Bally Centaur - flickering controlled lamps - not the usual cause

AlanJ

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I have my centaur working fine with either an alltek MPU board or an original -35 MPU board from another machine. But when I plug in the original -35 MPU board, it all works apart from a lot/all? the controlled lamps flicker quickly. (both on the main lamp driver board and on the aux lamp driver board).

The lamps are LED's and I've installed the LED flicker fix kit to the main lamp driver board - so it's not the usual led flicker issue..

Given it all works fine with either of the other MPU boards, it's a problem with this MPU board itself.

I'm suspecting some sort of timing issue, so looking at the circuit and components around the 555 timer, and the zero crossing circuit - with the hex invertor 4049 ic?

Am I on the right lines?

Anyone had this same issue before please?

Many thanks,
Alan
 

Sven Normansson

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does it flicker if you replace with incandescents? If it does then its a board fault, if it doesn't I'd suspect the lamp driver or aux lamp driver board.
 
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AlanJ

AlanJ

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does it flicker if you replace with incandescents? If it does then its a board fault, if it doesn't I'd suspect the lamp driver or aux lamp driver board.

it doesn’t flicker if i use the other mpu boards i mentioned above, so it’s deffo this mpu board that is at fault


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AlanJ

AlanJ

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swapped to other centaur and same issue. that 2nd centaur still has incandescent lamps. so deffo a mpu board issue.


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Pick Holder

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Good call @Sven Normansson

But Alan - at least you have an Altek to get it running that will be a lot more reliable long term. I think I would always prefer one of those in a game than an original board.

I know Mark Squires likes to repair faults like this :) give him a shout but when when a new altek is sub £200 it is not really good economical practise.

Depends if you are a purist.
 
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AlanJ

AlanJ

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Yes it's properly earthed.

Been reading up and studying the circuit diagram, got a theory, but will have to wait now - School run, dad taxi, cooking kids teas and all the crap for a few hours.......
 
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astyy

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Yeah, this thread is an interesting read. Out of interest which non-flicker solution have you implemented on the lamp board (and aux)?

A non-issue for me though as I prefer incandescents as the Bally God intended :p
 
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AlanJ

AlanJ

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Found this gem:

"f your Bally game is running very slow (solenoid pulses are delayed and long, controlled lamps flicker, scoring takes a few seconds to register) or if your game boots with the typical 7 LED flashes but then crashes (dead game with garbage on the displays), before attract mode starts you may have a bad C16 capacitor. C16 controls the display interrupt speed. If it is out of spec, it could cause the gap between display interrupts to be too small, leaving the processor no time to service other game operation. C16 is in the corrosion area near the 555 timer."

I dont have all these symptoms, just the flickering controlled lamps and also I have had a few occasions where the MPU resets after the 7th LED flash........ Hmm time to go capacitor hunting.
 
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AlanJ

AlanJ

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C16 looks ok. It checks out at 0.1uf - well its 0.103 to be exact. I'm gonna replace it anyway.

To test it I had to cut a leg off. I did this whilst the machine was switched on - and hey presto, the flickering controlled lamps problem stopped immediately, but of course other problems were created in turn - the score displays no longer work correctly - all linked to the NE555 timer circuit that C16 is crucial to.

The machine wont boot - gets to 5 flashes then sits there, reconnecting the cap allows it to boot and then disconnecting it after is ok. All makes sense, looks like the 6th flash needs the 555 timer circuit to be switching.

Im not sure Im on the right track here. But now need to find a new non electrolytic 0.1 uf capacitor.....bog std value but I seem to have every other value except this one!.


Did some more digging:
"Seven Flashes Constantly Repeats.
The MPU boots and gets to the 7th flash, then start all over and repeats the seven flashes, then starts all over and does it over and over. This can happen from a bad 6810 RAM at U7. Or possibly a bad socket at U7."

I have swapped the U7 Chip for one from another board, no difference, checked all the sockets are properly connected to the pcb - all test out ok, so doesn't look like it's that either.

Brings me back to the NE555 timer part of the circuit:
1606937880382.png
There are a few other components I can check out - those resistors. Could be the 555 chip is bad too, but the score displays were working ok before, suggesting it's ok - so im thinking more like a timing issue, which is controlled by the relationship between C16, R21 and R22 , I'll check those R's out
 
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AlanJ

AlanJ

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Got a load of parts and rebuilt the reset circuit and replaced other parts recommended by the pinwiki and the other great bally repair guide. The machine now boots, but sill occasionally getting a reboot. This isn't caused by the reset circuit as I've used my logic probe to prove it's not triggering a reset.

But the issue with the flickering lights is till there. A post on pinside has been helpful, the guy eventually found the problem - a bad via connection, so I checked mine and it's ok. It's some sort of weird timing issue. I might replace U15 as that was contributing to his problem, but then again looking at the schematic, I'm not sure why I should replace it.

I've done so much to the board now that it's probably about time to abandon it and just buy a new one. I was doing this more for the hell of it, and to learn, I have certainly done that!

I was going to order a new alltek board but find that the pinballdisplays website is not working! https://www.pinballdisplays.co.uk/

May as well do a load more testing tonight to see if I can figure out what the heck is going wrong. A helpful chap on pinside has given me some stuff to go measure with a logic probe.
 
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AlanJ

AlanJ

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Decided the best way to fix this board is build a test rig so i can measure and test all the signals on the bench

so built a quick power supply to give out 5v , 12v and 21.5v. this is all that’s needed to boot a bally mpu board and get all 7 led flashes.




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