SDS804X HD - random power-off, latching

[LeCodyMan]

Hello, I am a student in the UK and this is my first
oscilloscope. It is a few weeks old, calibration certificate
dated 7 July 2026. I have searched the SDS800X HD threads
here and found nothing matching, so any thoughts would be
appreciated.

Version: 1.1.6.5 / Uboot-OS 4.8.12 / FPGA 2024-11-26 / HW 00

Problem: The instrument powers off completely and
unpredictably during normal operation.

Test signal: Null - it happens with nothing connected.

Scope settings: Occurs from Default settings, idle on the
default screen, and during normal use. Independent of which
channels are enabled, and of decode, FFT or any other
function.

Observed behaviour:

- Run times so far: 10 min, 5 min, 1.5 min, 93 min, 5 min,
  15 min, and once nearly 2 hours. No correlation with how
  long it has been switched off beforehand, so it does not
  look thermal.

- Audible relay click at the moment of shutdown.

- The standby LED that glows faintly when the scope is off
  also goes out, so the whole supply drops rather than just
  the rails feeding the main board.

- It will not restart while still connected to mains. It
  only recovers after the power cord has been unplugged for
  roughly three minutes, which suggests a latching protection
  circuit clearing once the capacitors discharge.

- Ambient around 22 C, more than 15 cm clearance both sides
  as the manual requires, fan running normally right up to
  the moment it dies.

- *TST? passes and SYST:ERR? returns 0,"No error", so the
  firmware appears completely unaware of it.

I have not opened the case. Does this look like the power
supply module, or could it be something downstream on the
acquisition board? And has anyone seen this on an
SDS800X HD?

Thanks for any help.

[Martin72]

Hi,

It could be a loose connection at the power input, or the plug might not be inserted far enough.
You can feel some resistance when plugging it in, but it's still not inserted far enough.
If you can rule that out, I'd gently tap the scope's casing in various places; if that causes it to shut down, there's definitely a loose connection(somewhere inside-->Warranty).

[LeCodyMan]

Thanks. I have checked the mains lead - it is fully seated
and I have tried a different cable, so I can rule that out.

Tapping the case does nothing either. It is running as I
write this and taps in various places have no effect on it.
There was one occasion where it ran 93 minutes after a light
tap before power-on, but I have not been able to repeat
that, and it has since shut down while booting with nothing
touching it, and once while sitting completely undisturbed.

So it does not appear to be mechanically triggered in any
consistent way.

[Martin72]

Hi,

Then:

It is a few weeks old

Return to retailer...
If you can rule out external mechanical factors, then something is wrong on the inside—I wouldn't want to open it up to check as long as the device is still under warranty.
I know, sending stuff in and all that is a pain; I hate it too... But apparently that's just how it has to be.

[LeCodyMan]

Thanks, that confirms what I suspected. I have already
opened a return request with the retailer.

I was hoping to avoid it as the shipping took a while and I
need the scope, so I was rather hoping it might be something
I could resolve. But you are right that it is not worth
opening while it is under warranty.

[themadhippy]

what about the other end of things,the socket its pluged into,the plug etc

[LeCodyMan]

Good thought - I have tried it plugged directly into a separate wall socket as well as the power strip i normally use, and swapped the IEC lead for a different one.
No change either way.

[tautech]

    
Having supplied many since release....never had a problem with any of them.

Warranty claim is the only sensible path forward.
Keep us posted about the fault if shared from your supplier.

[LeCodyMan]

Thanks, that is reassuring in a way - good to know it is not
a common problem.

Two quick questions if you don't mind. When a fault like
this does come back to you, is it usually handled as a board
or module swap, or does the whole unit get replaced? And is
there anything user-accessible that would give any useful
diagnostic information? *TST? passes and SYST:ERR? returns
no error, so as far as I can tell the firmware has no idea
anything is wrong.

I will post an update once I hear back from the supplier.

[CJSouthern]

I really can't add anything to the above other than, as an owner of that series of scope, to offer a bit of moral support.

I had an iPhone 3GS that had a faulty digitiser out-of-the-box many years ago; it's annoying, but "shite happens" occasionally.

My approach is to "rip the bandaid off quickly"; get a faulty item on it's way back ASAP - hassle them about it if they don't "pull finger" - and usually it's all sorted in a few days (and then forgotten about); especially for an out-of-box failure like that.

[tautech]

Thanks, that is reassuring in a way - good to know it is not
a common problem.

Two quick questions if you don't mind. When a fault like
this does come back to you, is it usually handled as a board
or module swap, or does the whole unit get replaced? And is
there anything user-accessible that would give any useful
diagnostic information? *TST? passes and SYST:ERR? returns
no error, so as far as I can tell the firmware has no idea
anything is wrong.

I will post an update once I hear back from the supplier.

As with any fault diagnosis, the PSU is the first port of call to check it is producing the correct voltages.
Then if all is well mainboard checks are the next step.

We keep a PSU in stock as the same is used in several models but mainboard replacement is a whole different story as they must be configured by Siglent with a SN# to match the unit being repaired.

We are guided by the Service manual:
https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2024/09/SDS800X-HD_ServiceManual_EN01A.pdf