Gottlieb System 1 technology



System 1 was Gottliebs first series of solid state pinballs. They were made in years 1978-1980. The series consists of familiar 16 machines Cleopatra, Sinbad, Joker Poker, Dragon, Solar Ride, Countdown, Close Encounters, Charlie's Angels, Pinball Pool, Totem, Incredible Hulk, Genie, Buck Rogers, Torch, Roller Disco and Asteroid Annie. Up until Charlie's Angels there was also an EM version made of these games. Asteroid Annie differs from others, being a single player game which was probably made to use up System 1 leftover parts from storage.

The System 1 technology is simple. Gottlieb did not use electronics to create anything that couldn't have been done with EM technology. There are three circuit boards in backbox: power supply, CPU and a driver board. Additionally there is a sound board in the lower cabinet in later games.

Score and credits were shown in easy to read big blue fluorescent displays. There were no dot matrix displays in these games.

These repair tips assume that you have a schematic of at least one of these machines. If you haven't, no problem - you can download them later on this page.

Player's point of view

The playfield is very similar to the last EM playfields. Gameplaying happens in one level with no ramps or rails. There are 2-4 flippers, usually two slingshots, and some bumpers. Occasionally an eject hole and droptargets. You can get a picture of how simple the games were, by thinking that the System 1 driver board could control just eight solenoids - of which the sound controls, knocker and outhole already took 5 in every game! What was left to use in playfield were whopping 3 controlled solenoids, although some games used some of the 36 lamp drivers to control additional solenoids. Bumpers and slingshots worked directly by their own switch and did not need driver board control. The three solenoid could be used for example for two eject holes and a droptarget bank reset. Like EM-machines, these were simple games but still required skill and concentration. I would say that most of the System 1 games were surprisingly interesting to play.


In the three first Sys 1 games there was a three tone chime unit, like in EM games, in cabinet. That changed in Close Encounters to a simple tone generator. Major improvement in sounds came with Totem, when System 1 got a microprocessor controlled soundcard to replace the previous 3-tone beeper. Both the chime box and the sound cards were located in the same place, in the right side of cabinet.

Power supply board

Schematic diagram

System 1 power supply gets juice directly from transformer at the bottom of cabinet. It consists of rectifiers and regulators to create the various output voltages of +5V, -12V, +8V, +4V, +60V and +42V - pretty many different outputs. The power supply has three main blocks. One takes in 69 VAC and outputs +60V and +42V voltages, the other works on 2x11.5 VAC and generates +8V, +5V and +4V, the third takes 2x14 VAC and makes -12V.

60V / 42V

60V is used to power score displays. The smaller credit display works on 42 volts. Both voltages are done in the power supply from 69 VAC. The input voltage is rectified by diodes CR6-CR9 and filtered with capacitor C6. Series transistor Q2 regulates the output voltage with the help from Q4 and zener diode CR11. Current limiting is done with Q3 and R13. The output voltage can be adjusted to 60V exact with trimmer potentiometer R16. A 18V zener diode CR12 is used to drop the 60V to 42V for credit display.

5V / -12V

5V and -12V voltages are needed on CPU board. 2x11.5VAC from transformer is rectified by CR1 and CR2 and then filtered with C1. Good old 723 regulator and series pass transistor Q1 form a 5 volt regulator, whose output can be adjusted with trimmer R4. Current limiting is done with sense resistor R1A.

The negative voltage -12V is done by rectifying transformers 2x14VAC with diodes CR3 ja CR4, after which C4 filters it. Commonly used 7912 regulator gives without any other tricks a current limited -12V output.

Display filament bias voltage +8V (score displays) is done with a 8.2 V zener CR21 and resistor R21 from the same voltage used to generate +5V. Credit displays bias voltage +4V is made with two series diodes CR22 and CR23 from the +5V output.

Protective circuits

To prevent overvoltages at the CPU board, both +5V and -12V outputs are equipped with protection circuit made of thyristors SCR101 and SCR201 and zeners CR101 and CR201. If the output voltage rises over zener voltages (5.6V and 13V) the thyristor fires and shorts the output, causing the fuse to blow.


System 1 power supply is a fairly robust device. A small problem is heating of the +5V series transistor Q1, which makes the whole board to get quite warm because it is attached to Q1's heatsink. This eventually causes the filter capacitors to dry out. A dried out capacitor in 5V or -12V voltages can cause strange problems and game lockups. Improper filtering of 60V display voltage can cause the displays to flicker or go dim. Sometimes even the Q1 can fail, original PMD12K40 transistor is hard to find but a more common replacement is MJ1000. This is a 60V / 8A NPN darlington. After years, also the trimmer potentiometers begin to fail because of dust, causing overvoltage protection to trip or other problems. The trimmers can be cleaned with contact cleaner or preferably replace them with new ones. Rectifier diodes CR1 and CR2 are underrated in some oldest boards. It is good to replace those with at least 4A diodes.

A special failure possibility in these boards is misconnection of connector J1. The connector is removed when backbox is taken off, and when replacing it is possible for the connector to go in upside down! There is a 'this side up' sticker but it may have been lost during the years. Pay attention, an upside down J1 connector makes ugly things for the power supply board.

Driver board

Component placement
Schematic diagram


Most of the components in driver board are related to lamp control. IC's Z1-Z9 and transistors Q1-Q24, Q33-Q44 and related components control 36 lamps. The lamps are controlled in groups of 4 with 74175 (4 bit latch) TTL IC, which driver MPSA13 transistors. Unlike newer machines, lamp driving is not multiplexed matrix. The CPU drives the 4 bit latches by setting correct data to lines LD1-LD4 and then strobes one of the 9 latches with a pulse on one of the DS1-DS9 signals. The 4 bit patterns stays at latch output and the 4 related lamps until a new one is set. There are two relays, TILT and GAME OVER, that are controlled by lamp drivers, with transistors Q1 and Q2.

If a 74175 fails totally, it causes four lamps to stop working. Those lamps can then stay always on or off, depending on failure mode. If a driver transistor fails, it affects only one lamp at a time. Often a good way to check TTL circuits is to measure with multimeters diode test range between its output and ground. The threshold voltage shown should be approximately same in all outputs. Exact value is not important. Of course this measurement should be done with power off! If one output shows different value, it is a good sign of chip failure. More brightly burning lamp is a sign of driver transistor failure. The transistors damage easily if lamp driver output gets shorted either by faulty lamp or by faulty lamp socket. From the game manual you can find out which transistor controls which lamp. Often not all lamp outputs are in use. It is possible to save on repair costs by taking the unused driver transistors to replace burned ones. Note that this means that the board will not work in another game any more...


System 1 driver board can control 8 solenoids. Control is done in a very simple way. The CPU board outputs a TTL level control signal via diode to driver transistors base, causing the coil at transistor collector to operate. Solenoid #8 is handled with two transistors in Darlington connection. It can be a heavier type, typically for droptarget bank reset. The diodes protect CPU board in fault situations, preventing coil voltage from entering CPU board. Again, you can use unused solenoid driver transistors to replace burned out ones.

A common problem in System 1 games is in solenoid control. The ground connections between CPU, driver and solenoids are not very solid. This can cause ground potential to rise and solenoid driver transistors to continually conduct. Transistors and coils then overheat and fail. To fix, make sure that all ground connections are good and clean. You can also make better grounds with heavier cable soldered directly to boards. Bad grounds can also cause lamps to glow all time at half brightness.


Component placement
Schematic diagram part 1
Schematic diagram part 2
Schematic diagram part 3

System 1 CPU board is built around Rockwell's 4-bit PPS4/1 microprocessor and its support chips. These chips are nowadays almost impossible to find, so it is best to hope these won't fail. However, if this should happen, your game is not trashed yet. There are at least two modern replacements available, the Ni-Wumph CPU board fits all System 1 games, and a PI-1 board by Pascal Janin has even more features than the original, such as attract mode, high score table, etc, etc!

Battery problems

The Rockwell special IC's do not fail very often. Instead, the CPU boards often get damaged by the bookkeeping memory NiCd battery soldered onboard. The original batteries last long, even 10 years. Unfortunately these games are almost 25 years old! Aging battery will leak caustic substance that destroys circuit board and components. If you get a CPU board that has the original battery in place, do not wait, act now! Remove the battery and throw it away. Attach some wires to a new 3.6V battery. Solder the wires to CPU board and mount the battery at a place where its leaking will not cause board damage.

If the worst has happened, first remove the leaking battery from the board. Then try cleaning the board with vinegar and toothbrush. Flush with clean water. After cleaning, check if there is foil damage and replace damaged foils with thin wire. Badly corroded components must be replaced. Of course it is impossible to find replacement Rockwell chips. Just try cleaning and resoldering the pins. All this is tedious job and takes a lot of time. But you might get the board working again.

Solenoid control

As explained in driver board section, it has diodes to prevent solenoid voltages from CPU board. Anyway if that somehow happens, expect damage in Z6 or Z7, the 7417 inverters driving the driver board. These are easy to replace, so don't panic yet... but if the Rockwell IC U4 happens to go at the same time then you are in trouble. Try finding a spare board with working U4, or go for the Ni-Wumph or PI-1.

Switch matrix

The playfield switches are read with U5, luckily again there are some cheap inverters between this IC and the playfield, namely Z8 (7404) and Z9 (7405). When several switches stop working at a same time, you should begin troubleshooting from these two chips. Again the multimeters diode test range can be useful. Measure the threshold voltage (with power off!) of every Z8 output and Z9 input. If you find one that differs from the others, replace the chip.

Display control

The displays are controlled by U6, with a few TTL IC's. 7-segment decoders Z16 and Z17 take care that the numbers shown look correct - if the displayed numbers look strange then one of these is probably gone. Z16 controls player 1 and 2 displays and the credit display, while Z17 handles player 3 and 4 displays. On score display driving there is a small circuit that makes number 1 to be shown with an extra eighth segment in the middle of the digit instead of the usual two right side segments. This is done with gates Z13/Z14/Z15. Suspect those if there are problems in showing number 1. The displays are multiplexed, meaning one digit at a time is shown. Digit selection signals come from gates Z18..Z21.

A sure way to damage CPU boards display driver parts is to remove or replace display tube with power on. A bone headed repairman such as myself learned that only after trying twice. No need for others to try that anymore!

Lamp control

As explained, the driver board uses signals LD1-LD4 and strobes DS1-DS9 for lamp control. These come from Rockwell chip U3 via inverters Z24..Z26. If you have lamp problems that do not com from driver board you can try replacing these inverters. It is possible for also Z30 (74154) to fail and stop outputting DS signals although the inverter chips are OK.

More schematics

Bottom board schematic
Bottom board and light box schematic
Light box cabling
Block cable diagram
Example of playfield illumination
Example of playfield solenoids
Example of switch matrix


Normal operation sequence at power on is: displays are blank for 5 seconds, after which both T and Q (TILT and GAME OVER) relays pull in for a moment and the displays start showing zeros. A common System 1 fault is that the 5 second delay is missing, displays come on at once and the machine is inoperative. This is usually caused by bad SLAM switch connection. There is on inside front door and one at the ball roll assembly at left side of cabinet. Both these must be normally closed. Similar problems can also be caused by coin switch shorting to front door. There must be an intact insulator between coin switch leaf and actuating wireform.

All Gottlieb System 1 boards are interchangeable between games. The only parts that change is the game personality PROM on the CPU board, and a similar PROM on the (newer only) sound board. The prom chips are labeled in different games as follows:

A or 409 Cleopatra
B Sinbad
C Joker Poker
D Dragon
E Solar Ride
F Countdown
G Close Encounters
H Charlie's Angels
I Pinball Pool
J Totem
K Hulk
L Genie
N Buck Rogers
P Torch
R Roller Disco
S Asteroid Annie & The Aliens

The sound prom has text "SND" with the game letter.

Older sound board

Schematic diagram

Close Encounters was the first game to use this simple tone generator board. Three oscillators made with 555 timers generate three different tone frequencies. These oscillators are switched on by signals from driver board. Low tone for 1000 points, middle tone for 100 points and high tone for 10 points, just like with the chimes before. Tones are amplified with an LM380 that drives a speaker at bottom of cabinet. The board has its own power supply, that takes 24V solenoid voltage and generates about 12VDC with a 13 volt zener and TIP31 transistor. This board seldom fails. Sometimes the power supply zener gets shorted, causing no sound. Once I have seen the TIP31 short, after which every IC on board will fail! Luckily they are inexpensive.

Newer sound board

Schematic diagram

Totem came with this all new and fine sound board. In this new board, sounds are generated with a D/A converter and a 8 bit microprocessor. The processor is much more powerful than the one on CPU board! Even though there are no more PPS4 special IC's on board, it has a Rockwell R6530 interface chip which has internal ROM to hold the sound board CPU software. Naturally these are getting hard to find. Rumours of a modern replacement are being heard. A common fault of these boards is capacitor C14, that is used with R14 and U6 to generate clock frequebcy for the board. When replacing C14, be sure that new cap is 10 pF 5%, a wrong value or improper tolerance will cause out of tune sounds! The only game specific part is bipolar prom U4. If you replace sound board with one from a different game, check that you use the correct prom for your game, or you will be playing with wrong sounds.


Mechanics is one area where Gottlieb was very succesful. So in System 1 machines there are very few mechanical troubles. Normal EOS switches in flippers require cleaning every now and then. Playfield parts are durable, only part I personally do not like is the flimsy plastic spinner used in some games. Even that has no problems with durability, it is just too light to keep spinning nice and long. Of course the normal problems with drop targets and rubber bands breaking happen. System 1 drop targets are still available. They are the same as in EM Gottliebs.

System 1 playfield is painted and lacquered in traditional EM style. At that time there was no Diamondplate or other such things. So the proper way to take care of playfield is to wax it after every few hundred games with good Carnauba wax. It is good to replace or at least turn the rubbers to new position when they show signs of wearing. System 1 games use WHITE rubbers, the black ones belong to newer games and are not bouncy enough for the shallow playfield angle. There are red rubbers on flippers.

DIP switch settings

There are 3 banks of eight switches each on the CPU board. They are used to set game pricing and other parameters. If your manual is lost, here's how to set the switches.

The first eight switches control pricing. There are four switches for each coin slot, so that the switches 1-4 control left side and switches 5-8 the right side slot:

1/5 2/6 3/7 4/8 coins credits note
off off off off 1 1
off off off on 1 2
off off on off 1 3
off off on on 1 4
off on off off 1 5
off on off on 1 6
off on on off 1 7
off on on on 1 8
on off off off 1 9
on off off on 2 1 No credits until 2nd coin dropped
on off on off 2 2 No credits until 2nd coin dropped
on off on on 2 3 No credits until 2nd coin dropped
on on off off 2 4 No credits until 2nd coin dropped
on on off on 2 5 No credits until 2nd coin dropped
on on on off 2 3 1 coin - 1 credit, 2 coins - 3 credits
on on on on 3 1 No credits until 3rd coin dropped

Switches 9-24:

Switch 9: on=3 balls per game, off=5 balls per game
Switch 10: match feature on/off
Switch 11: on=high score awards replay, off=extra ball
Switch 12: on=tilt penalty ball in play, off=game over
Switch 13: credits displayed on/off
Switch 14: game start sound on/off
Switch 15: not used
Switch 16: not used
Switch 17 and 18: maximum credits, off-off=5, off-on=8, on-off=10, on-on=15
Switch 19: on=switches 1-4 control both coin slots, off=left slot with 1-4, right with 5-8
Switch 20: sounds when scoring on/off
Switch 21: high game to date displayed on/off
Switch 22: high game to date awards 3 credits on/off
Switch 23: coin sound on/off
Switch 24: not used

Bookkeeping and tests

System 1 games keep audit counters of games played, replays etc data. Bookkeeping and test functions are available by pushing button inside front door once. Function number is the shown on credit display and corresponding value on player 1 display.

Function Value Note
0 Coins thru left slot If switch 19=on, this counts both coin slots
1 Coins thru right slot If switch 19=on, this is 0 and both slots are counted in Function 0
2 Total games played
3 Total replays
4 Number of times SLAM switch has opened
5 Total extra balls
6 Total tilts
7 First high score level 0=not used
8 Second high score level 0=not used
9 Third high score level 0=not used
10 High game to date score
11 Display test: 1. and 3. player displays count 000000-999999 If the test button is not pressed within two cycles, test ends.
12 Display test: 2. and 4. player displays count 000000-999999 If the test button is not pressed within two cycles, test ends.
13 Lamp and solenoid test. All lamps light for 5 seconds, then all solenoids operate in sequence. Closed playfield switch numbers are shown on ball in play display, if any.

Pushing the test button moves on to the next function. If the button is not pushed in one minute, the game returns to Game Over state. Bookkeeping values can be cleared by pushing RESET button on CPU board at desired function. After that the zero value must be entered in memory by pushing test button once more. High score levels at steps 7-9 can be changed by holding down the start button. Value increments then by 10000's. At desired level push the test button to enter new value in memory. The value van be cleared by RESET button on CPU board. Zero at high score level means the level is not in use. But in high game to date score the zero does not disable it!

If the game has been in storage long and the battery has drained, the bookkeeping may be incorrect or even show misformed digits. This can be corrected by clearing every value and then setting reasonable levels to high scores and high game to date.

Troubleshooting and fixing

What's where in a System 1 game

What to do when a System 1 game fails? First, try to locate the problem. Is it the CPU board, the driver or power supply? Most System 1 problems are caused by bad connectors. The board edge connectors oxidize and the Molex connectors lose their tension. Cleaning and slightly bending the pins may help for a while, but it is best to replace every connector, if you want your game to operate trouble free for years.

At power on, all displays are blank, and nothing should happen in 5 seconds. Then the two relays on playfield click and all score displays show zeroes. If this happens, there are probably no major faults in CPU board or power supply.

Game does not boot up.

If the CPU board does not boot as described, first check that the operating voltages are OK. They should be checked at the CPU board, across capacitors C16 and C17. These caps are near the power connector. Across C16 there should be 5 V, and across C17 there should be 12 V. If these voltages are incorrect, there are problems with power supply board or the CPU board power cable. See the description of power supply earlier on this page. Note that the +60 V and +42 V output voltages have a different ground pin on the power supply board than all other voltages. You will get very strange results when measuring voltage against wrong ground.

A common problem, that prevents the CPU from starting, is an open SLAM switch. There is one switch on the game front door, and another on the ball roll assembly at left side of cabinet, that open if the game is slammed or lifted so that the ball rolls to the end of its track. It can happen that either of these switches is open because of oxidization or misadjustment. Then the 5 second delay at power on does not occur, instead all displays show zero right at power on, and may flicker. Remember that normally the SLAM switch contact points should be closed, i.e. touching each other.

Front door SLAM switch. Note contact points should be closed.

There are at least two TILT switches in every game, that shouldn't be mixed with SLAM switches. TILT switches are normally open. The pendulum must not touch the ring around it, and the playfield vibration switch blades must not touch each other.

Ball roll SLAM switch (normally closed) and playfield TILT switch (normally open).

SLAM switches are closed and the game still doesn't start. What's the problem?

Again, bad connector is the first suspect. Slam switch connects thru connector J6 on CPU board. If that is loose, the game may think it is in slam condition. Permanent cure is to jumper IC Z29 pin 3 to ground (pin 7 of same chip) or short the capacitor C2.

Location of C2 and Z29 on the CPU board.

OK, you fixed the slam switches and the game still does not start up correctly. The RESET signal may be missing. It is generated by Z2, the 4528 monostable. You should first replace the capacitors C31 and C32 (0.1 uF), they do sometimes fail. The circuit generates RESET signal to the CPU, and prevents CMOS RAM writing at startup. You could check operation by measuring voltage at pins 7 and 9 of Z2, they should both go high (+5 V) after about one second of power on. The CPU's RESET signal can be checked at the test connector TC1 pin 14, which should be at -12V at startup, and the after one second or so, rise to +5V level. If this does not happen, check Q5/Z2/Q6.

Note that the pushbutton on CPU board marked RESET does not generate the reset signal in any way. It is used only to reset bookkeeping values.

The two white caps near Z2 can fail.

Gottlieb revised the RESET circuitry a bit during Sys 1 production. The new version gives a longer RESET pulse, and ensures the CMOS RAM is locked out quickly at power off. Older boards can be upgraded as follows:

RESET signal is OK, SLAM switch is closed and yet the game does not start.

This is unusual. Maybe one of Rockwell chips U1-U6 is faulty, but you should check the clock frequency. At the test connector TC2 pins 11 and 12 there should be about 200 kHz and 365 kHz. If these are missing, replace crystal Y1, a 3.579 MHz "color TV" crystal. They can go bad.

Test connectors TC1 and TC2.

Still doesn't work.

Bad thing. The problem must be in the Rockwell chipset U1-U6, that can't be obtained anymore. You could swap chips from another board, but I would recommend going to the Ni-Wumph or PI-1. Replacing the quad-in-line packaged chips while trying to keep the board and spare chips intact is not easy. And the replacement CPU boards are not terribly expensive.

The bookkeeping values are held in CMOS RAM powered by a small nicad battery mounted on CPU board. The battery can leak, destroying circuit board or components. If your CPU board has battery "acid" (actually the stuff oozing out of nicad is not acid but base) damage, it must first be cleaned and possibly broken traces fixed. Not an easy job.

Game starts but one or more solenoids are continuously on.

Driver board transistors solenoid assignment.

Do not keep power on for more than 30 seconds if a solenoid is constantly on, to prevent coil and driver transistor overheating.

First check for shorted solenoid driver transistor on driver board. Turn power off, remove connectors from driver board and test continuity between middle and right legs of solenoid driver transistor. There should be infinite resistance. A shorted transistor usually shows zero ohms. Solenoids #6 - #8 are the game specific playfield solenoids. Note that solenoid #8 is controlled by a heavier transistor. It can drive big coils such as a target bank reset solenoid. Because the design only allows 3 controlled solenoids on playfield, some games use lamp drivers to control more solenoids. Because lamp drivers only control 6 volts and solenoids operate on 24 V, there is a transistor mounted underside of playfield, usually near the controlled coil. Check your game manual to find out if your game uses this arrangement.

If many or all solenoids are constantly on or solenoids do not work at all, the problem is usually missing -12V voltage at CPU board. Check the voltage across capacitor C17. If it is OK, the problem is probably in buffers Z6 and Z7 (7417).

Solenoid buffers Z6 and Z7.

Some lamps always on or off.

The lamps are controlled in groups of 4. If a 74175 latch in driver board fails, one lamp group will misbehave. Check your game manual for lamp assignments. If a single lamp is constantly on or off, then its driver transistor is probably bad. Lamp driver transistors are in one long row at the center of the driver board. You really need the manual to find out which transistor controls a certain lamp.

74175 lamp controllers.

Displays do not work.

If all displays are totally blank, you probably have a power supply failure or short somewhere. First check the 1/4 A fuse on cabinet bottom board. If it is open, do not replace with a bigger fuse! There is a problem somewhere.

The player score displays operate on 60 V, and the smaller credit/ball in play display uses 42 V. If the 60 V is bad missing then also the 42 V will be bad. First check that the voltages are correct at the power supply P3 connector (pin 5 is ground, pin 1 is 60 V, pin 3 is 42 V) with the cable removed. A bad display module can bring the voltage down, so if the power supply looks good with P3 cable off, try unplugging one display at a time and see which is the bad one. Remember to turn power off before plugging or unplugging any connector!

If the displays light up, but show incorrect numbers or are partly blank, again try unplugging one display at a time to find out if any display has shorts. The problem may also be in CPU board. 7-segment decoders Z16 and Z17 supply the segment data to the displays. Player score displays have an extra vertical segment in the middle of each digit, to show "1" properly centered. Gates Z13-Z15 are used to detect the number 1 and disable the decoder while feeding the extra segment. Credit display does not have the extra segment. Gates Z18-Z21 drive the display digits. If one ore more digits are always blank, suspect these chips.

Playfield illumination is always off.

Check fuses on cabinet bottom board. Also, playfield lights are controlled by the T (tilt) relay, mounted on playfield underside. The relay pulls in when game is tilted. It is normally off. There are one set of contact points on relay to turn off playfield lights in tilt, and another pair to disable flippers, bumpers and slingshots. The other relay, Q, is the game over relay. It pulls in during game and also enables playfield solenoids. The backbox "ball in play" and "match" lights are alternated by Q relay.

Q and T relays.

My game does strange things.

The game starts and plays correctly but sometimes locks up or resets, or scores incorrectly. Guess what. Check the connectors! Also, if your power supply still has the original electrolytic capacitors, it is now time to at least replace C1, which filters the main 5V voltage. If your displays flicker, replace also C6.

Unusual or erratic operation especially after game has been on for long time, might be caused by overheating game PROM Z23. The bipolar PROM gets quite hot, and more than once I have seen a game doing very strange things because of a hot PROM. I always attach a small heat sink to the PROM with some superglue. This cools things down and fixes the heat problem. And since the game PROMs are hard to find, it is also a good idea to lengthen its lifetime even if you dont have problems. It seems that some PROM chips are more sensitive to heat than others, but a sure thing is that high temperature will shorten an electronic components life.

Some solenoids or driver board transistors get very hot.

Gottlieb System 1 games suffer from grounding problems. The solenoid ground can rise above logic ground, causing driver transistors to be more or less conducting continuously. Solenoids may work but get stuck or overheat. To fix, make sure that all grounds are properly equalised by adding ground wires from every board to backbox metal panel. On the power supply board, solder the wire to negative side of C1. On the CPU board, solder the wire to negative side of C16. And on the driver board, connect the ground wire to negative terminal of C1. Attach the other ends of the three wires under a backbox panel mounting screw.

Newer style sound board keeps blowing its chips.

The +5 V voltage for the sound board comes from an onboard TO3-cased 7805 regulator. The regulators ground connection is via two zinc plated mounting screws. These can corrode, causing the ground connection to be intermittent and what's worse, the regulator output voltage can rise to +12 V!

Sound board with the big regulator at top center.

This will be very bad for the logic chips, and often the 6530 RIOT will then get shorted, bringing down the voltage and hopefully saving the other chips. But since the 6530 contains masked ROM, it is unique for this board and not easily found anymore.

So before your sound board goes "Poof", check and clean the regulator mounting hardware! Put some protective grease on the surfaces before reassembling, to prevent moisture causing any corrosion and blowing up the hard to get chips.

Thanks for the tip, Dwight!

Replay scores cannot be set, or game allows only one credit.

Replay scores and bookkeeping values are stored in CMOS RAM Z22. The problem may be in this chip, but before replacing it check capacitor C2 (220 pF) on power supply board. Fault in this capacitor causes noise in +5V supply voltage, which may prevent the CMOS RAM operation. Also, check or replace C24 (0.01 uF) on CPU board. Sometimes also the 4081 chip Z1 can be faulty, keeping the CMOS RAM disabled. Try replacing Z1 if the capacitors and RAM itself are OK and it still doesn't work.

Thanks for the tip, BB!

Game starts, gives ball to shooter and freezes.

This happens when the game PROM is missing or incorrectly seated. A little bit of contact spray to Z23 socket may help. Also check resistors R122-R131.

I replaced faulty U4 or U5 on CPU board, with known good chip and it does not work.

These two chips contain the game operating system ROM, and must be of the same revision. The revision levels that work together are:

U4                U5
1753CC works with 1752CD
1753CE works with 1752CF
1753EE works with 1752EF

System 1 faults are usually easy to diagnose and fix, because the problems are usually in power supply or simple TTL chip faults. Sometimes however a Rockwell special chip can fail, making repair very difficult. Fortunately there are already two manufacturers making replacement CPU boards. And remember that most problems are caused by bad connectors. Chances are your circuit boards are all OK.

Thanks to Pekka for pictures.
Schematic diagrams (c) Gottlieb.