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@ -29,9 +29,7 @@ Now, the resistors for this amp seemed to be affecting the pass or fail, replaci
## Replacing the capacitors ## Replacing the capacitors
To save the meter from an early demise, I replaced all the capacitors, and indeed some seemed to be leaking already, I was lucky to replace them before the corrosion got worse. To save the meter from an early demise, I replaced all the capacitors, and indeed some seemed to be leaking already, I was lucky to replace them before the corrosion got worse.
![LeakyCap](3458-WorkLog/imgF.png) Another healthy upgrade I did was to update the firmware to the latest version, which improved the accuracy of the meter to some extent due to the various mathematical updates to said firmware. In the service note [here](3458-WorkLog/SN12C.pdf) one can find the fixes listed. But as a quick overview on some fixes from Rev 4 to Rev 9 are:
Another healthy upgrade I did was to update the firmware to the latest version, which improved the accuracy of the meter to some extent due to the various mathematical updates to said firmware. In the service note [here](/3458-WorkLog/SN12C.pdf) one can find the fixes listed. But as a quick overview on some fixes from Rev 4 to Rev 9 are:
- Revision 8,X: Period measurement correction - Revision 8,X: Period measurement correction
- Revision 7,X: Resets line frequency to 60Hz - Revision 7,X: Resets line frequency to 60Hz
- Revision 6,X: ACV adjustment corrected - Revision 6,X: ACV adjustment corrected
@ -39,8 +37,10 @@ Another healthy upgrade I did was to update the firmware to the latest version,
- Revision 5,X: DCV measurements on the 10 V range were shifted by 0.13 uV (within specifications but slightly biased) - Revision 5,X: DCV measurements on the 10 V range were shifted by 0.13 uV (within specifications but slightly biased)
- Revision 5,X: Sending “AZERO ONCE” does not always cause the 3458A to immediately make the autozero measurement. - Revision 5,X: Sending “AZERO ONCE” does not always cause the 3458A to immediately make the autozero measurement.
![LeakyCap](3458-WorkLog/imgF.png) ![New Cap](3458-WorkLog/Caps.JPG)
## U180 drift evaluation ## U180 drift evaluation
Now the big question with any 3458A project is whether the U180 ASIC at the heart of the meter is still in good condition. This requires an extensive check, powering the meter and monitoring the calibration constants from the ACAL DCV. I have written a toolkit for this. Although this is a rather short data capture, several captures were made. All with similar results in terms of the drift observed. Now the big question with any 3458A project is whether the U180 ASIC at the heart of the meter is still in good condition. This requires an extensive check, powering the meter and monitoring the calibration constants from the ACAL DCV. For this, a toolkit was written. And although this is a rather short data capture, several captures were made. All with similar results in terms of the drift observed.
![u180-drift](3458-WorkLog/U180-drift.png) ![u180-drift](3458-WorkLog/U180-drift.png)
@ -53,7 +53,7 @@ Secondly and majorly is chemical reactions over time, though stable a chip still
And then there is also quite a big contribution from mechanical stress- the LTZ1000 is a silicium die placed in a metal can. Whenever it cools down or heats these two materials will expand and contract at different rates. Causing some stress to be transferred to the die trough the glue holding the two materials together, this creating hysteresis at every powercycle. And then there is also quite a big contribution from mechanical stress- the LTZ1000 is a silicium die placed in a metal can. Whenever it cools down or heats these two materials will expand and contract at different rates. Causing some stress to be transferred to the die trough the glue holding the two materials together, this creating hysteresis at every powercycle.
Thus it is interesting lower the setpoint of the LTZ1000 voltage reference setpoint. Well known on the 3458A is the voltage reference being operated at an extremely high oven temperature. As such I have added a 200K resistor to the voltage reference board at designator X411, decreasing the temperature to about 75degC, giving me a bit more overhead for high ambient temperatures than [traditionally is done](https://xdevs.com/fix/hp3458a/#opt002). Thus it is interesting lower the setpoint of the LTZ1000 voltage reference setpoint. Well known on the 3458A is the voltage reference being operated at an extremely high oven temperature. As such I have added a 200K resistor to the voltage reference board at designator X411, decreasing the temperature to about 75degC, giving me a bit more overhead for high ambient temperatures than [traditionally is done](https://xdevs.com/fix/hp3458a/#opt002).
![ltz-mod](3458-WorkLog/LTZ-MOD.png) ![ltz-mod](3458-WorkLog/LTZ-MOD.JPG)
## Mechanical touchups ## Mechanical touchups
Unfortunately this unit came without pushrods making use slightly more difficult. After unsuccesfully trying to buy some parts from the manufacturer I have decided to design some #D printable ones. To enable hobbyists to repair such missing parts. These will be added in this article later as I finish up the 3D models. Unfortunately this unit came without pushrods making use slightly more difficult. After unsuccesfully trying to buy some parts from the manufacturer I have decided to design some #D printable ones. To enable hobbyists to repair such missing parts. These will be added in this article later as I finish up the 3D models.