the classic reset problem
here's some of it:
3d. When things don't work: Game Resets (Bridge Rectifiers and Diodes)
What is a 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.)
Why are Resets so Common on WPC and WPC-S games?
I get this question a lot. "Why don't I have this reset problem on my Williams System11 games?" When WPC was designed they decided to use a voltage watchdog device, which was not implemented on earlier board designs. This 3-legged transistor-looking MC34064 device is on the CPU board at U10. (With pin1=output reset voltage, pin2=input supply voltage, pin3=gnd, and
could be replaced with a TO-92 case Dallas DS1811-10 with a 4.35 volt reset, but not suggested.) Williams did this to "micro-manage" the voltage to the CPU board. The new parts implemented on WPC (ASIC chip, which replaced the six PIA chips on system11), requires a consistent 5 volt power source. Their fear was without a solid 5 volt power source, sparatic behavior
could result, causing game and coil lock ups. Of course the downside to this is, as WPC games get older, reset problems become much more common.
Check the Easy Stuff First.
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.
+18 volts DC (lamp matrix): TP8 (TP102 on WPC95). This is an unregulated voltage, so it can vary from 16 to 20 volts. If this is low, check bridge BR1 and capacitor C6/C7 (diodes D11-D14 and caps C11/C12 on WPC95).
+12 volts DC regulated: TP3 (TP100 on WPC95). Should be 11 to 13 volts DC. This voltage comes from the +18 volts lamp matrix (discussed above), and goes through a 12 volt regulator (7812) and some 1N4004 diodes and an LM339 chip. If the +18 volts is correct at TP8 (TP102 on WPC95), but this voltage is low, it is usually the 7812 voltage regulator at Q2 has failed.