does it come back on (reset)
"Game resets are probably the biggest problem with 1990 to 1995 WPC to WPC-S games (and to a much lesser extent, WPC-95 games). The pinball will seemingly shut off, then power back on (like the game was turned off and back on quickly). Typically, this will happen during game play, when the flippers are used. If the +5 volts (which powers all the logic circuits) dips momentarily below 4.7 volts (from heavy voltage draw when the 50 volt flippers are used), the "watchdog" circuit chip on the CPU board resets the CPU, momentarily shutting the game down. The high current draw flippers stresses the 5 volt power components in the system. If these 5 volt power components are starting to fail, the +5 volts dips, and the watchdog circuit
resets the game. When the game shuts down, the power components under stress are relieved. Then the voltage returns to +5 volts, and the game powers back up. This reset process can happen anytime, but usually happens during game play. (When things are really bad, sometimes the game won't even power-up, as it gets into a loop of turning itself off and on.)
Proper AC Wall Voltage?
Important: Before starting to dig in and try to diagnose the bridge rectifiers, set the DMM to AC Voltage and test the wall socket voltage. Make sure there is 115 to 120 volts AC present! If there is only 112 volts, this can cause the game to reset. Some games, like Twilight Zone, will often reset if the wall voltage is below 117 volts.
This problem happens mostly in the summer, when household power consumption is at a high, or if the game is plugged into the same circuit as another high power device (air conditioner, refrigerator, etc). WPC pinball games draw a maximum of 8 amps of power. Most home circuits are 15 amps, so two pinballs on one circuit should be the maximum. Also don't have the game plugged into the same circuit as another power sucking device (like a dehumidifier, sump pump, air conditioner, refrigerator, etc.) If the problem is persistent, the game can be re-jumpered for low-line voltage, or the driver board modified to bump up the 5 volt power to 5.1 volts (this is described at the end of this section, and really are 'last resort' things).
Check the Driver Board Voltages.
Next make sure the voltages at the driver board are Ok. Of course this assumes the wall voltage is Ok (if the wall voltage is low, any unregulated voltage will certainly be low, and often regulated voltages will be low too). Here's what to check ("TP" means Test Point, which are test points on the driver board). Check these voltages with the game on, and in "attract"
mode. Remember there is more information on voltages in part one of this document.
+5 volts DC: TP2 (TP101 on WPC95). Should be 4.92 to 5.1 volts DC. If this is below 4.92 volts, the game will most certainly reset easily, as this is the voltage the "reset watchdog" examines. Often the problem is bridge rectifier BR2 (diodes D7-D10 on WPC95) and the related filter capacitor C5 (C9 on WPC95). Sometimes it could also be the +5 volt voltage regulator
is failing (Q1 LM323K or LM317 on WPC95). Or it's very common for the input connector (J101 or J129 wpc95) or 5 volt to CPU board output connector (J114 or J101 wpc95) on the driver board. At this point do NOT remove/reseat the connectors!
This is very important. Removing or reseating the connectors will make finding the actual problem nearly impossible. So don't touch them yet!
Check for +5 volts on the CPU board. Yes I know, you checked the +5 on the driver board TP test point. But there are *two* connectors (or sometimes a third/fourth "Z" conector too) that go from the driver board to the CPU board. If these connector(s) are having problems, the +5 volts will be lower on the CPU board than it is on the driver board. The best place to test for +5 on the CPU board is right at the CPU board game EPROM pin 32 (the last pin). If the CPU board's +5 volts is even just a bit lower than the Driver board's Test Point +5 volts, that means the connector(s) between these two boards need to be re-pin'ed with new Trifurcon connector pins. This is very common and just re-pin'ing these two connectors can fix a lot of reset problems (without having to change any driver board parts).
Next reseat the right side driver board connectors J101. Power up and re-test the +5 volts on the driver board Test Point. If the voltage has gone up, then the input connector J101 is bad. Repin this connector with new Trifurcon connector pins. If it's the original connector (IDC), you will have to replace the connector housing too.
Recheck the voltage on the CPU board at the game ROM pin 32. Now reseat driver board connector J114 (J101 on wpc95) at the lower left. Recheck the CPU board +5 volts at game ROM pin 32. If the voltage has gone up, connector J114 needs to be replaced. Repeat this procedure for CPU board connector J210, and then repeat with the "Z" connector (if the game has one).
Again if voltage changes after a connector reseat, the connector MUST be repinned with new Trifurcon connector pins. (And wire brush the male connector pins or replace them too.)
If the CPU and Driver board +5 volts are very close to each other and are 4.92 volts DC or higher, try this. Remove driver board +5/12 volt connectors J114 (power to CPU board), J116 (cabinet), J117 (backbox), J118 (playfield), and measure the 5 volts at TP2 on the driver board (on WPC95 connectors J101, J139, J138, J140/J141 respectively). If you still below 4.92 volts, BR2/C5/C4/LM323K regulator are the likely culprits. If the +5 volts goes up with these four connectors removed, one of the other boards/devices is dragging the +5 volts down. Replace the connectors one at a time to try and find the culprit.
If any of the above voltages are low, resets can occur. But really the voltage that matters the most is the +5 volts. Again it must be 4.92 volts or higher for a game to not reset. Remember just because the above voltages are Ok, does *not* mean the game won't reset. Remember, the above voltages are being tested in attract mode, and not under stress.
Now it's time to check some more voltages, but under stress. This is a bit more difficult to do, but here is the procedure. Use a non-autoranging DMM (or set your auto ranging DMM to non-autorange). Or use a scope.
Check TP2 (+5 volts DC) on the power board. Try and get the game to reset and see if the +5 volts dips during the reset. There should be no change in the +5 volts, even during a reset.
Check TP4 on the power driver board, which is the zero cross signal. Again it should look steady with no changes even during a reset.
On the CPU board check U10 pin 1 (the reset pin on the MC34064). This pin may dip low during reset, forcing a game reset when the flipper buttons are pressed. The U10 is the watchdog circuit, and when it's reset pin 1 goes below 4.7 volts, the MC34064 forces the CPU to reset and reboot. You can follow the voltage trail back from the MC34064 and try and figure out
the exact component causing the problem. Remember if during the process a reset connector fixes the problem, this connector must be replaced (both header pins and terminal pins) to fully fix the problem.
But why is the voltage on U10 pin 1 dipping below 4.7 volts? There are a number of things that can cause this, as discussed here.
Check the Connectors (J101/J129, J102/J128, J114/J101, CPU J210, and Transformer).
First connector to check is input power J101 (J129 on WPC995) on the power driver board. This provide AC power from the transformer to the power driver board, which ultimately ends up as +5 volts DC, 18 volts DC unregulated, and +12 volts DC regulated (via bridge rectifier BR1 & BR2, some filter caps, and some voltage regulator circuits). If this connector is damaged
in any way, this can cause the voltages discussed above to be low, and resets to occur. Try a simple reset. If a "dark" game now boots or resets go away, replace the connector pins with Trifurcon style .156" pins, and replace the driver board pins with new .156" header pins.
Also check the connector that takes power out of the driver board and to the CPU board. This is connector J114 on WPC/WPC-S, or connector J101 on WPC-95.
Check the input power connector on the CPU board at J210. Also if there is a "Z" connector inline to connector J210, check that too.
Now try re-seating the connectors on the large transformer in the bottom of the cabinet. If there is any resistance in the transformer plugs, that can reduce the voltages going to the rest of the game. This only takes a moment to do, so it's not a bad thing to try.
Another bad connector could be J102 (J128 on WPC95) on the power driver board, 16 volts AC. Though less likely to be a problem, reseat it and see if resets change. Also check J112 (J127 on WPC-95), as this provides power from the transformer too (9.8 volts AC).
If the reset problem changes after reseating a connector, you have a TEMPORARY fix! Yes I did say temporary, as chances are excellent the reset problem will come back. The connector pins really need to be replaced to permanently fix this problem The only way to fix this properly is to replace (at minimum) the connector housing terminal pins (with Trifurcon pins),
and the circuit board header pins (but at dead minimum replace the terminal pins with Trifurcons). It is very common for these connectors to have bad pins or cracked solder joints, especially on Twilight Zone. Due to vibration and age, these connectors can just plain fail, and have some internal resistance. Again use Trifurcon style pins, which grab the male connector
pin on three sides (thus giving better contact and vibration resistance.)"