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Hello everyone!
I have a Tektronik TDS 360 on which the trigger no longer works: The signal does not "stand" at the set trigger time, but "runs" across the screen, although the source and level for the trigger are set correctly. I use the internal calibration signal for the probe compensation (1 kHz @ 5V) as the test signal, but external signals do not work either. Fortunately, the circuit diagram is available at . I tried to check the logic and got stuck here, for example: Page 240 - TRIGGER LOGIC AND TIME INTERPOLATOR A11, A12 for TDS 360 (see also: /g/TekScopes/photo/295258/3786193?p=Created%2C%2C%2C20%2C2%2C0%2C0) MC10121 (U307): Pin 3 is permanently at 3.3V Pin 4 (inverted output of pin 3) is at ~4.4V --> Shouldn't pin 4 be low or at least at a lower potential than pin 3 or do I not understand the logic (ECL? Sorry, i'm not an professional EE engineer) MC10131 (U308A): Pin 5 gets the adjustable holdoff pulse (here set to 1 ms). Two observations: (1): Pin 3 remains permanently at 3.3V, although it should be reset with the holdoff pulse? (2): The holdoff pulse is not stable and reappears sporadically (see pictures /g/TekScopes/photo/295258/3786194?p=Created%2C%2C%2C20%2C2%2C0%2C0 and /g/TekScopes/photo/295258/3786195?p=Created%2C%2C%2C20%2C2%2C0%2C0). The supply voltage of the ICs is stable at 5V. Another thought: The ASIC AOG292 (U401 on page 242) generates the holdoff pulse. There are no data sheets to check some timings, but the mode of operation is essentially described on the previous pages. Before I go any further into the measurement, can you confirm that at least the ICs U307 and U308A are working correctly? At least the behavior of U308A seems strange to me. Thank you very much for your inputs and thoughts! Daniel |
