xans/3458A-RepairArticle
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Update 3458A-Repair.md

Browse Source
This commit is contained in:
xans 2024-07-29 00:17:36 +02:00
parent 890b1b015f
commit f14a354f02
1 changed files with 2 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
3458A-Repair.md
View File

@ -5,7 +5,7 @@ This unit has clearly seen better days as the pushrods are gone and it looks pre
[Fix]
On inspection, there are some initial problems that are quite obvious, namely burnt resistors on the main A1 DC measurement board. These have been burned to a crisp, probably due to overvoltage. Looking at the schematics, these are two 10K resistors along the DC input path. Looking at the components, they appear to be CRF65 resistors, very similar to the PTF65. Luckily I had some resistors on hand that could function as a suitable replacement with some artistic creativity. Selftest afterwards reveals seemingly no issue with the DCV section.
![fix](3458-WorkLog/imgA.jpg)
![post fix](3458-WorkLog/imgA.jpg)
![post fix](3458-WorkLog/imgB.jpg)
## AC trouble
Great! Having sorted out the DCV section so easily, I can now move on to the next error the meter displays on power up; Error 202, Hardware failure - AC board. My clue here is that I don't hear any clicking relays and the fault seems to happen almost instantly. This leads me to suspect that the fault is gitial in nature. Troubleshooting reveals that fuse F701 has blown and the meter now has no 14V supply rail on the AC board. Fixing this by inserting one of the spare fuses allowed me to move on, but the error still persisted.
@ -23,4 +23,4 @@ For calibration, the multimeter was first calibrated at home and then taken to a
Once the unit was back home, ACAL ALL was run at various points during the drift evaluation, and it was found that the 204 flatness dac error returned when the ambient temperature became too high. This indicates that the error has not yet been found correctly.
## 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 (linked here). Although this is a rather short data capture, several captures were made. All with similar results in terms of the drift observed.
[imp u180-drift].
![u180-drift](3458-WorkLog/U180-drift.png).