Keysight MSOS104A Repair Attempt

[BeamDump]

Good find.
Still going?

[seebeck]

Hi Extrasolar,

The same PLL2 issue happened to my Keysight DSO-S 404A Digital Storage Oscilloscope.
You mentioned a replace of all the Power Rail Caps（tantalum mostly） around the time-base area, was it just that?
Thanks a lot.
I will try to repair my DSO this weekend.

With best regards.
Seebeck.

[veloyage]

Hi all,
TLDR: I just made an account to tell you that Keysight seems to repair this issue for free
We have a DSOS054A which has been sitting unusable with this error for a year or so. I looked around and found only this thread, with repair seeming very difficult, so it sat some more. With the note about a recap being successful I recently opened it up, checked it out, and put some tantal caps into my mouser cart. Before actually doing it though I wanted to hear from Keysight what an official repair would cost, and while going to create a service request I found some service notes which detail the repair procedure (board swap), the most recent one (https://keysightsales.file.force.com/sfc/dist/version/download/?oid=00D1a000000awb5&ids=0685a00000nYQsW&d=%2Fa%2F5a000002gh2L%2FmeC7tIclK9L9B1_CDON938jLsjuTkG8X0XQbeUeKEKg&asPdf=true) saying "NO CHARGE AVAILABLE UNTIL: December 31, 2023".
So I wrote them and got told to send it to DHL for forwarding and subsequent repair "on warranty". The actual warranty ended years ago, but for this known production issue they seem to not care about that.
I am not sure if the "no charge" will actually expire or they will extend it again, as they seem to have done before.

Hope this helps someone,
Thomas

[HighVoltage]

 "NO CHARGE AVAILABLE UNTIL: December 31, 2023".

Hope this helps someone,
Thomas

What a nice surprise, good to know.
Keysight sometimes is very generous with scope problems, even if they are out of warranty.

[BeamDump]

Haven't  tried to continue  repairing mine yet. So much work,  it's nearly impossible to find free time for  anything else anymore.

Last time i brought this problem up with Keysight they quoted me an initial 6000EUR cost for replacing acquisition board. I've sent them  another request referencing the attached service note.  Let's see what happens.

[BeamDump]

Well i can safely say that replacing all tantalum caps on board, doesn't solve the PLL2 problem. Still same effect, lock light on but soft start with fault and nothing past that.

Thanks to Extrasolar but not the solution. 

[Extrasolar]

Hello All, It has been a while !!

I restarted my repair on the MSOS104A. Recaping does not solve the issue. It is a serious problem that perhaps has a lot more to do with Firmware !!
I was told that a recent Firmware update, effectively solved this issue on a known PLL2 Timebase failure unit.
I am going to try to reinstall windows and the scope drivers from the most recent firmware update from Keysight.
For some strange reasons, the SSD on the scope broke all of a sudden and there are only 2 options to save it now : 1: install from scratch and hope for the best, 2:send to Keysight and pay ...
I will update the progress soon ...

Kind Regards

[Extrasolar]

Hi All,

I successfully installed the instrument drivers on a freshly installed Win 10 system. The acquisition board is recognized properly and the software works fine. However the PLL2 problem persists...

I have managed to prove that the scope actually works when we operate it remotely via USB:
There are different waveforms I wanted to test and curiously enough the scope followed with the :DIGITIZE command.

This makes me think the problem is actually some sort of firmware/software bug.

Kind Regards

[BeamDump]

I got to talking with Keysight. PLL2 light will come on even if there is problem with VCO and the entire issue here is the VCO.

What they told me: " The VCO and perhaps the synthesizer that drives it. But right now VCO is the concern as it swings widely in the MHz on the output. Even though board shows it's in a lock, it's obviously false.

[hch]

Hello,
first I'd like to thank all contributors to this thread, which turned to be paramount to fix problem with our MSOS104a. Our problem had very similar symptoms to these mentioned here.
We narrowed search for fault by cooling (using freezing spray) area of time base and found that if we cool down the VCO chip we were able to obtain PLL2 lock.
Finally we replaced the part with stock CVCO55BH-4940-4940 (Thank you again for info that VCO is 5GHz which turned to be correct )
After replacing the VCO the warning "Timebase error detected in PLL2" finally disappeared and scope seems to be working, at least for now

[HighVoltage]

That is a nice confirmation with CVCO55BH-4940-4940, thanks!

[Calzie]

Hi there, I also can confirm this part CVCO55BH-4940-4940 (from Mouser $30 plus post) fixed the PLL2 error with my MSOS804A scope.
Bit tricky getting the old part off, there are lots of small surface mount components really close by, I put several layers of Kapton tape over them and used hot air at 440C, took a while as the devices shield can is a big head sink. The device is only secured by the 10 joints, three are signals and easy, the rest are to a large PCA ground plane (and the devices ground and case) these take a while to melt, there is no central solder ground under the device.
Its also tricky fitting the new device as the clamps for the circuits covering shield can limits solder iron access not helped that the large ground needs a big iron to solder.

Ran the scope for 1 hour without issues, passed its self tests ok, magic result, thank you.

Calzie
Edinburgh, UK