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Electronic Troubleshooting

Rotation VIII Troubleshooting
(Getting your board to boot)

The following summary is intended to be a troubleshooting guide for the electronics in Midway’s Rotation VIII.

As you have probably already noticed, the circuit boards used in this machine are not used (to my knowledge anyway) in any other machine. As well, there are virtually no self-diagnostics available to help resolve machine electronic faults.

This guide assumes you have a reasonable understanding of electronic repair, have good soldering skills, can remove and replace components including DIP components, have basic electronic testing equipment and can read a schematic. An oscilloscope would be helpful, but a reasonable logic probe may still work.

Main Board

A little background on the main control board first. The main board is based on a Z-80 processor. The Z-80 processor uses separate pins for the address buss (16 lines) and the data buss (8 lines). This address and data buss all pass through to the daughter board which holds the 2716 style eproms and the NV memory. The daughter board also generates the RD (data read) signal used by a number of components on the main board.

Now, to add another level of complexity, the designer, I’m sure in his or her infinite wisdom, chose to use several additional components originally designed for the 8080 and Z-85 processors, and here is where the rub comes in. These two possessors used multiplexed data and address lines, in other works, the lower 8 address bits share the same lines as the 8 data bits. That means in addition to the 16 address lines and 8 data lines on the Z-80, you have another 8 other lines that can have data or address.

So, unless everything on the two separate address and data busses including the daughter board work, the main board will not boot. The main board is smart enough to send itself a reset pulse if it does not boot within a certain amount of time. Monitoring that reset line will give the trouble shooter an indication that the board is trying to boot, but is not successful. 

OK, have I scared you yet?

Having repaired a number of main boards, there are a couple of common faults that may be encountered. Before starting any diagnosis, I am assuming that all voltages have been checked, connectors are solid and all boards are in place. I’m also assuming the main board does not show corrosion damage.

Situation 1) Turn on machine and nothing happens, only GI lights come on, no table movement and no controlled lamps are lit.

Situation 2) Power on and random switched lights, solenoids and/or table movements and no start-up tune.

Situation 3) Power on, board boots and plays a tune, but as it boots, you get random solenoid firing.

Motor Driver Board

This board will commonly fail, usually when anything gets in the way of the rotating table. Wires, cables, almost anything can cause it and the fuse rarely protects it.
The good news is that this board is easily repaired. Usually what happens when one of the driver transistors fail is the table will turn in one direction only, cannot correct for an overshoot and will not start a game. Almost always, the failure will be one of the Darlington pair transistors, TIP 110 or TIP 115. All four are easy to replace and are commonly available.

Occasionally, if the Darlington transistor drivers are good and the table does not move, the problem may be in the large 3.3 ohm resistor. Check it for continuity. Rarely the LM3900 goes bad, but it can happen.

Last update January 7, 2015