Greetings from the PinWiz --  In response to Kelly Goodman's request
and to clarify the previous responses, the pinball stepping unit in
question is called a 'credit unit'.

It consists of a (ratchet or toothed) wheel with a step up solenoid and
a reset solenoid on a sheet metal frame.  The wheel usually has a drum
attached that shows the credits available.

There is a pin attached to the wheel at the zero credit position that
hits switches to open the circuit to the reset coil to make it stop at
zero and also break the circuit to the start button.

There is also an adjustable pin that can be moved to several preset
positions that opens the circuit to the step up coil and acts as a
limit on credits.  Usually the maximum credits are in the range of
20-40 credits.

The actual mechanism is somewhat complicated as there is a link from
the step up solenoid to a little catch, called a 'pawl' that engages
the wheel and pulls it in the up (or forward) direction when the
solenoid is engaged.  There is also a pawl on the frame that prevents
the backward (down) motion of the wheel.  From the reset solenoid comes
another link with pawl that pulls the wheel in the down direction and
also lifts the frame pawl so the wheel can go backwards.

The units made by all major manufacturers, Bally, Williams, and
especially Gottlieb, were all exceptionally well constructed and in all
the time I have been repairing pinball games (21 years) I have yet to
see one fail other than for coils or switches, or the occasional spring.

Unfortunately they, like so many other bits of past tech, are becoming
harder to find intact.  If the credit wheel display is not needed, a
pinball 'bonus unit' could also be used.  It usually would have only 16
or 21 positions and has a big rotary switch that could be used to
switch a lamp display of the credit amount.  The operation of the
mechanism is identical.

It needs only a transformer to provide power, typically a few amperes
at 28 or 48 volts, depending on the manufacturer.

If only 15 credits maximum were needed, it would be possible to make a
stepper circuit using available or surplus rotary steppers, which I
often see at surplus houses.  These only step in one direction but one
could use two in a chase type circuit to add and subtract credit.
Additional relays would be needed to provide some logic, and a more
complicated unregulated DC power supply would be needed.

There are also base 16 up-down counters available in TTL and CMOS ICs
which would require some circuit design, as extra logic and buffering
for the switches would be needed, as well as a regulated power supply.

Now, I know next to nothing about coin pianos, but I assume that either
they already have a cash box with a coin acceptor mechanism, or else one
would have to be added.  I believe that kits are available for kiddie
rides and such, that would provide a complete ready to install package,
although it would probably be ugly and expensive.

Obviously, any way one goes there is bound to be expense.  I would
be happy to discuss this with anyone in more detail.  If there were
actually a market for a mechanism like this, I might be persuaded to
design something.  I would guess an add-on unit could be used on any
type of player if appropriate controls could be devised.

Also I might suggest a note or call to Randy Fromm,
randy@randyfromm.com , ICQ# 10591073, who is one of the leading
amusement machine tech/tech trainers in the country.  He would know a
good source for old pinball parts I'm sure.  You can visit his web site
at http://randyfromm.com .

Bill Kibler - "the PinWiz"