Sometimes knowing what something means is half the battle. Agilent 54831B error.

[Jwalling]

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 errors
Pred Delay

Looking 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: [Select]

Starting ---- Pred Delay Chan 1 ----                                                 

       PredII Delay:                                                                 

DacValue 4047, measured value -13.353395 ns                                         

DacValue 4044, measured value -13.341964 ns                                         

DacValue 4041, measured value -13.351937 ns                                         

DacValue 4038, measured value -13.339552 ns                                         

DacValue 4035, measured value -13.332947 ns                                         

DacValue 4032, measured value -13.353590 ns                                         

DacValue 4029, measured value -13.354949 ns                                         

DacValue 4026, measured value -13.360570 ns                                         

DacValue 4023, measured value -13.336095 ns                                         

DacValue 4020, measured value -13.349425 ns                                         

DacValue 4015, measured value -13.347497 ns                                         

DacValue 4010, measured value -13.336314 ns                                         

DacValue 4005, measured value -13.343502 ns                                         

DacValue 4000, measured value -13.341724 ns                                         

DacValue 3990, measured value -13.343192 ns                                         

DacValue 3980, measured value -13.344093 ns                                         

DacValue 3970, measured value -13.341962 ns                                         

DacValue 3960, measured value -13.345629 ns                                         

DacValue 3940, measured value -13.362776 ns                                         

DacValue 3920, measured value -13.340799 ns                                         

DacValue 3900, measured value -13.350159 ns                                         

DacValue 3850, measured value -13.340446 ns                                         

DacValue 3800, measured value -13.356761 ns                                         

DacValue 3700, measured value -13.336536 ns                                         

DacValue 3600, measured value -13.353269 ns                                         

DacValue 3500, measured value -13.349758 ns                                         

DacValue 3400, measured value -13.326202 ns                                         

DacValue 3300, measured value -13.334139 ns                                         

DacValue 3200, measured value -13.346145 ns                                         

DacValue 3100, measured value -13.345421 ns                                         

DacValue 3000, measured value -13.349342 ns                                         

DacValue 2500, measured value -13.342110 ns                                         

DacValue 2000, measured value -13.349216 ns                                         

DacValue 1500, measured value -13.351903 ns                                         

DacValue 1000, measured value -13.340774 ns                                         

DacValue  500, measured value -13.357989 ns                                         

Predator Clock had 36 points
                                                       

Not enough points to cover to -5.000000e-009
                                       

>>Time 6 Seconds                                                                     

Finished ---- Pred Delay Chan 1 ---- FAILED
It 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.

[Jwalling]

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.

[Jwalling]

Here's the relevant section of the cal log from a working 54831B that is now a 54832B

Code: [Select]

Starting ---- Pred Delay Chan 1 ----                                                 

       PredII Delay:                                                                 

DacValue 4047, measured value -26.506960 ns                                         

DacValue 4044, measured value -25.140730 ns                                         

DacValue 4041, measured value -23.837760 ns                                         

DacValue 4038, measured value -22.617230 ns                                         

DacValue 4035, measured value -21.569417 ns                                         

DacValue 4032, measured value -20.556526 ns                                         

DacValue 4029, measured value -19.718843 ns                                         

DacValue 4026, measured value -18.904307 ns                                         

DacValue 4023, measured value -18.169278 ns                                         

DacValue 4020, measured value -17.461358 ns                                         

DacValue 4015, measured value -16.454694 ns                                         

DacValue 4010, measured value -15.536123 ns                                         

DacValue 4005, measured value -14.709744 ns                                         

DacValue 4000, measured value -13.974669 ns                                         

DacValue 3990, measured value -12.731329 ns                                         

DacValue 3980, measured value -11.677745 ns                                         

DacValue 3970, measured value -10.784454 ns                                         

DacValue 3960, measured value -10.029580 ns                                         

DacValue 3940, measured value -8.852160 ns                                           

DacValue 3920, measured value -7.897604 ns                                           

DacValue 3900, measured value -7.146338 ns                                           

DacValue 3850, measured value -5.791833 ns                                           

DacValue 3800, measured value -4.935967 ns                                           

DacValue 3700, measured value -3.817691 ns                                           

DacValue 3600, measured value -3.138679 ns                                           

DacValue 3500, measured value -2.709593 ns                                           

DacValue 3400, measured value -2.434677 ns                                           

DacValue 3300, measured value -2.234768 ns                                           

DacValue 3200, measured value -2.034764 ns                                           

DacValue 3100, measured value -1.882188 ns                                           

DacValue 3000, measured value -1.753784 ns                                           

DacValue 2500, measured value -1.424039 ns                                           

DacValue 2000, measured value -1.303628 ns                                           

DacValue 1500, measured value -1.279799 ns                                           

DacValue 1000, measured value -1.301880 ns                                           

DacValue  500, measured value -1.292715 ns                                           

Predator Clock had 36 points
                                                       

Max curve fit error 97ps at 5ns                                                     

Section 0 -5.000000e-009 Clk cal 1st Order Term 4.049588e+003                       

Section 0 -5.000000e-009 Clk cal 2nd Order Term -1.018690e-006                       

Section 0 -5.000000e-009 Clk cal Offset    Term 8.200001e-010                       

Max curve fit error 23ps at 10ns                                                     

Section 1 -1.000000e-008 Clk cal 1st Order Term 4.093055e+003                       

Section 1 -1.000000e-008 Clk cal 2nd Order Term -1.249050e-006                       

Section 1 -1.000000e-008 Clk cal Offset    Term 6.600001e-010                       

Max curve fit error 23ps at 10ns                                                     

Section 2 -1.500000e-008 Clk cal 1st Order Term 4.095291e+003                       

Section 2 -1.500000e-008 Clk cal 2nd Order Term -1.261547e-006                       

Section 2 -1.500000e-008 Clk cal Offset    Term 7.200001e-010                       

Max curve fit error 62ps at 14ns                                                     

Section 3 -2.000000e-008 Clk cal 1st Order Term 4.105554e+003                       

Section 3 -2.000000e-008 Clk cal 2nd Order Term -1.631854e-006                       

Section 3 -2.000000e-008 Clk cal Offset    Term -1.590000e-009                       

Max Data Dac Setting 4080                                                           

Data Delay Value for [0], 26.506960ns, 4042                                         

Data Delay Value for [1], 25.140730ns, 4038                                         

Data Delay Value for [2], 23.837760ns, 4034                                         

Data Delay Value for [3], 22.617229ns, 4033                                         

Data Delay Value for [4], 21.569416ns, 4029                                         

Data Delay Value for [5], 20.556525ns, 4025                                         

Data Delay Value for [6], 19.718843ns, 4022                                         

Data Delay Value for [7], 18.904307ns, 4018                                         

Data Delay Value for [8], 18.169278ns, 4017                                         

Data Delay Value for [9], 17.461359ns, 4013                                         

Data Delay Value for [10], 16.454694ns, 4006                                         

Data Delay Value for [11], 15.536123ns, 4001                                         

Data Delay Value for [12], 14.709744ns, 3997                                         

Data Delay Value for [13], 13.974669ns, 3990                                         

Data Delay Value for [14], 12.731329ns, 3978                                         

Data Delay Value for [15], 11.677745ns, 3969                                         

Data Delay Value for [16], 10.784453ns, 3957                                         

Data Delay Value for [17], 10.029580ns, 3946                                         

Data Delay Value for [18], 8.852161ns, 3922                                         

Data Delay Value for [19], 7.897604ns, 3901                                         

Data Delay Value for [20], 7.146339ns, 3877                                         

Data Delay Value for [21], 5.791833ns, 3818                                         

Data Delay Value for [22], 4.935967ns, 3762                                         

Data Delay Value for [23], 3.817691ns, 3638                                         

Data Delay Value for [24], 3.138679ns, 3498                                         

Data Delay Value for [25], 2.709593ns, 3370                                         

Data Delay Value for [26], 2.434677ns, 3229                                         

Data Delay Value for [27], 2.234768ns, 3066                                         

Data Delay Value for [28], 2.034764ns, 2917                                         

Data Delay Value for [29], 1.882188ns, 2733                                         

Data Delay Value for [30], 1.753784ns, 2457                                         

delta Pts 5                                                                         

Max curve fit error 32ps at 2ns                                                     

Section 0 -5.000000e-009 Clk cal 1st Order Term 4.070445e+003                       

Section 0 -5.000000e-009 Clk cal 2nd Order Term -1.218494e-006                       

Section 0 -5.000000e-009 Clk cal Offset    Term 9.800001e-010                       

Max curve fit error 60ps at 8ns                                                     

Section 1 -1.000000e-008 Clk cal 1st Order Term 4.099052e+003                       

Section 1 -1.000000e-008 Clk cal 2nd Order Term -1.438176e-006                       

Section 1 -1.000000e-008 Clk cal Offset    Term 6.600001e-010                       

Max curve fit error 171ps at 14ns                                                   

Section 2 -1.500000e-008 Clk cal 1st Order Term 4.088170e+003                       

Section 2 -1.500000e-008 Clk cal 2nd Order Term -1.223074e-006                       

Section 2 -1.500000e-008 Clk cal Offset    Term 1.460000e-009                       

Max curve fit error 399ps at 18ns                                                   

Section 3 -2.000000e-008 Clk cal 1st Order Term 4.107018e+003                       

Section 3 -2.000000e-008 Clk cal 2nd Order Term -1.804192e-006                       

Section 3 -2.000000e-008 Clk cal Offset    Term -1.580000e-009                       

>>Time 145 Seconds                                                                   

Finished ---- Pred Delay Chan 1 ---- PASSED 
The 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 ns                                           

I 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?

[Jwalling]

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 between
4.0 V and 36 V.
Features: (sorry don't know how to do special characters)
Ultralow Drift: 3 ppm/ degree C max
High Accuracy: 2.5 V or 3.0 V  +- 1 mV max

[Jwalling]

Other interesting parts:
U1401: National (now TI) LM2306. Blurb:
PLLatinum™ Low Power Frequency Synthesizer for RF Personal Communications
LMX2306 550 MHz, LMX2316 1.2 GHz, LMX2326 2.8 GHz
http://www.ti.com/product/lmx2316?keyMatch=lmx2306&tisearch=Search-EN

I 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.

[siggi]

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

[Jwalling]

Hey Jay,

Does equivalent time work right on this scope?

Siggi

Hi 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.

[humgar]

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!

[humgar]

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.

[rickells]

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 ??

[humgar]

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/