Whirlwind Pinball Machine

I think System 11 machines offer the best bang-for-the-buck as far as pinball
machines go. I think Whirlwind is one of the best.  I was happy to find one in excellent condition.

The topper is one of the most noticeable features: a fan that blows
on you during certain parts of play.

Shopped playfield.  The condition of this playfield was very good,
and did not need much work.  Very little paint wear, and inserts are level.

Audio Output for a Subwoofer
I have found that all pins can use enhanced bass.  This can be done by adding a internal amplifier (such as on my IJ), or by increasing the gain on the cab speaker (TOTAN, MM), or by using an external powered sub (Space Shuttle).  By coincidence, the Whirlwind ended up next to the Space Shuttle, so I decided to use the same powered sub. 

To enable this, I installed a mini audio jack in the same location as the Space Shuttle.   This was in one of the holes of the cab speaker grill.  The output jack is simply wired to the cabinet speaker terminals.

The output audio jack installed in the location with the most clearance
in the speaker cone - just off center.

The powered subwoofer accepts a Left and a Right channel input.  I simply connected one pinball machine to Right, and the other to Left.  The two audio streams are mixed together and sent to the sub.  The end result was very satisfying.  When the machine now speaks "Whirlwind" in that lowwww tone, it sounds very good.  The thunder booms also sound much fuller without being loud.

The two pinball machines that use the subwoofer. 

Making protectors
There are several places where the plastics were broken on the Whirlwind.  As with my other machines, I made protectors for those locations out of Lexan. 

This plastic is often broken on the right hand side in this image.  I made
a protector for that side, and the side over the scoop (left).

Although not broken, I also made protectors for the long thin plastics
on either side of the up/down ramp.  Someone sent me a picture
of his Whirlwind that had one of these broken into half, so
I figured that it was worth it.

The other places where I made protectors are not shown, but they include the upper corner of the plastic that holds the right red flasher, and the slings.  When I purchased these, I appeared to have obtained the last that Bay Area Amusement had.  When I checked the next week, they all showed out of stock.

Front cabinet damage repair
There was a hole in the front of the cabinet that was repaired with epoxy.  The artwork was restored with acrylic paint and waterslide graphics.

Original state of hole near "Start" button.

The hole was repaired by filling it with epoxy using a small mixing stick as the aplicator.  As the material started to slump, I quickly put a piece of clear tape on the lower half of the hole as a form.  I then continued to fill the hole, and finished it with a second piece covering the open area.  The result was a nice, flat repair with no sanding needed.

Hole repaired and printing replaced.

I then used acrylic paint to fill in the orange and yellow parts.  The yellow was "Ceramcoat Bright Yellow", and the orange was "Decoart Pumpkin Orange".  I have used these paints before on other Williams cabs, and the color match is perfect.

Finally, I photographed the area, and used Photoshop to extract the black, and filled in the missing text.  I then printed the art onto a piece of waterslide paper, and applied the "art" lettering.  The result is not perfect, but pretty good.  It is not noticeably different when viewed casually.

Power-up Knock
On a few occasions (once every 10-20 times), when I power-up the machine, the knocker in the backbox makes a loud "Clack".  This is a fairly common occurrence with System 11 machines, so I decided to investigate this.  Note that this knock occurs as soon as the power switch is flipped, and way before the CPU board boots up.  Thus it is not related to a diagnostic code report from the CPU board.

Scope trace of the knock.
Channel 1 (yellow): AC line @ F4 fuse.
Channel 2 (blue): Solenoid B+.
Channel 3 (pink):CPU 5V supply.
Channel 4 (green): Q23 base.
The knock occurs during the long high pulse of the green line.

The scope plot above shows the occurrence of the knock on power-up.  The key is the pulse on the green line, which is the voltage on the base of the Q23 Darlington driver transistor. When this is above about 1.2V, there is enough base drive to forward bias the transistor, and the Solenoid B+ (blue) dives down as the coil fires.  At some point, the CPU's supply voltage rises above about 2.25V, the green pulse is then shut off, and the coil releases.  The solenoid B+ does not recover until the other half wave (positive on fuse F5) charges the supply back up.

When we look at the driver circuit below, we see why this is happening.  As the CPU's 5V rises, U19 has not powered up yet, and does not ground its output.  As a result, the 560 Ohm pull-up,  and the  Q19 predriver, apply enough voltage to turn on Q23.  It is only when the 5V rises above about 2.25V that U19 wakes up and pulls its output low.  At that point, the knock is terminated.

The driver for the knocker on Whirlwind is Solenoid 6.

Note that there is a short pulse on the green line during the inital rise of the 5V in the figure before.  This occurs on every driver transistor in addition to Solenoid 6, and is when the 5V supply briefly passes through the region of 1.75V to 2.25V.  See a clean example below.  Thus the conclusion is that all solenoids receive a short (1 millisecond) pulse of current,  but this is too brief to activate the knocker, and we do not hear anything.  As for the long pulse, this is only noticed on the knocker due to two reasons: 1) the knocker's plunger is not restricted by any mechanisms, and 2) the knocker's plunger is activating a sounding device.

A clean power-up without the knock.  Note that there is still a brief pulse
on the base drive, and this occurs on all the drivers on every power-up.

So why does the second long pulse (and the resulting knock) only occur seldomly?  Refer to the scope trace image of the knock above.  There is a 'pause' in the rise of the CPU's 5V.  This pauses stretches the time that the driver circuit spends in the 'On' zone.  The reason lies in the way the 5V regulator is powered on the supply board.  As shown below, the voltage regulator (IC1) is powered from a half wave rectifier formed by D1 and D5.  If the machine is powered up when only a small amount of energy is remaining on the half wave, the rise of the supply is suspended until the next half wave of the AC line.  If this rise is suspended when the CPU's supply voltage is in the magical 1.75V to 2.25V range, there will be a long period when the driver transistor is enabled, and you get a loud "Clack".

Regulator of the CPU's 5V supply.  It is powered by D1 as the rectifier.

I repeated this test on my Space Shuttle (System 9), since it has the same design for the Solenoid drivers and power supply.  Sure enough, just as on System 11, all solenoids have a brief pulse on them.  However, this machine does not have a knocker, and I was not able to get a suspension of the power supply rise in the magical zone.  However, the design of the power supply board is a different revision, and the loads are different on System 9.

How to prevent this knock?  The best way is to have a rapid and uninterrupted rise in the power supply.  However, that may not be practical.  Another way is to put a capacitor in the driver circuit to absorb this pulse.  If the capacitor is put at the output of U19, it would have to be 10uF to produce a 5 msec time constant.  However, the current pulse into U19 when it turns on may affect its long term reliability.  Ideally, there would be a series resistor in the output of U19 to prevent stress.  Another location is on the emitter of Q19, however the circuit impedances are 10x lower there.  So we would need to increase the capacitor to 100uF for the same time constant.  This represents a similar reliability problem for Q19, and is also not desirable.  In the end, it may be best to just live with the problem with the knowledge of exactly what is occurring.



  • 5/2/09 - Purchased machine from Dan Heatherly.
  • 5/24/09 - Electronics repair.  There were only two items that needed fixing.  We now play and enjoy the machine.
    • The first was that the left flipper was weak.  This was repaired by replacing the left flipper coil. 
    • The second issue was with the upper display bank.  Segment 'e' was dark.  Tracing the problem, I found that R27 was bad.  Replacing this 10k resistor remedied the problem.  These are normally $120 each.
  • 6/8/09 - I took two days to do shop job of the top of the machine.  Except for removing the mylar, and clearcoating, everything else was performed.  Mods added were the powered sub and protectors.
  • 6/13/09 - Repaired hole in front panel near start button.
  • 2/20/10 - Investigated power on knock.

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(c) 2009 Edward Cheung