Maintenance 6
TROUBLESHOOTING
1.Power supplies: +5V dc at U202-1; 0V dc U202-11.
2.μC clock output: 8 MHz at U202-2,-3.
3.Trigger line U202-40 (TP201): Square wave, 50% duty, low 0V, high 3.8V (nominal). The period of the trigger signal should be 12.500 ms for 60 Hz line.
4.Interrupt from A/D (U202-39): Normally low, duration 48 μs occurs approximately 5450 μs after falling edge of trigger signal on TP201 (U202-40).
5.Guard-crossing test pattern (U202-4): Waveform C (see Figure 6-10).
6.Interrupts from watchdog timer (U202-6): Pulsed low for 0.2 sec every 1.5 sec, exponential rise between pulses.
7.Output test patterns (see Waveforms A and B in Figure 6-10): 1 kHz square wave on indicated pins, 50% duty cycle, low 0V, high 3.8V nominal. (The waveforms are interrupted every 1.5 sec for 0.2 sec due to interrupts from the watchdog timer.) To observe these patterns, remove U220, attach a logic clip to address latch U219 and sync on U219-3 for Reference Waveform A on channel 1 of a dual trace scope. Compare channel 1 with waveforms at U202-10,-14,-16,-18,-20,-22,-24,-26,-28. These should all be the same as reference Waveform A (including phase). Then compare channel 1 with waveforms at U202-13,-15,-17,-19,-21,-23,-25,-27,-29,- 33.These should be the same as Waveform B, which is simply the opposite phase of Waveform A.
6-43. | Address Latch (U219) |
| Verify that U219-2, -6, -7, -12, -13, -16, -17 are the same as Waveform A (see Figure 6- |
| 10) on U219-3. Verify that U219-4, -5, -8, -9, -14, -15, -18, -19 are the same as |
| Waveform B. The waveforms should be interrupted every 1.5 sec for 0.2 sec due to |
| interrupts from the watchdog timer. |
| f6-10.wmf |
Figure 6-10. Waveforms for In-Guard Troubleshooting Mode
6-44. External Program Memory (XU222)
Sync on U219-3. Verify that XU222-3, -5, -9, -12, -15, -17, -19, -23, -24 are the same as Waveform A (see Figure 6-10) on U219-3. Verify that XU222-4, -6, -8, -10, -11, -13, -
