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.
controller board. Use the "key" pin for reference to figure out which is pin 1
and pin 8.
- Testing DMD Voltages.
- 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 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:
Display and fuses good, but still missing or low voltages.
- 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.
- 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).
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.
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.