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

 

Probably teaching grandmother to suck eggs but:
Have you set the trigger source and coupling appropriately?

 

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.

 

Also, AC/TV switch to AC, and +/- switch makes no difference.

 

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.

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.

 

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.

I have fixed plenty of these in the past, but too long ago to remember anything useful.

Thank you anyway!

 

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.

 

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.

Thanks so much! After replacing the caps and then messing around with the Sweep Stabilty trimmer she started triggering properly!