HP 1742A Oscilloscope issue. All the Uncal lights are on

[Easom]

I have an HP 1742A Oscilloscope that worked fine until my kids flipped all the switches and now all the red Uncal lights are on. How do I repair this. I didnt find the answer in teh manual. If it is can someone send me a link to how to fix it or tell me what page its on. That is the only issue it is having right now. Any help would be awesome. CODY

 

[KrisBlueNZ]

Hi Cody and welcome to Electronics Point

I'm not familiar with that model, but in my experience, the Uncal indicators light up when the fine adjustment potentiometers (for the channel gains and the timebase speed) are turned anywhere except their switched position.

These potentiometers have a click switch at one end of their travel, like old fashioned volume controls that incorporated the on/off switch so when you turned them fully anticlockwise they went 'click' and switched the appliance off.

With oscilloscopes the click is probably at the fully clockwise end of rotation. When they are set to that position, the numbers on the vertical sensitivity switches, and the horizontal speed selector, apply directly to the display. When they are set elsewhere, the relevant divisions on the display no longer correspond accurately to the values marked on the rotary switches, and the scope warns you of this by illuminating the relevant Uncal indicator.