Author Topic: TDS3000B trace "ripple"  (Read 281 times)

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Offline perdrix

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TDS3000B trace "ripple"
« on: March 03, 2021, 04:21:50 pm »
Using a TDS3014B (up-hacked to TDS3064B FWIW), feeding it the calibrator signal.

The trace moves up and down by a small amount at about 2Hz.   5V portion of square wave seems to be worse than the 0V portion?

Has anyone seen this and/or have recommendations?

Thanks
David
 

Offline sicco

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Re: TDS3000B trace "ripple"
« Reply #1 on: March 04, 2021, 08:14:33 pm »
The 1 kHz test clip signal comes from a front panel board with its own NEC microcontroller. Start checking the 5V power supply to that board first. I suspect you will see the same ripple. Check with another scope first so that you know for sure what’s root cause: the signal on tge test clip bad, or the scope ADC etc bad.

If that’s not it then check the 2.5 V reference ic on the main board. It’s an 8 pin SOIC, on the middle of the board, near the corner of the metal covered part. Is it ripple free? Unlikely, but you never know. There’s another SOIC-8 closer to the very large IC  MM9595. That’s just a dual opamp. Check for ripple on its outputs.

The 2 Hz you see might be aliasing. The 1 kHz comes from a front panel crystal but the scope itself has its own crystal, 75.7575 MHz. See if the 2 Hz goes up or down a bit if you heat up either crystal.
 

Offline perdrix

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Re: TDS3000B trace "ripple"
« Reply #2 on: March 05, 2021, 01:12:31 am »
Thanks, that makes sense to me ...

However a simple check of the 15V supply suggests I can see myself replacing quite a few electrolytic caps in the near future :(

Ho hum
 


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