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Agilent 34401A Bubble on PCB ... can it be saved ? (SOLVED)
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m k:
Some joints in between bad ones seem to be fine.

Kleinstein:

--- Quote from: The_Spectrum.A_idiot on September 13, 2024, 05:23:17 pm ---If you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges?
-- What do you mean exactly ? IF the instrument measures the proper value of a plugged in resistor ? no. not at all. you want me to plug a multimeter in mA mode and measure the output current between the LOW + and - ?

--- End quote ---
Yes use a different DMM (could be even handheld, no high accuracy needed) and measure the current between the COM and +input, when in the different ohms ranges. Ideally this could be 4 wire mode, but 2 wire mode would likely give the same result.

If there is a defect, the current is often way off, like essentially not current. The results can give more of a hint on where the problem is.

Though likely not a problem, another simple test is to check for the input bias current in voltage mode. To high a current there can also cause trouble in the resistance measurements. For a final check of the meter one should do that test anyway. For this test there are 2 ways: the simple is uning the 10 M input resistance mode and something like manual 1 V range to compare the reading with a short and open input. The difference should be well less than some 50 pA*10 M = 500 µV.
The_Spectrum.A_idiot:

--- Quote from: Kleinstein on September 13, 2024, 06:15:26 pm ---
--- Quote from: The_Spectrum.A_idiot on September 13, 2024, 05:23:17 pm ---If you select 4W Ohm, do you measure the appropriate test currents out of + Input and - Input for the different (manually selected) ranges?
-- What do you mean exactly ? IF the instrument measures the proper value of a plugged in resistor ? no. not at all. you want me to plug a multimeter in mA mode and measure the output current between the LOW + and - ?

--- End quote ---
Yes use a different DMM (could be even handheld, no high accuracy needed) and measure the current between the COM and +input, when in the different ohms ranges. Ideally this could be 4 wire mode, but 2 wire mode would likely give the same result.

If there is a defect, the current is often way off, like essentially not current. The results can give more of a hint on where the problem is.

Though likely not a problem, another simple test is to check for the input bias current in voltage mode. To high a current there can also cause trouble in the resistance measurements. For a final check of the meter one should do that test anyway. For this test there are 2 ways: the simple is uning the 10 M input resistance mode and something like manual 1 V range to compare the reading with a short and open input. The difference should be well less than some 50 pA*10 M = 500 µV.

--- End quote ---
With a Fluke 117
At A mode DC and AC I get nothing on the 2 jacks HI-LO going though all ranges of 2W AND 4W MODE
AT mV DC I get nothing on 2 jacks high and low both on 2W and 4W mV AC I get a fixed 150-80mV AC I will get my better meter 287 and I will retry.
The_Spectrum.A_idiot:
Okay good news .

After re-touching the CR203 Q201 and Q202 Continuity is perfect know , Diode mode has issues show 0.4 instead of 0.6V F-v of a diode

So I think it's safe to retouch everything with A LOT of flux and see how it goes.

Thanks
Kleinstein:
The current to look at from the ohms source should be DC from 0.5 µA to 1 mA, depending on the range. Beside the current source part, that is also a chance that a realy is at fault. One could check this by taking the current off CR202 instead of the + input.

No current may also be faulty fuse at the external DMM - so maybe check the continuity.

The already "repaired" area needs to be cleaned anyway - so a touch-up with new flux can be worth a try.

If the resoldering changes things it may be woth to re-measure the voltages (to GND) at Q202, e.g. in the 1 K range, both with the terminals open and shorted. This should give a good idea if the issue is more with the actual current source of the protection.
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