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Strange oscilloscope screen problem...

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Tricka90:
I've bought an used Hameg HM304 oscilloscope. I'm a beginner so that's my first one.
I found that the oscilloscope screen has a strange problem when I use "X-MAG X10" function to zoom the waveform a lot.
In the video below you can see how the wave deforms  in different ways.
The more I increment TIME/DIV value the more the wave deforms. But if X-MAG X10 is not active the wave show perfectly (but it's too little to be measured accurately, of course).
In this video I'm measuring a 12MHz wave from a PIC external crystal oscillator and moving it around horizontally. The probe is set to 10X.
Can I do something to fix this problem?
Do you think is an hardware issue or it can be solved just with some calibration?

Here's the video:

israel:
Hi, You can check the bridge rectifiers and capacitors in the power supply. Sounds like a leaky rectifier, is a typical problem in such HAMEG oscilloscopes.

With the help of a multimeter that has bargraph may see the oscillation of 50 Hz at the output of the rectifiers. Any of them that excessively hot show, is sign of leakage in one of the diodes.

If this does not work you will have to go forward with the help of the service manual and diagrams.

Regards and good luck in the hunt  :-+

dfmischler:
In the first part of the video, it looks to me like the horizontal sweep ramp is not stable (it's running faster then stabilizes to a slower speed).  It looks kind of like my old Tek analog scope on mixed sweep with the knobs unlocked, but the fast part is before the slow part.  Where it looks kind of "ghostly" later in the video looks like a triggering problem (i.e. that part of the waveform is not repetitive enough to look solid).  Without more information, there is no way for us to tell if the input waveform is unstable there, or if the scope is messing it up.

Tricka90:
Thank you a lot for the help. I will follow your instructions, starting with the ones provided by "Israel".
I'm sorry I don't speak english very well. You're saying that I should check the bridge rectifiers output in the power supply for the X-Mag? Or in the general power supply?
I didn't understand what exactly should I measure with the multimeter. You say I should measure the output of the rectifier, so why should I find 50 Hz oscillations if it has been already rectified?
I'm sorry, my multimeter doesn't have bargraph...maybe I can measure it with the oscilloscope itself?

dfmischler, if you need more information I'll happily give them. Please ask me any information you need  :)

israel:
The check would be the electric supply in general. The multimeter with bar graph is useful in the dc current measure, show oscillations of the bar if it contains ac current.

In no event Use the oscilloscope itself to make these checks. Otherwise the god Thor and Smoke invade your room, you can use other additional oscilloscope. Giving always miss the measure to be limited only to the transformer secondary and never to  domestic ac supply , since otherwise there will also be BANG! :-BROKE

I attach the the power supply diagram of  HM-604 model which is quite similar to the 304

Regards,



my English is pretty bad also. although not as much as the Mrs mayor of Madrid :palm: :palm:

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