Agilent DSO5014 "LED-loop" recovery - worked on two scopes so far!

[Madmanguruman]

Hi all:

Long time lurker and first-time poster. I manage a large lab where we have many Agilent DSO5000-series scopes still deployed. At least 4-5 of them exhibited the "LED-loop" fault where the scope never gets out of the power-on test sequence and keeps cycling the LEDs in the 1-2-3-4 pattern as described in the service manual. Sadly we scrapped a few of these as Keysight/Agilent is charging replacement cost for repair these days (i.e. we just buy new DSOX scopes). In all cases, these failures just randomly happened on a power-up - no external stress / bad measurements, etc. so we were puzzled as to why they would fail.

While doing some probing before scrapping out my last two bad scopes, I managed to resurrect one which has been stuck in the LED-loop for six years! The second scope was also resurrected , this one was stuck for the past 18 months. As usual, do this at your own risk - you broke it, you bought it, etc. - also note that you need the scope open and powered for this, so be careful around the mains.



View shown is the bottom of the 5014 main board with the back cover and EMI shielding removed.

With the scope turned on and LED-looping showing on the front panel (1-2-3-4-1-2-3-4-1-2-3-4 etc) I was measuring the potential of these pins with respect to chassis ground with my DMM, trying to see if any of these might be a serial link or whatever. On the top row, the third pin from the left is at 3.3V potential and the 4th pin is at 0V. I accidentally shorted the third and fourth pins with my DMM probe. The scope immediately reset, did it's usual 1-2-3-4 LED sequence - then step 5 (!) - the Agilent logo came up and it booted! There was no error message or warning on the screen, just the usual information screen (no hardware or firmware concerns). Even the calendar was correct (six years since the last boot-up).

I inserted my USB drive and updated the firmware to 6.20 (it was at 6.15) and so far the unit has persisted - several power off-power on cycles, and a self-cal,  it has booted up each and every time.

Just for fun, I cracked open a second scope with the same symptom. I shorted the same pins together - same thing happened! The scope reset itself, did 1-2-3-4-5-Agilent logo, and it booted! It also seems to keep booting after several power cycles. This scope was already at 6.20 but I reflashed it just in case.

I really don't know *what* this reset does, but it worked for me! There must be a weird bug not related to an actual hardware failure that gets the scopes in this mode, which this glitch/reset trick seems to fix/bypass somehow.

[Madmanguruman]

FWIW, there is a comment in User Cal Status: PANTHERT0A. Guessing this is somehow related to the bootloop.