EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Warsp on October 10, 2023, 11:38:03 pm
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Hello.
I got a supposedly functioning hp3478a multimeter off of ebay the other day and it appears to have some issues. First off, all of the functions are off by some amount. The dc volts range is usually off by around 2. In addition, the 2 wire resistance measurement is always overloaded, and it causes all of the other functions to have a extra high reading when deselected. I have not replaced any of the capacitors yet, but all of the power supply voltages are fine and the calibration data is still intact. I looked in the service manual and found that the U102 hybrid ic may be broken, which is completely unobtainable. Are there any other possible culprits for this issue or should I just buy another meter and pray that it has a working hybrid ic.
-Warsp
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As a base-line, can you confirm:
a. that the meter boots with "SELF TEST OK"?
b. that the front/rear term button (next to the current terminal) is pushed out?
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The meter passes self test and the front rear switch is out. The auto zero and auto/manual buttons also didn't fix anything.
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Good news! I got the meter to correctly measure voltage by using the rear connections. Resistance is still a little off, but it seams like it probably isn't the hybrid ic ;D. I am going to try an clean the switches and hopefully get the front connectors working.
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Definitely clean the snap action switch that selects rear/front inputs. Those types of switches easy get dirty over time and can cause all kinds of strange symptoms. I have this meter and it still works great. Yours will likely require some calibration (as did mine. I grabbed it off eBay as well). But the manual provides detailed calibration procedures.