(Topic ID: 238837)

Bally-35 MPU all pf switches not functioning


By Pinballer73

60 days ago



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  • 19 posts
  • 6 Pinsiders participating
  • Latest reply 41 days ago by Eric_S
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#1 60 days ago

Trying to help a friend get his Bally Playboy up and running again. The game presented in a non working state, 5 LED flashes. Tested all voltage test points on the MPU and all were well within range. Removed the MPU and installed an Alltek, powered on and game booted and played. Left my friend to enjoy playing his game and took the MPU home to investigate.

The history I received was that it had been working for quite a while and then the pf switches didn't register and the sound went funny, not playing all tunes. Eventually it wouldn't boot and that was how I found it. The battery had been removed long ago and replaced with a lithium coin cell. The board had some sockets replaced previous on the memory IC's and the CPU. The CPU itself has no markings whatsoever, wiped clean or sanded off. I replaced the sockets for the EPROMs and the CPU as these were still the originals. Also removed U12 (555), installed a socket and put in new ICs at U10, 11 and 12. Both PIA's and the 555. Installed back into the game and the board boots, start a game, beauty. Well not so fast, not one switch matrix switch on the playfield registers. Connectors J2 and J4 are both clean and pins soldered in place.

I've checked over the board thoroughly and checked continuity from each pin of J2 to U10 and from J10 to the CPU at U9, along with component values, all test ok.

I could replace the PIA at U10 and test, but my gut feel is something else is wrong. The sounds isn't right either and that is controlled by the other PIA at U11. However, the pop bumpers, flippers, slingshots and ball trough kickout work fine at power on/ball on the playfield. With the voltages and resistance to ground connections checking out, I'm at a loss to workout whatelse is common?

Is it possible that the CPU chip is the wrong type? But the board now boots ok and so I'm told the game was working. Any ideas? Hoping someone can help or seen this problem before.

Forgot to mention...when in switch test it reports a flashing zero indicating no switches are closed, which isn't surprising considering none of them register during game play.

#2 60 days ago
Quoted from Pinballer73:

Is it possible that the CPU chip is the wrong type? But the board now boots ok and so I'm told the game was working.

^This rules out a wrong IC. It's pretty much impossible for the board to work correctly with a wrong IC, and then suddenly not work because of it. Something has failed.

Quoted from Pinballer73:

Bally-35 MPU all pf switches not functioning....However, the pop bumpers, flippers, slingshots and ball trough kickout work fine at power on/ball on the playfield.

Hmmmm. Double check against the switch matrix diagram. Cross off all switches on the diagram that are not working.

35switch (resized).jpg
#3 60 days ago

Thanks for the reply. Absolutely none of the playfield switch matrix switches register a score with the original board installed. With Alltek board installed the game functions as it should.

#4 60 days ago
Quoted from Pinballer73:

Thanks for the reply. Absolutely none of the playfield switch matrix switches register a score with the original board installed. With Alltek board installed the game functions as it should.

You're welcome. I'd start with replacing PIA U10 like you suggested earlier. It's really the most logical move at this point.

#5 60 days ago

There is no single component after U10 that could cause this. The simplest test is swap U10 and U11 and see if the problem moves to the sound and solenoids

Update: I thought I saw this somewhere. On the old pin repair guide it mentioned that a bad diode on a dip switch can cause havoc on the switch matrix. The test for this is turn all dips off to remove them from the circuit.

#6 60 days ago
Quoted from Cheddar:

The test for this is turn all dips off to remove them from the circuit.

Good point.

#7 60 days ago

Thanks for the tips. Just switched all the DIPs off and check each diode with a meter, unfortunately they all test ok. I guess I'll have to replace the PIA. It just doesn't make sense that the board exhibits all the same faults as before with 2 new PIA's installed. Should I go ahead and replace them again, or is there something else I should check first?

#8 60 days ago

I missed where you replaced both PIAs. Looking at the schematic it's hard to imagine that you'd have a deeper issue with U10 that wouldn't prevent a boot as well. That said maybe it is one of these lines:

IRQ U9-4 - U10-37&38
R/W U9-34 - U10-21

Make sure you have 5VDC on pin 20 and Ground on pin 1 of U10. Finally I'd run through all the data lines between the 2 sockets and check continuity. Finally make sure none of the pins on either socket are shorted to the one next to them.

I had an issue with a non booting board due to the solder on the component side of the board for a socket touching a trace that ran between the pads.

2 weeks later
#9 42 days ago
Quoted from Cheddar:

I missed where you replaced both PIAs. Looking at the schematic it's hard to imagine that you'd have a deeper issue with U10 that wouldn't prevent a boot as well. That said maybe it is one of these lines:
IRQ U9-4 - U10-37&38
R/W U9-34 - U10-21
Make sure you have 5VDC on pin 20 and Ground on pin 1 of U10. Finally I'd run through all the data lines between the 2 sockets and check continuity. Finally make sure none of the pins on either socket are shorted to the one next to them.
I had an issue with a non booting board due to the solder on the component side of the board for a socket touching a trace that ran between the pads.

Thanks Cheddar. I spent some more time working on this today and can offer some further information. Just to recap, with an Alltek board installed the game functions perfectly.

With the original MPU re-installed (see above for the work done to it) I noticed today when methodically working my way through each playfield switch, some switches do register with the original board installed. However a large number of switches don't work and a few solenoids don't fire.

The working switches and solenoids are listed as follows:-

Switches 6, 8, 22, 23, 24, 31, 32, 39 & 40 all register.

Solenoids 1, 4 & 5 work, along with the flippers.

All the other switches and solenoids don't work. With all the DIP switches in the off position on the MPU board, then tested for continuity from the header pins of J2 through to the U10 PIA. Swapped U10 and U11 with the same issues. Installed new PIA's, same issues still exist. I'm lost as what to try next. Any ideas would be greatly appreciated.

#10 42 days ago
Quoted from Pinballer73:

I'm lost as what to try next. Any ideas would be greatly appreciated.

This is the problem with the shotgun approach to repair. You can guess, and each time you do it lengthens the process and increases frustration. The problem might not even be a faulty component. There could be shorts or opens in connections between components not revealed in a visual inspection. The best way to locate the problem (or problems) would be to examine the signals and operation with the board in the operating state using oscilloscope or logic probe.

#11 42 days ago
Quoted from wayout440:

This is the problem with the shotgun approach to repair. You can guess, and each time you do it lengthens the process and increases frustration. The problem might not even be a faulty component. There could be shorts or opens in connections between components not revealed in a visual inspection. The best way to locate the problem (or problems) would be to examine the signals and operation with the board in the operating state using oscilloscope or logic probe.

Whilst I agree, the shotgun approach isn't always a good solution, I just can't understand whatelse could cause this issue as there is so few components involved. Especially components common to the inputs. Hopefully someone will see something I've missed.

#12 42 days ago

Just a thought... Have you reflowed the pins on the MPU connectors? Just because the plugs are good, doesn't mean the pins might have cracked solder joints. Very common with these old Ballys, and that would explain everything or at least a lot. One bad joint on one switch matrix return can wreak havoc.

Shawn

#13 42 days ago

Amongst the repairs you mentioned in your first post you replaced both PIA chips. Did you prove whether either of the original PIAs were faulty?
What frequencies are you measuring for the display and zero crossing interrupts at pin 40 of U11 and pin 18 of U10 respectively?

If the board ever had any battery corrosion, post some clear pictures so we can see how extensive it became.

Quoted from Pinballer73:

The working switches and solenoids are listed as follows:-

Switches 6, 8, 22, 23, 24, 31, 32, 39 & 40 all register.

So switches on return lines I5, I6 and I7 are generally working. At the J2 pin header on the MPU board, what happens if you directly jumper a wire from any switch strobe line (say strobe #0 at pin 1) to any switch return lines: I0, I1, I2, I3 and I4 (pins 8, 9, 10, 11 and 12 respectively)? Does switch test mode register anything?

#14 42 days ago

Until it's daylight here, these are the best pictures I can manage. Will update with better pics in the morning.

20190408_030522 (resized).jpg20190408_030605 (resized).jpg
#15 42 days ago
Quoted from Pinballer73:

Will update with better pics in the morning.

Cheers, yeah if you can take pictures outdoors when it's daylight (but in shade so there's no shadows) they'll come up much clearer. Those preliminary pics show the board generally looks in decent shape.

#16 42 days ago
Quoted from Quench:

Amongst the repairs you mentioned in your first post you replaced both PIA chips. Did you prove whether either of the original PIAs were faulty?

No, as wayout440 stated, I followed the shotgun repair method approach.

Quoted from Quench:

What frequencies are you measuring for the display and zero crossing interrupts at pin 40 of U11 and pin 18 of U10 respectively?

Haven't had an oscilloscope handy to test this. Is there any other way?

Quoted from Quench:

So switches on return lines I5, I6 and I7 are generally working. At the J2 pin header on the MPU board, what happens if you directly jumper a wire from any switch strobe line (say strobe #0 at pin 1) to any switch return lines: I0, I1, I2, I3 and I4 (pins 8, 9, 10, 11 and 12 respectively)? Does switch test mode register anything?

I will try this next chance I get. All pins on J2 test ok for continuity back to U10.

#17 42 days ago
Quoted from Mk1Mod0:

Just a thought... Have you reflowed the pins on the MPU connectors? Just because the plugs are good, doesn't mean the pins might have cracked solder joints. Very common with these old Ballys, and that would explain everything or at least a lot. One bad joint on one switch matrix return can wreak havoc.
Shawn

No, however it appears someone else has previously. All pins at J2 test ok for continuity back to U10.

#18 42 days ago

What a difference some daylight brings, much better photos.

20190408_081757 (resized).jpg20190408_081823 (resized).jpg

#19 41 days ago

I recently ran into odd behavior on my HG and it ended up being a bad 5101 RAM chip. The MPU booted properly, but lamps weren't acting right. Try a NVRAM or a different 5101. Otherwise, it looks like you replaced the IC sockets. Did you verify continuity for all of the address and data lines? Maybe check for short circuits between the pads; it is very easy to create a solder jumper and ohming out all of pins is the only way to check for any inadvertent shorts.

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