Testing a Power Supply


Required:

Suggested:

The power supply board takes several AC inputs from the transformer, and outputs DC voltages to run the game from. If the power supply doesn't work, nothing works.

Before starting: Check the fuses. Use your meter, set to test continuity, and make sure that there is a "beep" from fuse clip to fuse clip across each fuse. Check to make sure that they are the correct ratings (1 Amp, 5 Amp, 15 Amp) as marked on the board.

Before starting 2: Disconnect CN2, CN3, CN4, and CN5 from the power supply. Leave CN1 connected.



Testing the AC inputs.
Set your meter to test AC voltages. If it is not an "auto ranging" meter, set it to the 200VAC range. It is rare to find a problem here, but it's still a good place to start testing. There are six pairs of wires in connector CN1. To test the input voltages, put the probes of the meter on each coloured pair (red shown) and verify that the AC input voltage is what it should be. The pairs are:
  • red / red
  • yellow / yellow
  • brown / brown
  • blue / blue
  • green / white
  • green / white
Testing the DC outputs.
Set your meter to test DC voltages. If it is not an "auto ranging" meter, set it to the 1000VDC range. Connect the black lead to TP8 (Ground)
Test Point 1: +170VDC
Touch the red probe to TP1 on the board. You should see a reading around 170V on your meter. This value need not be exact, it can be as low as 160V and will work fine. It may even be 172V or so. If you find 0V here, then the high voltage section of the power supply will need to be repaired. The other possibility is finding close to 230VDC here, also indicating a problem with the high voltage circuit.
Test Point 2: +12VDC
Touch the red probe to TP2 on the board (between the two large can-shaped capacitors). You should see a reading around 12VDC. This value also need not be exact, and is often around 15VDC.
Test Point 3: +5VDC (logic)
Touch the red probe to TP3 (above and to the left of the two large can-shaped capacitors). You should see a reading of about 5.8VDC. If the +12VDC at TP2 is missing, then this will also be wrong, as the +12V is fed through the 5V regulator RG1 to produce the +5V here.
Test Point 4: +5.6VDC (lamps)
Touch the red probe to TP4 (top lead of the resistor). You should see a reading around 5.6V. This is the switched lamp voltage supply, so the reading need not be exact, but is normally pretty close.
Test Point 5: +39VDC
Touch the red probe to TP5 (under the heatsink, top lead of the large cement resistor). You should see a reading around 39VDC. This is the solenoid voltage, so the value need not be exactly 39V, but is usually between 38-40VDC.
Test Point 6: -5VDC
Touch the red probe to TP6 (to the right of TP2). You should see a reading of -5V. Depending on your meter, it might be -4.8V or -4.9V, but it is normally very close to -5V.
Test Point 7: Logic
Assuming that the voltages at TP1...TP6 are good, the board is probably ok, but there is one remaining test point to check: TP7. The power supply has a voltage monitoring circuit that checks the output voltages and ensures that they are within reasonable tollerances. If one of them is found to be bad, the power supply will shut down the game to protect it. This also helps when the game is first turned on, to keep the processor from trying to start until the power supply output voltages have stabilized at the correct levels. A clue that there may be a problem here is finding the wire for this circuit between the Power Supply and CPU clipped. To test the output of the voltage monitor, use a logic probe (inexpensive Radio Shack logic probe shown). Connect the probe's ground lead to TP8, and use the probe tip to check TP7. If all is well, TP7 should be floating, so you will read no signal with the probe. This is OK.
Test Point 7: Logic Bad
Shown is the same test as above, but with the probe indicating a LOW signal at TP7 (the green LED is lit). This will keep the game from booting. If the voltages at TP1...TP6 are good, then there is a problem with the voltage monitor circuit itself.

Checking the power supply board only takes a couple of minutes with a meter. If all the test points are found to be correct, then it should be safe to connect up the CPU and the displays and start debugging the rest of the game.


David Gersic info@zaccaria-pinball.com

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Last updated 7 April 2007