Sometimes knowing what something means is half the battle. Agilent 54831B error. - Page 1
Forum section: electronics / repair

author: Jwalling
author_rank: Unknown
timestamp: August 20, 2016, 03:34:31 pm
content: Sometimes knowing what something means is half the battle. Even better is when you can reproduce in real-time and actually *see* the fault on the screen. In this case, I have been unable to see any impact on the operation of the scope. I've been using it on my bench since 2012 as my main scope with this fault. It seems to be working perfectly! Model is an Agilent 54831B (now a 54832B)That fails the trigger calibration on all four channels.It reports for each channel (where X = channel #):CHAN X trigger errorsPred DelayLooking through the files it creates from a cal routine for ASCII strings.Framecal.dat has references to a "Predator Thresh Delay" and a "Predator Prop Delay"It also creates a file called CalDebug.txt. In it is the following:Code:Starting ---- Pred Delay Chan 1 ----PredII Delay:DacValue 4047, measured value -13.353395 nsDacValue 4044, measured value -13.341964 nsDacValue 4041, measured value -13.351937 nsDacValue 4038, measured value -13.339552 nsDacValue 4035, measured value -13.332947 nsDacValue 4032, measured value -13.353590 nsDacValue 4029, measured value -13.354949 nsDacValue 4026, measured value -13.360570 nsDacValue 4023, measured value -13.336095 nsDacValue 4020, measured value -13.349425 nsDacValue 4015, measured value -13.347497 nsDacValue 4010, measured value -13.336314 nsDacValue 4005, measured value -13.343502 nsDacValue 4000, measured value -13.341724 nsDacValue 3990, measured value -13.343192 nsDacValue 3980, measured value -13.344093 nsDacValue 3970, measured value -13.341962 nsDacValue 3960, measured value -13.345629 nsDacValue 3940, measured value -13.362776 nsDacValue 3920, measured value -13.340799 nsDacValue 3900, measured value -13.350159 nsDacValue 3850, measured value -13.340446 nsDacValue 3800, measured value -13.356761 nsDacValue 3700, measured value -13.336536 nsDacValue 3600, measured value -13.353269 nsDacValue 3500, measured value -13.349758 nsDacValue 3400, measured value -13.326202 nsDacValue 3300, measured value -13.334139 nsDacValue 3200, measured value -13.346145 nsDacValue 3100, measured value -13.345421 nsDacValue 3000, measured value -13.349342 nsDacValue 2500, measured value -13.342110 nsDacValue 2000, measured value -13.349216 nsDacValue 1500, measured value -13.351903 nsDacValue 1000, measured value -13.340774 nsDacValue 500, measured value -13.357989 nsPredator Clock had 36 pointsNot enough points to cover to -5.000000e-009>>Time 6 SecondsFinished ---- Pred Delay Chan 1 ---- FAILEDIt seems to be pointing to a possible DAC failure. Interesting to note that as the DAC count decrements in an orderly fashion, the timing in ns does not. Anybody seen something similar? I do have some parts ACQ boards, my next step is to look at one of them and see just how many DACs on on the board.

author: Jwalling
author_rank: Unknown
timestamp: August 20, 2016, 03:38:03 pm
content: What a dumb ass I am.I have a working unit. I'll get the CalDebug.txt from that and add it to this message.

author: Jwalling
author_rank: Unknown
timestamp: August 20, 2016, 04:12:12 pm
content: Here's the relevant section of the cal log from a working 54831B that is now a 54832BCode:Starting ---- Pred Delay Chan 1 ----PredII Delay:DacValue 4047, measured value -26.506960 nsDacValue 4044, measured value -25.140730 nsDacValue 4041, measured value -23.837760 nsDacValue 4038, measured value -22.617230 nsDacValue 4035, measured value -21.569417 nsDacValue 4032, measured value -20.556526 nsDacValue 4029, measured value -19.718843 nsDacValue 4026, measured value -18.904307 nsDacValue 4023, measured value -18.169278 nsDacValue 4020, measured value -17.461358 nsDacValue 4015, measured value -16.454694 nsDacValue 4010, measured value -15.536123 nsDacValue 4005, measured value -14.709744 nsDacValue 4000, measured value -13.974669 nsDacValue 3990, measured value -12.731329 nsDacValue 3980, measured value -11.677745 nsDacValue 3970, measured value -10.784454 nsDacValue 3960, measured value -10.029580 nsDacValue 3940, measured value -8.852160 nsDacValue 3920, measured value -7.897604 nsDacValue 3900, measured value -7.146338 nsDacValue 3850, measured value -5.791833 nsDacValue 3800, measured value -4.935967 nsDacValue 3700, measured value -3.817691 nsDacValue 3600, measured value -3.138679 nsDacValue 3500, measured value -2.709593 nsDacValue 3400, measured value -2.434677 nsDacValue 3300, measured value -2.234768 nsDacValue 3200, measured value -2.034764 nsDacValue 3100, measured value -1.882188 nsDacValue 3000, measured value -1.753784 nsDacValue 2500, measured value -1.424039 nsDacValue 2000, measured value -1.303628 nsDacValue 1500, measured value -1.279799 nsDacValue 1000, measured value -1.301880 nsDacValue 500, measured value -1.292715 nsPredator Clock had 36 pointsMax curve fit error 97ps at 5nsSection 0 -5.000000e-009 Clk cal 1st Order Term 4.049588e+003Section 0 -5.000000e-009 Clk cal 2nd Order Term -1.018690e-006Section 0 -5.000000e-009 Clk cal Offset Term 8.200001e-010Max curve fit error 23ps at 10nsSection 1 -1.000000e-008 Clk cal 1st Order Term 4.093055e+003Section 1 -1.000000e-008 Clk cal 2nd Order Term -1.249050e-006Section 1 -1.000000e-008 Clk cal Offset Term 6.600001e-010Max curve fit error 23ps at 10nsSection 2 -1.500000e-008 Clk cal 1st Order Term 4.095291e+003Section 2 -1.500000e-008 Clk cal 2nd Order Term -1.261547e-006Section 2 -1.500000e-008 Clk cal Offset Term 7.200001e-010Max curve fit error 62ps at 14nsSection 3 -2.000000e-008 Clk cal 1st Order Term 4.105554e+003Section 3 -2.000000e-008 Clk cal 2nd Order Term -1.631854e-006Section 3 -2.000000e-008 Clk cal Offset Term -1.590000e-009Max Data Dac Setting 4080Data Delay Value for , 26.506960ns, 4042Data Delay Value for , 25.140730ns, 4038Data Delay Value for , 23.837760ns, 4034Data Delay Value for , 22.617229ns, 4033Data Delay Value for , 21.569416ns, 4029Data Delay Value for , 20.556525ns, 4025Data Delay Value for , 19.718843ns, 4022Data Delay Value for , 18.904307ns, 4018Data Delay Value for , 18.169278ns, 4017Data Delay Value for , 17.461359ns, 4013Data Delay Value for , 16.454694ns, 4006Data Delay Value for , 15.536123ns, 4001Data Delay Value for , 14.709744ns, 3997Data Delay Value for , 13.974669ns, 3990Data Delay Value for , 12.731329ns, 3978Data Delay Value for , 11.677745ns, 3969Data Delay Value for , 10.784453ns, 3957Data Delay Value for , 10.029580ns, 3946Data Delay Value for , 8.852161ns, 3922Data Delay Value for , 7.897604ns, 3901Data Delay Value for , 7.146339ns, 3877Data Delay Value for , 5.791833ns, 3818Data Delay Value for , 4.935967ns, 3762Data Delay Value for , 3.817691ns, 3638Data Delay Value for , 3.138679ns, 3498Data Delay Value for , 2.709593ns, 3370Data Delay Value for , 2.434677ns, 3229Data Delay Value for , 2.234768ns, 3066Data Delay Value for , 2.034764ns, 2917Data Delay Value for , 1.882188ns, 2733Data Delay Value for , 1.753784ns, 2457delta Pts 5Max curve fit error 32ps at 2nsSection 0 -5.000000e-009 Clk cal 1st Order Term 4.070445e+003Section 0 -5.000000e-009 Clk cal 2nd Order Term -1.218494e-006Section 0 -5.000000e-009 Clk cal Offset Term 9.800001e-010Max curve fit error 60ps at 8nsSection 1 -1.000000e-008 Clk cal 1st Order Term 4.099052e+003Section 1 -1.000000e-008 Clk cal 2nd Order Term -1.438176e-006Section 1 -1.000000e-008 Clk cal Offset Term 6.600001e-010Max curve fit error 171ps at 14nsSection 2 -1.500000e-008 Clk cal 1st Order Term 4.088170e+003Section 2 -1.500000e-008 Clk cal 2nd Order Term -1.223074e-006Section 2 -1.500000e-008 Clk cal Offset Term 1.460000e-009Max curve fit error 399ps at 18nsSection 3 -2.000000e-008 Clk cal 1st Order Term 4.107018e+003Section 3 -2.000000e-008 Clk cal 2nd Order Term -1.804192e-006Section 3 -2.000000e-008 Clk cal Offset Term -1.580000e-009>>Time 145 SecondsFinished ---- Pred Delay Chan 1 ---- PASSEDThe test ran much further along as everything converged OK. As expected, the DAC value decrementing coincides with an orderly timing change.DacValue 4047, measured value -26.506960 ns...DacValue 500, measured value -1.292715 nsI think I'm on to something here...I tried to post the entire log for the working scope figuring someone might be able to use it in the future to repair their scope, but I got a posting error whine that there was more characters than allowed. 20,000 characters appears to be the limit. That's kinda dumb as the board allows pictures to 1MB.I'll have to find a work-around. Maybe zip it up?

author: Jwalling
author_rank: Unknown
timestamp: August 20, 2016, 07:06:38 pm
content: I've zipped and attached the known good cal log to this message. It's in .txt format so safe for computer consumption.There's a 16 bit DAC: Analog Devices AD7846 This is actually a 12 bit DAC with a small 4 bit DAC controlling a 16 resistor string for the 4 MSBs. Weird, never seen one of these before... It uses a AD780 voltage reference: The AD780 (according to the features) is an ultrahigh precision bandgap reference voltage which provides a 2.5 V or 3.0 V output from inputs between4.0 V and 36 V.Features: (sorry don't know how to do special characters)Ultralow Drift: 3 ppm/ degree C maxHigh Accuracy: 2.5 V or 3.0 V +- 1 mV max

author: Jwalling
author_rank: Unknown
timestamp: August 20, 2016, 07:31:25 pm
content: Other interesting parts:U1401: National (now TI) LM2306. Blurb:PLLatinum™ Low Power Frequency Synthesizer for RF Personal CommunicationsLMX2306 550 MHz, LMX2316 1.2 GHz, LMX2326 2.8 GHzhttp://www.ti.com/product/lmx2316?keyMatch=lmx2306&tisearch=Search-ENI wonder what function that serves?Generating the clocks for the A/D converters?And you can't look at anything HP/Agilent/Keysight without finding something with a house number. U2201: 1821-0236 LIU a 24 pin SOIC located just behind and outside the CH1 CH2 attenuators. Nothing on Google for that; thought I'd get lots of hits from Asian sellers! Might as well make that my second shotgun attempt unless I can figure out where/what that DAC is driving.I'll probably check the VREF tomorrow. If that looks good, I'll probably shotgun this one and replace the DAC.

author: siggi
author_rank: Regular Contributor
timestamp: August 20, 2016, 08:45:33 pm
content: Hey Jay,Does equivalent time work right on this scope?This is a total WAG, but this could be about the/a trigger time interpolator. I'm not sure how it's done, but the Tek scopes I'm familiar with do some form of calibration of their interpolators. I'm guessing again, but one way to test the interpolators would be to inject a signal with a period synchronous to the sampling clock. By modulating the trigger level, it should be possible to generate triggers at a time that changes monotonically from a sampling clock.Siggi

author: Jwalling
author_rank: Unknown
timestamp: August 21, 2016, 12:01:39 pm
content: Quote from: siggi on August 20, 2016, 08:45:33 pmHi Siggi, thanks for your ideas. I had hoped to do some work on the scope today, but may not be able to after all. I'll give your suggestions a try sometime this week.

author: humgar
author_rank: Regular Contributor
timestamp: December 26, 2018, 12:53:00 am
content: My 54831B recently developed exactly the same problem, after replacing a few failed SMD relays (vertical passes, trigger fails, the log file says it only failed 'pred delay channel 1' like yours).Did you happen to have done the same (reworked the PCB) before you got this cal failure? I'm trying to see if it's a PCB problem or I'll have to nail a worn out IC.Thanks!

author: humgar
author_rank: Regular Contributor
timestamp: December 26, 2018, 06:22:31 am
content: Got it figured out. It's the DG444DY at the bottom side of the board under the metal shield. I figured if we both have this problem, it might be aging, so I moved the chip from the least used Channel 4 to Channel 1 (all the relays in channel 1 of my unit are worn out). Hope this will help other people.

author: rickells
author_rank: Regular Contributor
timestamp: April 15, 2019, 09:34:55 pm
content: Looking for more details on your solution, can you provide them ?thank you,My recently acquired Agilent 54845a has Trigger self-test "Failed" on all three of the Trigger tests; for all 4 channels.My scope does power On & can measure the Sq. wave signal from the Aux Out, Ok, (with knobs twiddled manually).It passes all of the other self-tests, .... just Not the 3 Trigger tests.1) -- How does one fix this problem ??

author: humgar
author_rank: Regular Contributor
timestamp: April 16, 2019, 02:06:51 am
content: 54845A is a completely different beast. Check these out:http://www.dasarodesigns.com/projects/fixing-an-hp-agilent-54845a-infinium-oscilloscope/https://www.eevblog.com/forum/repair/agilenthp-54845a/