Agilent 33120A function generator -- Error 771 - Page 1
Forum section: electronics / repair

author: Signal32
author_rank: Frequent Contributor
timestamp: July 27, 2016, 06:04:39 am
content: Hello,Today my Agilent 33120A suddenly started booting with the "Err" indicator lit up. It happened after i powered it off, waited ~10 seconds then powered it on again.Looking at the error codes, it shows only error 771.Here is what Agilent says on their website about this error:QuoteSelf-test passes, the error happens at power on. The function generator still works, but presumably without using any calibration constants.I looked inside and there doesn't seem to be any battery-backed nonvolatile memory in there. So I'm guessing the failure is inside a flash chip.Has anyone had any experience with this type of issue ? Does anyone have any suggestions ? I'm thinking that even if I send it in for calibration the error won't go away since it happened so randomly.Thanks!

author: caiser01
author_rank: Regular Contributor
timestamp: October 13, 2021, 09:46:01 pm
content: Apologies for resurrecting an old thread but I experienced the same issue with an HP 33120A today and was able to resolve it painlessly.I just purchased one of these units on ebay and it arrived today. On first power up, everything worked but the 'Err' indicator was lit. Digging into the menus revealed the single error code 771. Unit passed the self-test with no errors. After finding this thread and digging a bit in the service manual, I was investigating the possibility of calibrating this unit. During that process, I stumbled on to a solution by following this process:1. Under the CAL menu, set the unit to 'UNSECURED' (default passcode is 033120; procedure described on page 47 of the service manual)2. With the unit now in the 'UNSECURED' state, power it off.3. Wait a few seconds and power back on.4. Check the CAL menu and verify the unit is still 'UNSECURED'.5. Set the unit back into the 'SECURED' state (again default passcode 033120)6. Power off, wait a few seconds, power back on. No more Error 771!It's possible your unit may have had the passcode changed to something other than the default. If so you'll have to open the case and short the pads at JM101 as described on page 65 of the service manual in order to bypass the code.Basically, we're unsecuring to perform a calibration but then resecuring without calibrating anything. Not certain why this resolved error 771 but my theory is that the act of securing the device perhaps recalculates the offending "Nonvolatile cal memory checksum" to a valid value.YMMV but just wanted to share this as a possible resolution for anyone else who may have experienced this scenario.Incidentally, I did run through the quick check procedures outlined in the service manual and my HP 33120A appears to be functioning correctly within spec.

author: Yansi
author_rank: Super Contributor
timestamp: October 13, 2021, 10:24:11 pm
content: just a note - if the units store the CAL data within a battery powered SRAM, it as well may be possible, the battery is dead and the SRAM on the edge of loosing its content. Hence why the corrupted data detected by an incorrect chksum. So even though you clear the error, the cal may in fact be corrupted.I would at least check the unit thoroughly, if it is withing the spec, if not trying to recal it, as most likely the cal is long long time due.

author: TheSteve
author_rank: Unknown
timestamp: October 14, 2021, 02:53:02 am
content: There is no battery inside a 33120A. Odds are some value was corrupted in cal memory. Unlocking and relocking etc recalculated the checksum for that data. So something in the cal data was changed and could be off unless it was the actual checksum value itself that had become corrupted. It may still function perfectly or something may be slightly off, or even off a decent amount but finding that could be quite the challenge.