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Agilent 54835A scope (4 channel 1GHz / 4Gs/s) repair & uphack
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nctnico:
Today I ran the calibration procedure (again because the calibration data from yesterday somehow got lost). According to the log it seems the attenuator for channel 4 (which used to be on channel 2 which was defective) is a little bit off for the 1x (1.024) and 5x (5.092) settings.
Jwalling:

--- Quote from: nctnico on July 14, 2017, 11:23:26 pm ---Today I ran the calibration procedure (again because the calibration data from yesterday somehow got lost). According to the log it seems the attenuator for channel 4 (which used to be on channel 2 which was defective) is a little bit off for the 1x (1.024) and 5x (5.092) settings.

--- End quote ---

A long-shot, but what if you config back to 54835A?
nctnico:
I'm more inclined to swap the attenuators but the error is so small I don't think it is worth the effort. BTW this is a picture showing the input path (from the help file I found):


These are the calibration results

--- Code: ---1)
Hf Attenuators:         Passed                                             
         0.991           4.968          10.002          50.212             

2)
Hf Attenuators:         Passed                                             
         0.996           4.988          10.009          50.148             

3)
Hf Attenuators:         Passed                                             
         0.994           4.985          10.000          50.114             

4)
Hf Attenuators:         Failed                                             
         1.014           5.092          10.000          50.000             

--- End code ---
Channel 4 is clearly different but the error is less than 2%. Maybe channel 2 got overloaded which damaged the attenuator and destroyed the ADC hybrid.
Jwalling:
I have an entire ACQ board (unknown status, missing all the A/D converters and has one attenuator module which is known to be bad) Do you think you could use any parts from it? You could have the attenuator module for the cost of shipping.
Some of those Teledyne relays have resistor(s) inside, maybe the one that was overloaded increased the resistance on one of them?
nctnico:
Tempting but I think I'll leave it like it is for now. Also shipping costs may be getting close to buying a new relay if one of them turns out to be bad. I see no obvious resistive divider structures so I guess the attenuation network is inside the relay.
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