Monday, 9 March 2020

Pinball Shadow : Testing the DMD

    Diagnosing Other Problems.
    If you are sure the display itself is working, there are some other things to check when a DMD doesn't work.

    Make sure to check fuses F601 and F602 (all WPC games). F601 is used for +62 volts, and F602 is used for -113, -125 volts. On WPC-S and before, these are 3/8 amp fast-blo 1.25" fuses. On WPC-95, these are T0.315 amp 5x20mm fuses.
It's easier to test voltages at the dot matrix display itself than at the
controller board. Use the "key" pin for reference to figure out which is pin 1
and pin 8.

testing voltages

    Testing DMD Voltages.
    If the fuses are good on the dot matrix controller board (or audio/visual board for WPC-95), you should next check the power at the DMD itself. Voltages used are +62, +12, +5, -113 and -125. Check these voltages at the dot matrix display, or at connector J604 on the controller board. The pin out is:
    • Pin 1: -125 volts
    • Pin 2: -113 volts
    • Pin 3: Key
    • Pin 4: Ground
    • Pin 5: Ground
    • Pin 6: +5 volts
    • Pin 7: +12 volts
    • Pin 8: +62 volts
    If the -125 volts is missing, -113 volts will be missing too. All voltages should be pretty much right at the above specs. If they are not, you need to rebuild the dot matrix controller. 
      Display and fuses good, but still missing or low voltages.
    If you have checked the fuses, and you know the display itself is good (tested in another game), you will need to rebuild the Dot matrix controller board. Usually it's either or both of the MJE power transistors (the ones with big heat sinks) at locations Q1 (WPC-95) or Q3 (WPC-S and prior), and Q6. If you want to rebuild the entire power sections, here are the components to replace.

    • MJE15030: Q1 on WPC-95, Q3 on WPC-S and prior. Controls the +62 volts. Connects to F601 to BR1 (and D3 and Q2, Q10 and R4, R3, R12 on WPC-S and prior).
    • MJE15030: Q7 on all WPC versions. Controls the -113 volts (connects to Q6 and D6 and R8, R9 on WPC-S and prior).
    • MJE15031: Q6 on all WPC versions. Controls the -125 volts (and -113 volts). Connects to F602 to BR2 (and D4, D5 and Q4, Q5 and R5, R6, R13 on WPC-S and prior).
    • MPSD02: Q2, Q10 on WPC-S and prior. Q2, Q3 on WPC-95.
    • MPSD52: Q4, Q5 on WPC-S and prior. Q4, Q5 on WPC-95.
    • 2N3904: Q1 on WPC-S and prior only).
    • 1N4759 (62 volts): D3 on WPC-S and prior. D2 on WPC-95.
    • 1N4758 (56 volts): D4, D5 on WPC-S and prior. D1, D18 on WPC-95. Doesn't fail as often as the other above listed components.
    Also you will need to check resistor values. They should be within 10% of spec:
    • 4.7k ohms, 5 watts: R8 on WPC-S and prior, R43 on WPC-95. Replace if it looks at all damaged, even if it measures OK.
    • 1.8k ohms, 5 watts: R9 on WPC-S and prior, R44 on WPC-95. Replace if it looks at all damaged, even if it measures OK.
    • 120 ohm 1/2 watt resistors at R4, R5 (WPC-S and prior only).
    • 47k ohms 1/2 watt at R3, R6, R12, R13 (WPC-S and prior only).
    Generally either Q1/Q3 or Q6 will go bad. If either of these fail, both should be replaced(make sure you use white heat sink compound when replacing these, and make sure you have them screwed tightly to their heat sinks). The MJE at Q7 comes after Q6, so it usually survives. Also the smaller switching transistors that are connected to Q1/Q3 and Q6 should be replaced (MPSD02 and MPSD52). Finally the zener diodes 1N4759 (62 volts) should also be replaced. The diode 1N4742 (12 volts, D6, D8 on WPC-S and prior and D3, D5 on WPC-95) generally do not go bad. On WPC-S and prior, check the 120 ohm 1/2 watt resistors at R4, R5 and 47k ohms 1/2 watt at R3, R6, R12, R13. Also check the 4.7 ohms 5 watt and 1.8k ohms, 5 watt resistors. Replace any resistors that are out of tolerence or that appear burnt. Always mount the resistors slightly above the board to allow air flow below them. 

    Cloudy Dot Matrix Display.
    This is usually caused by heat related problems. Fixing this could be as simple as adding new white heat sink compound to Q1/Q3, Q6, Q7. Also make sure they are tight to their heat sink. 

    Wavy Hum-bar in the Dot Matrix Display.
    If you WPC-S or earlier dot matrix display has a "wavy hum-bar", try replacing capacitors C6, C9 and C10 on the dot matrix controller board. These are .1 mfd 500 volt caps that filter the DMD high voltages. If they caps fail, you will get the hum bars. 

    Crystallized Solder Joints.
    If a DMD display is not displaying correctly, and the voltages seem Ok, also check this. It's common for the solder joints on the zener diodes in the power section to crystallize, causing heat damage, excessive resistance, and finally a lost of voltage regulation. This can then lead to a failed DMD and damaged power circuits. These diodes are D3, D4, D5, D6 on the dot matrix controller board. 

    Replacing Q2/Q10 and Q4/Q5 on the Dot Matrix Controller board.
    On WPC-S and prior games, the dot matrix controller board uses two MPSD02 and MPSD52 transistors. More common transistors are available for replacement. A 2N5551 can be substituted for the MPSD02, and a 2N5401 can be used for the MPSD42. 
    Testing DMD Controller

    6.25.12 Failed RAM

    Most failures of the DMD controller that are not attributed to the high voltage section are caused by failed 6264 static RAM at U24. 
    Since the RAM is very susceptible to electrostatic discharge, they are often damaged by improper handling. 
    Sometimes, they just fail. Failure of this RAM manifests in many ways, including some shown below. 

    At the very end of "display test" the MPU performs a read/write test of the RAM. 

    If the MPU is able to communicate properly with the DMD controller, 
    riting to and reading from the 6264 at U6, then the message "RAM TEST OK" is shown on the display. 
    Any other message indicates a failure of the test. 

    Test failure may be due to the I/O buffers on either the MPU or the DMD controller, the ribbon cable, or the actual RAM.

    Note: A YouTube video of a successful display test can be found here. 

    6.25.13 Page Errors

    There are 2 pages of 16 memory locations (0 to 15) stored in RAM on the DMD controller board. In the Display diagnostics it will run the page test and display any possible faults on either the low page or the high page (page 1 and 2 respectively) If you are only seeing errors on page 1, look to change out U33, most likely at least one output stuck high (pins 2,7,10,15). Page 2 errors the likely culprit is U35. Both devices are 74LS175. If you are seeing the same errors on both page tests, most likely it will be U16, a 74LS157, which is the A/B selector between the two page addresses.

    Page errors will also throw up a RAM address error. The RAM is not at fault, just how it is addressed by the page selectors. It should clear after attending to the above

    Note: the coin door buttons for advance/go back can be held down to quickly move through display test.

    6.25.14 Failures of Various Logic ICs on the DMD Controller

    The following images represent various failures associated with specific ICs on the DMD Controller board. Of course, the specific way that an IC fails will influence what is displayed. That is, your mileage may vary.

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