I am new to owning pinball machines and am still learning the ropes so any help would be greatly appreciated.

My Centaur has the old fashioned power cord (no ground prong) but I would disconnect it from the power outlet when not in use. I hope to either replace the cord with a standard grounded 3 prong type or plug the existing cord into a powerstrip.

Should I look at the MPU and see if it blinks? Could it be a blown fuse?

Thank you.

Centaur (resized).jpg
#2 7 months ago

Yes, see if the cpu blinks 7 times. Pull fuses and check them with a multi meter. Burnt connectors, battery corrosion etc.

#3 7 months ago

Lift playfield and check the fuses 1st. If all are good, remove the backglass, open the head and look at the top left circuit board. Turn the game one and count the number of times the LED flashes.

#5 7 months ago

Replace that power cord first then go through the logical troubleshooting sequence referenced above.

There's lots of information on this site explaining how to replace a power cord. Good luck and let us know how everything is going.

#6 7 months ago

Thanks. I will try out your suggestions next week and see if any of it fixes the problem.

#8 7 months ago
Quoted from Billc479:

Replace that power cord first then go through the logical troubleshooting sequence referenced above.
There's lots of information on this site explaining how to replace a power cord. Good luck and let us know how everything is going.

While replacing a worn power cord or one missing the ground post is a great idea, I doubt that why this previously working game doesn't start now. It's lighting up indicating it's getting power. Not every game needs a new power cord.

Check fuses 1st, count MPU flashes 2nd.

1 week later
#9 6 months ago

I just checked the MPU. I get a solid green light on the MPU LED. There are five fuses next to the transformer. None of them look black (not sure if the fuse glass turns black when the fuse burns out) - I guess the only way to check if they need to be replaced is to use a voltmeter.

I have noticed that when I open the headboard door the lights from the top of the playfield (see the previously posted photo) turn off and the lights inside the queen's chamber light up. I guess at this point checking the fuses is probably the best route.

#10 6 months ago

You'll need to use a DMM to test the fuses. Also, changing the power cord is a good idea. Was there anything done to the game before it stopped working? Though some machines may break just by looking at them, it seems odd that "out-of-nowhere" it just stopped booting, but things do happen without us knowing.

#11 6 months ago

From the pinwiki link listed above. Start here:

5.5.4 Bally / Stern MPU Board LED Flash Sequence
Upon start up, Bally and Stern boards have an LED that flashes. The LED is used to convey the results of specific tests conducted on various parts of the system. This section explains what is being tested and how, according to information from the Bally "FO-561-2 Theory of Operation rev. 5-1982" manual, and the Stern manual "Theory of Operation, Stern's Microprocessor Controlled Solid-State Games".

When power is first applied to the MPU board, the LED by default is ON. The very first set of valid instructions in every Bally / Stern game is to turn the LED off. This is more of a flicker than a flash, so is not counted as a flash in the 7 flash sequence. Quick summary
Flicker: MPU reset good, program booted.
1st Flash: ROM Checksums OK
2nd Flash: U7 6810 ram OK
3rd Flash: U8 5101 ram OK (U8 & U13 on mpu-200)
4th Flash: U10 PIA OK (see details for caveats)
5th Flash: U11 PIA OK (see details for caveats)
6th Flash: U12 555 Display interrupt timer OK
7th Flash: Zero crossing interrupt detector OK (solenoid voltage present)

The LED isn't flashing based on what you're telling us. It just stays lit when you turn the game on correct?

#12 6 months ago

I have two LEDs. The upper right board (MPU) LED is solid green when I turn on the machine while the bottom right board (lamp driver) LED displays 5 flashes.

#13 6 months ago

The bottom right board is the sound board. It is supposed to flash 5 times.

#14 6 months ago

Is the battery still attached to your MPU? Is there corrosion? Have you looked at the MPU closely to see if there are cracked solder joints, broken/burnt traces etc?

#15 6 months ago

I decided to post a short video about my Centaur problem. My understanding is that during the boot up the MPU board is supposed to flash 7 times while the sound board is supposed to flash 5 times. I incorrectly refer to the two in the video.

#16 6 months ago

I may need to go shopping again at Marco Specialties:


#17 6 months ago

You don’t need a new mpu. Get out your meter and check the dc voltage on the mpu at the test points. Go to pinwiki online for the appropriate test points and values. Also make sure to check the connectors on the mpu. Might just have a loose connector. Bottom left connector on the mpu is labeled J4 on the board. Unplug it and plug it back in fully. Without 5v and 12v the mpu will not boot. Your led is stuck on instead of flashing 7 times. Check the 5 volt test point first.

2 weeks later
#18 6 months ago

I unplugged all 4 cables on the MPU and plugged them back in. I got the same result - I have not tested the voltages on the MPU but chances are that if there are problems on the MPU I might as well replace the whole board as I would not know how to fix it. The MPU light continues to be solid green.

#19 6 months ago

I ended up ordering a new MPU, Solenoid, and Test board from here: https://allteksystems.com/products-mpu-replacements.html

I gave up after reading the following and decided to just replace the boards:

No Flashes: the LED is Permanently On:

If you turn your Bally game on, and the LED stays on continually, this is one of the hardest problems to fix on these boards. A stuck on LED can be caused by any (or all!) of the following:

The reset circuit is damaged (after all, it's in the battery corrosion area!). This includes transistors Q1 and Q2 (both 2N3904), Q5 (2N4403), and diodes CR5 (1N4148 or 1N914) and VR1 (1N959B or 1N4738A).
The program ROM (read only memory) at U6 is bad.
The ROM jumpers are incorrectly set for the U6/U2 ROMs installed.
The U9 CPU microprocessor is bad.
The U11 PIA (peripheral interface adapter) is bad.
ANY of the sockets for chips U6, U9, U11 are bad.

The first and last points are probably the most common problems.

Copied from: http://techniek.flipperwinkel.nl/ballyss/rep/index2.htm#fixture

#20 6 months ago

I would say that you have connector plug problems.

Even if you change the MPU out if you do not replace the female connectors that plug into the board you may still have the same problem.

I would try, while the game is on, wiggling the connectors that plug into the MPU and see if anything lights up or changes. Easy to do and costs nothing to try.

#21 6 months ago

After watching your video your green light on thr MPU is not flashing. That's the board in the upper left corner. It looks to be stuck on. It needs to flash 7 times and then stay solid green. So something is wrong with the board.

#22 6 months ago

I will try reconnecting all 4 MPU connectors while powered on and see what it does. I also came across another great resource on fixing Bally pinballs (1977 to 1985):


#23 6 months ago

Reconnecting the MPU female connectors had no effect other than showing a new playfield light pattern (around dozen of the playfield lights were illuminated) when the bottom left female connector was not plugged in and the other 3 female connectors where plugged in. My next step is to replace the MPU board.

1 week later
#24 5 months ago

as someone who has worked on games like Centaur for 30 years I can tell you that replacing the electronics with Alltek boards solves a lot of inherent problems with that era of machine. This will make the game much more bulletproof down the road.......

#25 5 months ago

The MPU is the board in upper left. Your video is incorrectly focused on the S&T board which has it's own series of flashes and not your problem right now.
The LED on the MPU, when your camera is on it, appears not to flash at all. Something on the MPU might be at fault, but before you start throwing boards at the problem I advice checking voltages. Try unplugging all the connectors from the mpu except j4 and see what that does. Hold the cammera steady please and give us viewers a close look.

#26 5 months ago


You are right -I did make a mistake in the early part of my video confusing the MPU and S&T boards but I did correct myself later on in the video. Like I said, I am new to repairing pinball machines. Thanks for your feedback.

#27 5 months ago

I am happy to report that I have repaired my Centaur pinball machine. As Startek2 mentioned the key to repairing it was replacing the MPU board. I also went ahead and replaced the solenoid board. I chose Alltek boards as they are fantastic in both design, quality, ease of use and price. Alltek's MPU board covers any solid state pinball machine. Also, they enable free games.


I have attached the newly installed board images.

Once you replace the MPU board make sure to set the DIP switches as indicated on my photos. The last step is configuring the audio settings:

1. Turn the game on.
2. Open the coin door.
3. Push the small button inside (Self-Test button).
4. This will start testing and setup. Look at the backglass and push the button until you get to 18.
5. Then push the Start button (front of the coin door) until the other number goes to 3. That will turn on all sound.

I have also attached the backglass setup photo.
Alltek Centaur Game Settings DIP (resized).jpgAlltek Centaur DIP (resized).jpgAlltek solenoid board (resized).jpgnew Alltek boards (resized).jpgsounds (resized).jpg

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