Fluke 87IV has high error with 50mV and 500ohm Ranges

[rniu]

I got one used 87-IV DMM. After calibrated it with Fluke 5500A, I found there's a couple of mV error on DCV range even if I shorted the inputs. Then I redo the calibration, the 50mV range looks no good as I see the last 2 and even 3 digts changes a lot. Also notied the ohm range always have 4-6 ohm reading if I short the input terminals. If I short the terminals, the 50mV range also shows about 0.3mV offset. I have tried soaking the board into alcohol for 2 days and bake one night with 70C. It didn't work.

Appreciated if any inputs.

Thanks!

[rniu]

To describe more details: On mV range, the shorted results is 0.3xx mV. Then switch to Ohms range, the shorted reading is 3.xx ohms. If switch to other Ohms range manually, every range will show 003x offset even in Kohms, Mohms ranges. It looks like a consistent offset always. I have put the board into alcohol over 24 hours for twice. Didn't help.

[Ugur]

If you are sure that the internal resistance of the shorted test lead is low, you can try to do the adjustment calibration.

[srmahaffy]

Hi, make sure the “com” port and the “V” ports are clean, and that the test leads are seated well. You can also check the continuity between each port, and its solder pads, to make sure you have good continuity. If not, try cleaning, and reflowing the solder pads.
Use Isopropyl alcohol 70% or 91% to clean the ports and solder residue on the PCB, (if you do any soldering). Also, are you sure your test leads are good? Let us know how things are going.

[srmahaffy]

Sorry, I overlooked your information on your use of Isopropyl alcohol and baking. Check the continuity of each of the meters ports to the PCB.