Zektor Troubleshooting Procedures

ZEKTOR is a "state-of-the-art" electronic microprocessor based, video game. The result of hundreds of hours of work, design, research, experiment and more work. However, as with any electronic device, component failure or other problems can result in a game that doesn't function properly, or doesn't function at all. In either case, your game is "down", and so critically, are your profits.

Your objective is to fix it as quickly as possible, and logical troubleshooting goes a long way toward that repair. Although many troubleshooting methods may be familiar to you, procedural logic is common among them, and might be stated in this order: visual inspection, symptom recognition, symptom isolation, function isolation, component isolation and repair. Familiarity with the equipment in question will allow you to bypass one or more of these steps, as any particular problem may be obvious to you, or may have happened before. In general though, these 6 steps form a good premise upon which to approach your "down" game.

An extremely important item in our procedure is the first mentioned, giving the gear the "once over". A large percentage of failures found in electronics, show themselves visually and often a great deal of time can be saved by inspecting for burnt or blown components, loose or disconnected wiring or connectors, or PCB traces burnt or pulled up. Thorough visual inspections become increasingly important the closer you get to the faulty item, and should be repeated each time another portion of the game is eliminated. Symptom recognition (as with all electronic troubleshooting) in your game depends first, on knowing what a proper display is, and second, knowing how your display differs from a normal one. Symptom isolation follows naturally; (i.e., "I have no picture", "I have no sound", "I have no control over the car", "the picture is scrambled"), ergo, a video, audio, input or logic problem. Function isolation, such as a sync problem with the video, requires that you consider those functions that go to make up video sync. Is it a monitor problem, or an "on-the-board" problem? A monitor input check to verify the signal will tell you. Does the board have the voltage (from the power supply) that it needs? Yes? We must have a board failure, as we've just isolated down to function.

Taking our sync problem further, before we begin our searchfor an individual component, let's reapply that first item in our "Logical Troubleshooting Procedure". Look at the board. Open resistors, diodes, and capacitors often give themselves away.

Noticing a trace literally burned open can save you serious "down-time". The board looks OK, so on we go. Specific component isolation relates to the specific nature of the failure, component commonality, proper inputting (Doth signal and power) and proper outputting (as in the case of an output held high, low, or floating by input port failure in the succeeding state). More general problems (such as a total loss of video sync) requires the more involved procedure of systematic elimination of possibilities. This operation can be expedited however, by dividing the circuit in half, establishing a "go-no/go" at that point, and again dividing the suspect circuit portion in half. The largest possible areas can be eliminated in this manner, dividing and subdividing until the individual component failure is found.

As we've outlined previously, any electronic repair procedure consists of a series of efforts to isolate a problem down to a "managable" level; restating our Logical Troubleshooting Procedure in 6 steps, 1. Visual Inspection, 2. Symptom Recognition, 3. Symptom Isolation, 4. Function Isolation, 5. Component Isolation, and 6. Repair.

In our ZEKTOR game system, we are dealing with, essentially, 3 major functional components:

1. The Power Supply

2. The G-80 Boards (Card Cage Module)

3. The Color X-Y Monitor

So, in a typical maintenance procedure, having isolated down to Function (Step 4.), we would next attempt to determine which of the 3 major elements is defective. In the following paragraphs, we will look at each element and some of its sub-divisions as a guide in isolating further.

Usually, the power supply can be eliminated as the source of a problem if the games comes up on the screen. The major exception is when the game plays normally but no sounds are produced. In this case, the power supply's amplifier circuit should be checked for audio signals from the sound and speech boards. If they are present on the amplifier output, then a bad speaker or connection is probably the cause of the problem. If the signals are not there, susDect the amplifier circuits on the sound and/or speech boards.

If the picture does not appear on the screen, check the power supply fur the main AC voltage to the primary of its transformer; then ensure that the G-80 boards are supplied with the correct DC voltages from the power supply. Also make sure the 3 VAC reset signal is being applied to the CPU board. If all these tests prove normal, then eliminate the power supply as cause of the problem and proceed to check the remaining functional game components - G-80 boards and monitor.

In most cases, a simple test will help to isolate a problem of no picture to either the G-80 boards or monitor. On an oscilloscope, look for varying voltage signals on pins 1 and 4 of the 4-pin Mo lex connector on the Timing Board. If the signals look similar to those shown in Figure 1, check for signals swinging between 0 and +4 volts on the RGB outputs (4-pin Molex connector pins 4, 1, 2 respectively) on the Control Board. If all three outputs are at 0 volts, suspect the X-Y boards. If the signals appear normal, suspect the monitor as the cause of the problem. If however, pin 1 (to the monitors horizontal input) is held at or near +4 or -4 volts DC, suspect one or both X-Y boards. If pin 4 (to the vertical input) is held at or near +3 or -3 volts, suspect the other G-80 ooards. In either case, TURN OFF THE POWER AND IMMEDIATELY DISCONNECT THE X-Y MONITOR. Proceed to check the inputs to D/A converters U1 and U4 (T5) for active signals. Verify that none of the Character Data lines (CD0-CD7) are pulled high or low, or are floating. Check for the XCL and YCL clock signals from U28 (T6). Verify that the 15 MHz crystal clock is operating and that a 40 Hz signal is present on pin-11 of U13 (T7). Check BOS signal to be sure it is not held; signal DRAW should be switching high and low. On the Control Board, observe the signal FETCH to ensure it pulses high and low. Also, none of the Data lines (D0-D7) should be held high, low, or floating (C5). Check for clock signals PCC and SCL (C5).

Look for input changes on U1 and U5 of the color circuit (C6); also, pin-3 of U4 should be active high and low. (See figure 1 in the illustrations section).

When the monitor is suspected of a problem, check for all correct power supply voltages as shown in the schematic. Isolate incorrect voltages to either the monitor power supply or to the circuit receiving the voltage.

NOTE: The Color X-Y Monitor contains a circuit that shuts off the high-voltage oscillator when no vertical or horizontal inputs are present. DO NOT ATTEMPT TO RAISE OR LOWER EITHER INPUT WHEN TESTING THE MONITOR. DOING SO WOULD. CREATE EXCESSIVE DEFLECTION CURRENT THAT COULD SEVERELY DAMAGE THE MONITOR. For testing the monitor, use only the outputs of the G-80 hardware. In addition, DO NOT operate the monitor WITHOUT proper fuses in the main AC line. If a monitor is blowing main fuses, check the deflection amp power transistors Q605, Q606, Q705 and Q706, WITH THE POWER OFF. Shorted transistors or diodes in the deflection amplifiers will also blow main line AC fuses.

Check the transistors in the color drive circuits for shorts or opens when one or more colors is missing from the display, and the G-80 boards are known to be good.

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