| Electronics > Repair |
| [SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621 |
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| Samogon:
If current source opamp is kaput, sometime you can measure voltage between pins 2-3 and 5-6 of u201 Should be zeros. If not, change opamp |
| abnormalalien:
Yes, it does seem to be the case that there's something off at U201 (see attached schematics with measured voltages in green). However, there is also a problem with the input voltage to the op amp. Instead of 7V, I'm getting around 3-4V. I've tried following the schematics to find out where the 7V comes from but I couldn't find it. Any ideas where that comes from so I can trace what's wrong there? Thanks! |
| Zucca:
Nice! We are talking the same language see... a little bit of effort and you are with us.... very cool. Again a shot U201, replace it. Regarding the 7V, anything getting hot on the board? It could be a bad device (maybe U201?) pulling down the 7V rail. --- Quote from: abnormalalien on May 29, 2018, 02:40:52 pm ---I've tried following the schematics to find out where the 7V comes from but I couldn't find it. Any ideas where that comes from so I can trace what's wrong there? --- End quote --- In the manual sheet 5 of 8, 9-12, page 160 of 165 in the pdf here: https://www.keysight.com/upload/cmc_upload/All/34401-90013-mla2.pdf there is a nice page with title REFERENCES: 7V is generated by U400-B. I did spent 5 minute on this so sorry if I was wrong... but it should help you anyway. EDIT: Yes the 7V are 1:1 the output from U403 (LM399). The U400-A takes the 7V from there to the U400-B which is just a buffer for the rest. ahhh look here too: https://www.eevblog.com/forum/repair/repairing-an-hp-34401a-dmm-51092/msg714640/#msg714640 EDIT2: check the supply voltage rails 15V/18V for the OPAMPs too.. just to make sure... |
| abnormalalien:
Excellent, thank you! I was completely skipping over the word References in favor of the schematic titles at the bottom right. I will check out this one next! I am still a bit confused about ground. Earlier, I mentioned my advisor said I should be able to directly measure voltages by putting lo at case ground and high at whatever pin/location I'm trying to measure. I tried that and it did not work; everything around U201 was 0V. Then I checked: the resistance between case ground and the white line behind the display ribbon is OVLD. Thus, I've been using the white line. On the power schematics, this is labelled GND. But on the References (AD Converter) and the Ohm's supply schematic, many of the grounds are labelled AGND (analog?). Can I still use the white GND line or is there another ground that is more appropriate for AGND labels? |
| Kleinstein:
For most measurements (especially DC volts) in the analog part the common input terminal should be a sufficient ground point. The outer case is connected to protected earth and the interfaces and digital section. So there are two essentially isolated parts. |
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