At my place of work I have an Agilent Infiniium 54853A DSO which does not power on after pressing the front panel soft power button. The oscilloscope has been sitting unused for quite a while, for possibly more than a year, but I don't know when it was last confirmed working.
It was actually sent to Agilent/Keysight for RMA, and after paying the $300 repair assessment fee, Agilent said that it needed a replacement power supply as well as a calibration afterwards. The repair and calibration cost was quite exorbitant (roughly $5300 CAD), so it was decided that we would just ship the scope back to us without having Agilent perform the repair.
Here's where things get interesting. I decided to open up the scope myself and have a look at it. I tried searching for a service manual for it, but I could only find a somewhat helpful
troubleshooting guide, and
one other service guide that appears to be same guide, only published more recently. I removed the power supply (after removing the whole PC motherboard first!) and checked the output voltages. Luckily there was a label on the power supply which showed the pinout for the various power headers, plus the aux header which had remote inhibit pins plus 5V standby power on it.
With nothing else connected to the power supply except AC input, the fan on the power supply spins up at a slow speed when AC power is applied. I checked the output DC voltages on the power headers at this point, and got no voltage outputs at all. I took a guess and shorted the "INH-" pin to the aux return pin and the "INH+" pin to the +5V aux pin, then applied AC power once more. This time the fan did not even spin up, which I assumed meant that I successfully inhibited it from powering on! After I pulled out the jumper I added between the INH+ and +5V aux pin the power supply's fan spun up, but this time at a much higher speed. Now when I checked the output DC voltages on the power headers, all were present and correct as described by the pinout label. Now I'm starting to think that the power supply is perfectly fine and not the issue at all!
After some more tinkering I discovered that I can power up the whole oscilloscope if I manually turn on the power supply by first inhibiting it and then un-inhibiting to initiate power on. The front panel soft power button still does not power on the oscilloscope.
However, I found out that if I manually turn the oscilloscope on, then power it off normally and reconnect the internal power supply aux header cable while leaving AC power connected, the front panel soft power button now works! So it would appear that as long as the oscilloscope has standby power, the soft power button works as it should, but once you unplug AC power, you must manually power on the scope otherwise the soft power button does nothing. I can hear a quiet mechanical hum as if the soft power button is trying to power on the oscilloscope, but can't.
Here is a
thread on the Agilent test equipment Yahoo newsgroup that pretty much describes the exact same thing that I was seeing, but I have not yet tried leaving the oscilloscope plugged into AC power for an extended time to see if that allows it to power on.
My next course of action would be to check the wiring leading to the soft power button, to see if something is not making a good connection. Does anyone out there have some experience with these older Agilent Infiniium oscilloscopes and how the soft power on works? The service guide PDFs I found online do not go into detail about how this works.