Telequipment D61a Triggering Issue

Discussion in 'Technical Repair' started by m2circuits, Jul 17, 2016.

  1. m2circuits

    Thread Starter Member

    Jul 17, 2016
    52
    1
    I recently acquired a D61a, and on first power up I connected ch1, then ch2 to the CAL signal. Both channels do not seem to be triggering properly - adjusting the Trig Level just slows down the display and the Auto Trig doesn't make much of a difference. I have not replaced the filter caps yet, as I am waiting for them to arrive. In the mean time I checked the notorious R95(others have said that this resistor drifts high), but it checked out within tolerance. Has anybody run into this issue? Could it just be the caps? Or is there another problem that is common with these scopes?

    Thanks,
    M
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    Probably teaching grandmother to suck eggs but:
    Have you set the trigger source and coupling appropriately?
     
  3. m2circuits

    Thread Starter Member

    Jul 17, 2016
    52
    1
    Yup, DC coupled and Trig set to ch1 or ch2 respectively. I've also tried a sine wave from an audio gen. and I can get it trigger occasionally - but more often then not it just scrolls slowly past the screen, and no matter where I position the Trig knob(or Auto) it just won't trigger.
     
  4. m2circuits

    Thread Starter Member

    Jul 17, 2016
    52
    1
    Also, AC/TV switch to AC, and +/- switch makes no difference.
     
  5. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    Yeah, thought so, but I thought it was worth mentioning.
    I have fixed plenty of these in the past, but too long ago to remember anything useful.
     
  6. m2circuits

    Thread Starter Member

    Jul 17, 2016
    52
    1
    I'm hoping it's just the supply caps. I've checked various voltages and some appeared a bit low:

    7.5v is @ 7.2v (can be adjusted via trim pot)
    13v is @ 12.2v

    I feel like it may be the caps dragging it down a bit, but won't know for sure till the caps come.

    Thank you anyway!
     
  7. RichardO

    Well-Known Member

    May 4, 2013
    1,235
    384
    I seem to remember that the trigger circuit is a bit odd. In auto mode, it is an oscillator that free runs unless there is a trigger signal. Look at the calibration procedure for the triggering. Maybe trying to calibrate it will point you to the problem.
     
  8. m2circuits

    Thread Starter Member

    Jul 17, 2016
    52
    1
    Thanks so much! After replacing the caps and then messing around with the Sweep Stabilty trimmer she started triggering properly!
     
    RichardO likes this.
Loading...