This pinball repair guide for System1 MPUs is just usuful for fast testing and frequently MPU defects; I will not talk about the background or special circuits. Two different versions of the MPU were produced. The main difference between Rev. A and Rev. B MPUs is the reset section, due to Rev. A MPUs have a general problem with booting and Gottlieb improved this circuit on their Rev B MPUs. If your MPU is equipped with a big black reset switch, you have a Rev A, Rev.B MPUs usually have a smaller red push button. Before you begin with MPU repair, please messure the voltages at TC2 between pin13 (GND) and pin14 / pin15. You should have 5V, at pin 14 and -12V at pin 15.

B) the reset push button:

Indeed, this push button has a reset function. But just to reset the bookkeeping values (highscores and such) and not to reset or test the MPU. (I have written another article about that, please search in section Flash.

C) the game doesn´t boot at all, but the general illumination is on:

It is hard to find a fully working sys1 game. "Pinball is working but has a small defect, super easy to repair for somebody with little knowledge " is a very common text at internet auctions for games with working general illumination but damaged circuit boards. Often that means, The MPU has to be repaired or sometimes be changed. The MPU´s chipset is a 4-bit system by Rockwell, the PPS4/2 series. These ICs are also called "spider-ICs" because of their strange legs and are not easy to get nowadays. The MPU won´t boot, if one of the spider IC is missing or not working. Fortunately, the spider ICs have little defects - you can also find them in 70s satellite command units. If the battery has leaked and the lower left side of the MPU is almost covered with grey crystals, do not even think about repairing your circuit board. You won´t be successful, because the A1752 spider IC is not longer available. Keep the MPU for parts - you might need them later!

D) the switch matrix (A1752 spider IC at U5)

The entrance and exit of the playfield and door switches is controlled by the A1752 spider IC, a 7405 (Z9), a 7404 (Z8) and another 7405 (Z28). If one of these ICs are bad, the game will not start. The switches are not protected against shorts or else to prevent MPU damage. No other company saved producing costs in such a stupid way. In case of a short, always the ICs next to the switch matrix are destroyed. The strobes are controlled by Z8, the returns by Z9. If the game stops working during a play, and isn´t restartable, change Z8. If a coil is constantly energized and the game does not boot, desolder one wire that is connected to the coil and change Z9. If Z9 has heavy burn marks, use your MPU as spare parts and save your repair time, because next in line, after the Z9, is the A1752 spider IC. You will not find them anymore. Usually, the connectors of the switch matrix have more or less corrosion. Check, that both connector and connector pins of the MPU has NO corrosion and clean them carefully! This is the most common cause, if your game doen´t come up. Do not use sprays and change the connectors or at least the bad pins.

E) MPU solenoid circuit (A1753 spider IC at U4)

The solenoids are driven by the A1753 spider IC. The IC is as like the A1752 spider IC, a Ram / Rom Combo IC with a special Gottlieb image, however this software is different from the A1752 spider IC. Important: You can use the following combinations for U4 and U5 - otherwise your MPU won´t boot.

Usually, the A1753 spider IC is working fine, if not, the game doesn´t start. If a coil is always energized, search for a faulty transitor at the solenoid and lamp driver combo at the beginnen. Read the document in section Flash. If you cannot find defect parts, you can do the following: Change one of the driving ICs U6 or U7 (both are 7417), or one of the resistor next to the ICs is toast. Usually, a leg of a resistor breaks on MPU, on which the battery has leaked. If so, replace all resistors. They are cheap and you have done a proper repair work.

F) MPU lamp circuit (10696 spider IC at U3)

Z24 (7404), Z25 (7404), Z26 (7416), Z27 (7405), Z29 (7405) and Z30 (74154) are responsible to drive the lamps. Moreover the reset button, the slam tilt switch and also the outhole switch are connected to the 10696 spider IC at U3 and Z29. If the 10696 spider IC has gone bad, your game doesn´t start and you cannot play pinball :(

G) the bookkeeping feature (10696 spider IC at U2)

The bookeeping feature is connected to the U2 spider IC. Z3 (4049), Z4 (4049) and Z5 (7405) are hex inverters to invert the incoming signals, Z22 is again the annoying 5101, a static ram where highscores, credits and such is stored. Replace it with an EEpromadapter and avoid buying new (old) 5101 ICs and batteries in the future (you can cut it off). You can find it in section Sandra. If the bookeeping function is out of order, check the connector and later the 5101. At least, you might change Z29. If the game doesn´t go into attract mode or you can see strange symbols on your displays that do not disappear by deleting all bookkeeping values (that is very important!!!), change the 5101. If the 10696 has a defect, the game doesn´t boot. There is also an overview about the bookeeping feature and the system1 MPU dip switch settings in section Flash.

H) MPU display circuit (10788 spider IC at U6)

All signals for the displays come from the 10788 keyboard and display adapter. If you have always the same segments, that do not work on both player 1 and 3 displays, replace Z16 (7448), if you have other strange behaviour on displays 1 and 3, check Z11 (7417). Equiv to player 1 and 3 check Z17 (7448) or Z12 (7417) for player 2 and 4. The 7408 ICs Z18-21 are responsible to drive the digits. Z18 and Z20 for player 1 and 3, Z21 and Z19 for player 2 and 4. If just one display has missing segments or digits, search on the display unit itself. The Gottlieb Futuba display has a quite unique segment called "h-segment" to display the "1". If the "1" doesn´t appear or you get strange symbols or nothing at all, replace Z13 (7404), Z14 (7404) und Z15 (7421).

I) CPU, reset and clock circuit (11660 spider IC at U1)

If the CPU doesn´t work correctly, the game - guess what - doesn´t boot. But before throwing the MPU away, check the reset and clock circuit of the 11660 spider IC. If your reset section or the clock circuit are damaged in any way, the CPU cannot run and you cannot play "Torch" for example. Messure the reset line with your DMM at test connector TC1 pin 14. If you have less or more than 5V +/- 5%, change the Z2 (4520) and the two capacitors C31 und C32 (both are 0,1uF). Check the clock signal at test connector TC2. If you have more or less than XXXX V at pin 11 and 12, replace the crystal Y1. Rev. A MPUs have sometimes problems with the reset - so take an eye on this circuit, if your game runs with a Rev. A module.

J) The PGOLProm (MMI 6351 IJ, position Z23)

The PGOLProm (Z23), PGOL=Pinball Game Oriented Language can make you really angry and is one of the most incompatible ICs I have ever seen. What a stupid idea, to use that IC. Gottlieb realized that very early, but used a similar biprom (NOT THE SAME!!) on their multimode sound module. Congratulations!! This IC contains special game data and differs from the 15 games Cleopatra to Asteroid Annie and the Aliens. Moreover this is the only difference on all system1 MPUs. If the game boots and goes into "attract mode" and you can start a new game, but neither points are added nor playfield lamps are driven (for example bonus lamps), this IC is bad. Or easily explained: With a defect Prom it is like playing a Gottlieb Black Hole with a Cleopatra prom or playing a Cleopatra with a Cleopatra Prom...think, that should be the same. I hope, you are imagining now, what I mean.

X) Where can I order the unique ICs??

It is very hard to find the Gottlieb spider ICs, however the 10696, the 11660 and the 10788 are still available in section Petra, if you search for something special, just send a short email.Also the TTL series become harder to get: You can also find 7404, 7405, 7416, 7417 and 7448 in section Petra, the EEpromadapter (5101 and battery replacement) and a replacment for the PGOLProm are available from Sandra.

© 2005 Nicole. Please report mistakes!!