R&S CMU200: Powers on by itself

[Bicurico]

Hi,

One of my R&S CMU200 units started to power on by itself when in stand-by mode.

Also, upon each reboot it was showing that CMOS had been RESET and to press F1 to continue (that is the soft menu key to the right of the power switch).

I just replaced the CR2032 battery from the CPU module and for sure the CMOS message has been fixed - as expected it was just a drained up backup battery.

Unfortunately the unit still powers on by itself when in stand-by mode.

I guess some capacitor is asking to be replaced but before I waste a lot of time looking into what is causing the issue, I thought I might better ask first if someone has come across this problem before and how it was fixed. The keys on the CMU200 all work fine, so I don't kess it is the keyboard matrix mat.

Regards,
Vitor

[RoGeorge]

Try disabling wake up on LAN from BIOS.

[Bicurico]

Even if it is not connected to any LAN?

The problem is that I don't have any PS/2 keyboard at hand.

But indeed could make sense that the RESET of the BIOS caused this to be active.

Regards,
Vitor

[RoGeorge]

Without a LAN cable (and no WiFi, of course) it shouldn't be possible.  Wake on LAN wakes up the computer only when a magic packet is received.  No LAN cable, no packets.

There is yet another wake up mechanism in BIOS, RTC (real time clock) wake up, if that is set, then the computer will wake up at the set hour.

Other than that, it could simply be power line glitches big enough to induce current in the wires of the power button, and the glitch is interpreted by the motherboard as a power button press.  Could happen if some neighbor has very noisy motors, like power tools switching on/off, maybe a refrigerator or a washing machine motor.  Less common, but it can happen.

[Bicurico]

I found a PS/2 keyboard (from my SGI Indy and O2) ans recalled CMU200 settings AND switched off both available auto switch on options (LAN and Power Loss).

The problem still happens. It is NOT a problem with spikes in my power lines, as I have a 2x CMU200 and 2x CRTU connected to the same outlet and the other 3 units do not switch on by themselfes.

This is either a PSU problem (bad caps) or the soft power button has a fault.

I think it is a PSU problem, because the unit behaves normal when switched on (on the back) for about 5 minutes. Only after this amount of time will it start switching on by itself from soft power off.

This is not a major issue, as I can always use the less convinient power switch on the back. Yet, I do like to keep my equipment in fully working condition...

Regards,
Vitor

[richnormand]

In addition to previously mentioned ideas.

1)
Can you get at the "power good line" and the "psu on command line (ground)" and solder two wires to the outside  to be able to monitor them? There is a pinout of the PSU connector in this thread:
https://www.eevblog.com/forum/repair/rohde-schwartz-universal-radio-communication-tester-cmu200-psu-issues/msg986634/#msg986634

2)
If you have more than one CMU200 a PSU swap would be interesting to sort out if it is the PSU by itself or it is being ordered to turn on by the front panel.
Since these PSUs can work well alone simply removing it and monitoring its output would tell you if it is the PSU that is turning on just by itself.

3)
At the front panel could you have some water in the membrane or something shorting the "on" button or around it?
Is there an "auto-on" function in the BIOS?

Best of luck with it.

[Bicurico]

Thanks richnormand.

I do own several units and I have one half working CRTU spare (broken RF Frontend and lacking at least one board - it does show a spectrum, though). I have the PSU swap on my TODO list, but I could not find time and will-power to do it.

The CMU200/CRTU has lots of screws to remove to get to any of the parts (took me almost one hour to swap the CMOS battery) and I need to really be in the mood to do it. This comes with having to move other stuff on my desk just do be able to take off this CMU200 unit.

I will update this thread as soon as I have some new info.

The purpose of me asking was to know if this is a known issue with a simple fix.

And yes, the BIOS does have two settings which could result in automatic switch-on, but I have both deactivated.

I don't think that the soft power button has a fault, as it takes like 5 minutes for the problem to happen when switching on the back power switch on a cold state.

I guess some capacitor is not OK. Not sure if that would be on the CPU module, some keyboard component or the PSU.

Regards,
Vitor

[richnormand]

I know what you mean!

When I took out my CMU200 PSU that is when got this baby from eBay. Pretty cheap at the end.
Saved my bacon (Cdn expression?) when I had to remove (several times) the cover of the RxTx module too.

I find it most useful in day to day operation.

[pa4mic]

Hi,

Just wondering if you have found the problem as my unit have it two now.

Thx in advance

Mike

[Bicurico]

Hi,

Unfortunately I have not fixed it.

Because my electricity bill was getting out of hand, I started to disconnect all my equipment from power, when not in use. And in the process I discovered how little I use most of the gear. As such, I forgot about this issue.

Back on topic: I am pretty sure the issue is with some capacitor in the PSU that needs replacement and causes this soft switch on.

Let me know if you find a solution.

Regards,
Vitor