I recently picked up a SS with a non-working Spider. I was surprised to find so little out there to describe how this works. After a lot of digging and probing with my O-scope, I got the creepy crawler spinning and thought I would pass on some of what I found that might help a fellow out that finds himself in a similar situation.

Notes: The motor is a stepper motor, driven by 4 wires. Two wires drive one coil, and the other two drive the second coil. The resistance of the coils on my stepper are approx. 35 ohms each.

The schematic for the stepper driver motor is not included in operator manual. This is reported to have been distributed in an update from Bally. The board is very simple. It takes 12v and regulates it down to 9 volts to drive the stepper motor. (The motor I have is rated at 12v, so it is not running at full torque).

Two solenoid drivers (39 and 40) are used to send step signals to the board. These do nothing more than pull down a resistor, so it is a bit of overkill. Don't anticipate any problems with the drivers being overstressed, but you could still see bad connections preventing this signals from reaching the stepper board.

The two above signals are buffered and inverted to drive transistor pairs that route the 9V to the coils. Each coil can be biased in either direction based on the control signals. To check the operation, run the "wheel" diagnostic and observe a square wave as pulses are sent to the motor. The sequencing of the pulses cause the motor to move in a clockwise direction. The plastic hub that fits on the motor has an interrupter 1/2 way around to trigger the opto sensor. The CPU sends out pulses until the opto changes state to establish where the wheel is pointing. From there, the CPU sends pulses to point where it wants to go. If you manually send pulses to the board using the diagnostics, you see low-low, high-high, low-low etc. at each input to the motor for each step. The manual steps will count up to 200, which is 360 degrees since the stepper is a standard 1.8 degree per step device.

If all the pulses and power looks good, and the opto is changing when the wheel spins, it's time to look at the motor. Are the coils open? If they measure 35 ohms, then its time to take the motor apart. 4 screws hold it together. Look for varnish flaking off and jamming the stator grooves. Wire brush with a soft brass brush, and blow out with an air gun. does the motor spin free? If the bearings seem tight, give them some Teflon spray lube, and see if that frees up everything. Time to put it back together and see if it works. If not, new motors can be found on the web for as little as $15 if you want to connect your own connector, or less than $100 for something similar to NOS.

Other notes: To get the motor off of the back box, you have to release a set screw on the shaft. Remove the 3 light unit above the motor assembly so you can get at it. It will take a long 1/16 inch Allen wrench to reach the screw which will be in a brass insert on the plastic shaft cover. Reverse this to put it back. Make sure the spider's back legs are positioned towards the rear of the spider to balance the weight out on the shaft, and all legs clear the surface. Don't over tighten the set-screw, but do use some Loctite (NOT superglue).

Hope this helps somebody out there.

Mac

Thanks for the kind words. I've decided to strip the playfield, remove all the dinged up Mylar, repair the spider hole, and do an automotive clear coat on it. Also going to have a go at flame polishing the ramps. Those ramps are a pain to get off. I'll post some pictures as I find time. I've think I have too many restorations going at once (a TZ, Space Shuttle, Road Show, and now this Scared Stiff). Waiting in line is a Black Knight and Firepower. Yowza...

...If I followed the OP well, there are two solenoid drivers (Q39 and Q40) controlling the steps for movement? Though it's stated that these are hardly under any load, could one of them still be defective causing the motor to have a locked torque, or should I look elsewhere?
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Also relevant, we seem to have problem with our crate lock post. Both high and hold power do not work. The coil resistance checks out fine, the playfield and powerboard connection seem okay. Could both high and low driver transistors have failed?
Many thanks for any solutions and suggestions.

Might be good time to take a close look at your power source for all of those drivers... could be a common source of the problems.

Adding some detail I looked up from someone doing troubleshooting on this topic. Thought it best to keep this information together, so adding to this thread.

The spider motor driver signals referred to as Q39 and Q40 originate on the A-20028 Power Driver Board. They are latched in a 74LS374 U4 pins 9 and 12. They are then double buffered with ULN2903 and exit U3 from pins 11 and 13, then route out to the J110-4 and J110-5 connector. This connector is the small one, 3rd from the left on the bottom. Yel-Wht and Grn-Wht wires are typical.

I have also added a clip of part of a service bulletin relative to this topic.

Hope this helps. Mac

Interface (resized).JPG

Service Bulliton (resized).jpg

Glad to help you out.

Mac