Does anyone have familiarity with the repair of either the Agilent 34410A or the 34401A? I am in the process of repairing an Agilent 34410A DMM which is giving faulty readings on 2-wire ohms. All other functions appear to be accurate and stable.
When I measure 2-wire ohms I get an offset in the reading. For example on the 100 ohm range I will get readings from 102-110 Ohms in 2-wire mode when measuring a 100 ohm resistor. This same resistor measures a stable 100.0 ohms on a known good meter. In 4-wire ohms mode, the meter under repair gives an accurate stable reading of 100.0 ohms. The current source for 2-wire ohms (100 ohm range) is a stable 1010 microamps on the faulty meter versus 1007 microamps on a known good 34401A.
Also, the 2-10 ohms offset appears to drift over time. The same behavior occurs regardless of whether the probes are connected to the front or rear terminals. Multiple sets of probes were used and all gave similar offset. On a known good meter the probe resistance was measured to be 0.2 ohms and stable; multiple probe sets were tried. So far I have checked the relays that switch the signal paths and they appear to be ok (no offset detected across any of the closed contacts). The offset must be coming from elsewhere in the signal path.
The unit was purchased new in Nov. 2006. Agilent does not offer repair of this model, they only offer $727 swap of the faulty unit with a refurbished unit.
Any help/advice would be much apprecaited!
Jeff
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