TECH TIPS (EARLY BALLY).
BALLY
POWER DISTRIBUTION
The most common
question concerning the Bally 6800 games (Freedom thru Cybernaut) is
the one that deals with a no-start or locked up MPU. With the Power
Distribution chart and following text, it should be a snap to nail
down EXACTLY where the problem is.
Always check the end of the line first, in this case, the MPU. The
MPU has some really simple power requirements in order to run. It
must have a clean 5VDC (TP5) and an unregulated 12VDC (TP2). There
is a 43VDC in the mix but for now, we will concentrate on the other
two.
If the LED is lit but board is dead, it can be safely assumed that
the 12VDC is present because that’s what fires the LED. Check the
5VDC at TP5 next and if it is present (4.9-5VDC), the MPU is locked
up and needs work. But many times, the 12VDC or the 5VDC will be
absent or low and now you will have to determine why.
If the LED is not lit, check TP2 for a reading. If the 12VDC is
there, but LED is out, cross the legs (on right side) of Q2 with a
small screwdriver. This should turn on the LED. If it doesn’t,
assume that the LED is bad and replace it.
If the 12VDC is missing from TP2 on the MPU then forget about the
LED for now and drop back to the Power Supply for some voltage
checks. At the Power Supply, check for the 12VDC at TP3. If it is
absent, check the fuse at F3. Remove the 4Amp slo-blo and ohm it
out. Even if it looks ok, it can be open internally. If it ohms ok
then reinstall it AFTER you have squeezed the fuse clips together to
make for better contact.
If you still can’t find the 12VDC at TP3 after checking the fuse
then only two things remain to check. Find E11 and E12 test points
on the Power Supply. These are the two AC inputs to this circuit and
should read about 12VAC between them. If they are open then the
transformer winding is open also. If the 12VAC is present at E11 and
E12, then the only other item in the circuit is the Bridge Rectifier
(BR2).
These can be verified in circuit with the check Diode function of
your VOM. It is possible to have one or both sides bad on these
rectifiers. Replace it, if found to be open, and go back to the
original voltage checks on the Power Supply. If the rectifier were
shorted internally, the fuse would have blown as soon as the game
was turned on. It can happen either way.
Now you have the 12VDC at TP3 on the Power Supply but not at the
MPU! What gives? More than likely it is ONE wire causing the
problem. Looking at J3 of the Power Supply, find pin #8 (16 gauge
Orange wire). It is probably burnt and has shut down the
distribution of the 12VDC. Remove the terminal from the connector
and clean it, along with pin #8 of J3. If the connector terminal in
J3 has been heated too many times, it will have lost its tension and
will need to be replaced.
Let’s follow this 12VDC (Orange wire) and see where it travels.
After leaving the Power supply, it goes directly to the Solenoid
Driver where it goes in at Pin 12 of J3. It also makes a U turn and
heads out Pin 11 of J3 over to the MPU. Meanwhile, back at the
Solenoid Driver,
This 12VDC heads to the 5Volt regulator but makes an important side trip.
Just before it enters the 5Volt regulator, that really big Capacitor
(C23) in the middle of the board treats the raw 12VDC to a little
smoothing out.
A
closer look at this regulator and how it is wired into this circuit
will help explain some of the strange quirks that can occur. If the
5VDC goes out of regulation, (reads below 5Volts), it can be assumed
that it is somehow the Capacitor at fault. This may not be the case
at all. The Capacitor is wired in circuit with its Positive side
across the unregulated 12VDC, as you would expect. It is the
Negative side that can cause the problems.
Bally chose to keep the Negative side, (that goes back to the Power
Supply), a separate wire- independent of other ground circuits.
Even though
all grounds end up at the same spot, this independent wire helped to
keep noise down on the system. It also can lead to some weird
problems like shutting down the MPU or causing massive resets.
This single (white/brown) return wire heads out of the Solenoid
Driver from pin #10 of J3. It goes to the Power Supply and into Pin#
17 at J3. You may discover that these pin designations at the Power
supply are not the same as you’re game and in most cases it doesn’t
matter. The grouping of the pins of J3 allow for swapping around of
(Ground) wires between pins 1 thru 4 and pins 14 thru 20 of J3.
These are all ground returns and over the years, the wires could
have been moved around within these groups.
The important thing to remember here is that if this ground return
wire from the Capacitor to the Power Supply gets interrupted
for any reason; it will shut down the 5 Volt regulators and the MPU.
The fastest way to do a check on this Capacitor ground is to jump
the left (negative) side of the cap to any ground in the backbox. If
the game comes up, you have found the problem and tracing the
wht/brn wire back thru the system will find the disconnect.
At this point you have the 12VDC and the 5VDC both back and the MPU
has responded with its flicker/ flash routine except for the final
(7th) flash. Looking at the drawing again, locate R113 down next to
J4 connector. With your VOM on DC, check the left side if this
resistor for a 43VDC reading. If it is missing, (and there is no
evidence of a burnt connector at J4), then proceed back to the Power
supply for a check of TP5. If the 43VDC is missing then look at the
Bridge rectifier at BR3 after checking F4 and the AC inputs at E3
and E4.
When the 43VDC has been restored, go back to the MPU and recheck the
voltages at both side of R113. As the diagram shows, the left side
should read 43VDC and the right side should be 22VDC. If the left
side is ok but 22VDC is absent, change R113 (2K 1/4 Watt) resistor.
This article was aimed at the Power Supply system used before Xenon
(the games that had the Power Supply in the backbox). But it can
also be applied to the later systems, especially when testing the
12VDC and 5VDC Circuits of the Solenoid Driver and MPU. Different
wire colors may be found in newer games but the Test Points and
voltage readings are constant.
FAQ:
COILS ARE DEAD ON MY BALLY PINBALL GAME
Some of the
coils in my game have stopped working. Should I send you the
Solenoid Driver Board for repair?
If all of the coils have stopped working, look at the power supply
diagram. The test point 5 should register 43 VDC. If it doesn’t,
check fuse at F4. Remove it from the PC board and ohm it out. If it
checks ok, before putting it back, squeeze the fuse clips together.
At this point, is a safe assumption that the lack of 43 VDC is due
to a failed bridge rectifier (BR3).
If the 43VDC is found at TP5 then move down to J1 and look for 43
VDC at pin 6. This is a brown wire in Bally games and goes directly
to the playfield flipper coils. Locate this brown wire at one of the
flipper coils and measure for 43 VDC. If it is present at pin 6 of
J1 but not at any of the flipper coils, and then the problem is in
the wiring between J1 and the coils.
Other possible problems are shown on the Troubleshooting Flow Chart.
The 43VDC has been known to disappear on the early A8 sound board
(used on games Lost World thru Dolly Parton). This sound board used
43VDC to make 12VDC with a very crude voltage divider/regulator
System that would short the 43VDC to ground when it failed. When you
are trying to locate an erratic 43VDC problem in a game using this
type of A8 soundboard, disconnect the power to the board, as a
starting point for troubleshooting.
If the 43VDC is missing from the whole system, then the MPU will not
complete its 7th flash on self-test. This can be verified by
checking for 43VDC on the left side of R113 (located below and to
the right of the J4 connector). If the 43VDC is present on the left
side of R113 but there is no reading on the right side, then replace
R113 (2K 1/4 W). If BOTH sides of R113 read 43VDC then the board is
probably acid damaged and the whole area should be cleaned up and
components replaced.
I
think this subject has been thoroughly covered here and with the
troubleshooting flow chart; you should be able to determine the
exact location of your problem with “some/all coils not working”.