Agilent MSO-X 3024A one channel crapped out

[Leo Bodnar]

My trusty MSO-X 3024A oscilloscope's channel 3 seems to have cacked out.

The faulty channel sometimes works fine but occasionally drifts off and displays random signal. 
I have been triggering from it when it happened this time and triggering stops as well which points to the analogue frontend.
Sometimes it comes back after some time and power cycle, sometimes - not.

The scope hardware has not been modified apart from PSU replacement a few years back.

Attached picture shows the signal with input disconnected - no probes or BNC cables.
The problem only seems to affect 500mV/ to 5V/ input ranges - the 200mV/ and less are OK.  Owners would know that you can hear relay click going from 200mV/ to 500mV/.

Sounds like a bad input range relay, doesn't it?
Anybody had this?  Anybody fixed theirs?

Cheers
Leo

[TheSteve]

I've never seen anyone with this issue before. Could be a relay, could be an attenuator maybe?
All 4 channels are the same so it should be possible to compare them at the PCB level, not much fun to run the scope when it is in pieces though.

You should update your firmware - if you have anything that is Agilent branded it may be possible to suffer from NAND corruption.

[Leo Bodnar]

Thanks, Steve.
I had to repair input relays before.  1990's LeCroy input RF reed relays often fail.  I have replaced 5 or 6.
Leo

[wraper]

Try slapping it when the issue happens. If it's a bad relay, there is good chance that contact will be restored.

[Hexley]

I had a very similar problem on my DSO-X 3024A, in which the behavior of one channel changed when the attenuator relay changed state. I retouched the solder joints on L1 and R1 (see attached image, which is borrowed from the main hack thread). That restored proper operation. In my case, those components had been changed as part of the bandwidth upgrade mods that I had done earlier, so it was not the fault of the Agilent factory. Sounds like your situation is different, but perhaps a close inspection of that area is in order.
Good luck.