Strange problem on tds3054b

[pasta2018]

Recently i have got a tds3054b,it can pass selftest and spc.However, for each channel when vertical range is 1v/div or up,there is clutter ,each channel is the same. when the range is 500mV or below, it is ok. I checked the ±5V and ±15V is stable and correct.

[pasta2018]

I take some photo

[inse]

Is the phenomenon also visible with 50Ohm termination enabled at the inputs?

[pasta2018]

yes，and AC/DC model also the same

[pasta2018]

sometimes，it can not pass spc. but selftest is always ok

[inse]

Do you have a second scope to verify the supplies are also noise free?

[sicco]

Can you show screenshots with the time base in the nano seconds / div range?

Does the scope level-trigger on these spikes? (trigger mode normal, level at halfway the highest spike level)

Looks like an issue on the digital data bus in between the 4 ADC chips and the largest (MM9595?) chip. Corrosion / moisture / conductive dust bad soldered pin?
Try local cooling / freeze spray at that area.

[pasta2018]

yes,the supply is ok

[pasta2018]

yes,this is the triggered signal

[sicco]

That seems to rule out that the problem would relate to the digital bus between 4 ADCs and MM9595.

The 2.5V reference - is that showing any AC unrest?
This reference also feeds a + and - 2.5V power rail that feeds the ADC chips and also the attenuator modules. Do those +/- power supply rails show any unrest relative to GND when looking at those with another scope?

Some hints on what reference and power supply lines i meam in https://www.eevblog.com/forum/repair/broke-my-tds3000b/ post#20.

[sicco]

is this the same problem? https://www.eevblog.com/forum/repair/help-!-strange-issue-with-tek-tds3054b/msg4532654/#msg4532654

https://www.eevblog.com/forum/repair/help-[/url]!-strange-issue-with-tek-tds3054b/msg4532654/#msg4532654

Is it the same unit maybe?

Do you also run same (quite old) firmware? Tried upgrading to version 3.41?

[pasta2018]

A little different, for my scope,the four channel always display a same wave,the clutter appears randomly.

[pasta2018]

I have upgrade to 3.41.  when the clutter appear, I can here there is little low noise inside,but I can not distinct where it from

[pasta2018]

I checked some voltage，
2.562V
3.302V
-3.340V
are these all right?

[sicco]

The “little noise inside” might be a hint that a power supply rail is overloaded?
But could also be a hint that you have bad caps on those rails.
There’s a bunch of TO220 linear voltage regulators, two do +5 and -5 for just the attenuator modules. Check with another scope if there’s ripple on these lines.
The DC average voltages that you quoted say nothing about AC ripple amplitudes.

Another thing to confirm: if you bypass the mains power supply, and inject 15VDC from a 3 amps capable power supply instead, rigth at the output of the mains power supply, is the problem still there?
No battery pack inside?

[pasta2018]

when I  power on, there is no clutter,after 2-3 minutes,the clutter began to appear.

[pasta2018]

maybe something wrong with MM9595