Quoted from Silverballwizard:I did the coil test and all coils pop except that one. I paused the test on that coil and nothing.....
I paused the test on other coils and they repeatedly fire.
what does that point to?
I don't have a logic probe....can a DMM do the test?
So, to summarize, neither the MPU nor the Pop Bumper Skirt Switch are able to fire the coil, but grounding Q73 tab, does fire the coil.
To me, that points to either U45 or Q72. The Ground from the Pop Bumper Switch and the Data signal from the MPU go through a NOR gate (U45). That signal then turns on Q72, which in turn, turns on Q73. Without a logic probe, it's difficult to know for certain. A logic probe will show you the brief pulse from the MPU in coil test mode, that will be difficult to see on a meter, because the signal is rapid, and by the time the meter responds, it's gone. However, we may be able to use the fact that these coils are specials to our advantage. Because the MPU changes the signal rapidly, BUT, the pop bumper skirt switch will be there as long as you hold it in. Normally, in game play, the switch activates, the coil stays on as long as the switch is made, but the pumper pushes the ball off the switch rapidly, so the coil is released.
Here's what you can do, but I don't know if you can get your physical leads of your meter in place well enough to test.
I've attached a diagram of the pre-driver transistor for reference.
With the game on and in a state that the OTHER pop bumpers work (we're going to use them as our reference), do the following. First test, that the working pop bumper works by pressing down the bumper skirt. Then remove Fuse F2 (power to the coil), and retest, making sure the pop bumper doesn't work now (going by memory here, you might have to experiment to find the actual fuse. Also, opening the coin door might do the same, but I don't recall on HS). What we are after, is that the logic works, but we remove the power to the coil so it doesn't fire while testing. Any fuse removal, do with game powered off.
Once you have the game to a state that the pops would work, but the power is removed, we're going to test the logic circuits.
Meter on VDC, black lead to ground. With the WORKING Pop Bumper (Let's choose upper Left Q77/Q76 pair) not made, put your red lead on each leg of the pre-driver transistor Q76 and record the voltage. You'll see something between millivolts and 5V on each test.
Working Pop Bumper OFF Leg 1 Q76 = X Volts
Working Pop Bumper OFF Leg 2 Q76 = X Volts
Working Pop Bumper OFF Leg 3 Q76 = X Volts
Now, put something on the Pop Bumper skirt to make the switch. Keep it held down for the next tests:
Working Pop Bumper ON Leg 1 Q76 = X Volts
Working Pop Bumper ON Leg 2 Q76 = X Volts
Working Pop Bumper ON Leg 3 Q76 = X Volts
So that's are reference. We're now going to compare to the non working Bumper
Non Working Pop Bumper OFF Leg 1 Q72 = X Volts
Non Working Pop Bumper OFF Leg 2 Q72 = X Volts
Non Working Pop Bumper OFF Leg 3 Q72 = X Volts
Now, put something on the Pop Bumper skirt to make the switch. Keep it held down for the next tests:
Non Working Pop Bumper ON Leg 1 Q72 = X Volts
Non Working Pop Bumper ON Leg 2 Q72 = X Volts
Non Working Pop Bumper ON Leg 3 Q72 = X Volts
You might have to use a paper clip tied to your meter lead to get to the legs....OR, if you are comfortable reading a schematic, there are points that are easier to reach. I've attached the schematic, so for example, to get to leg 2 of Q72, you see that is connected to Resistor R106. One side of R106 is connected to 5V (that's the little triangle), so visually look at the board trace to see which side you should measure on R106 to check leg 2 of Q72. Likewise, leg 1 can be measured at R105, and leg 3 at R107.
2n4401-transistor-pinout-equivalent (resized).pngSchematic (resized).jpg