For test purposes, you can use any 1k ohm resistor.
For procurement, see
http://mrmodemhead.com/blog/fluke-87-fusible-resistor/
After replacing the fusible resistor Ohms range worked fine again. However, DCV DCmV and ACV still do the same things e.g.
-- VAC range it oscillates between OL and a value with every display update when probes in Open circuit. Measuring mains voltage displays 146.4V steady (before it was approx 40V and should be 230V here in Spain).
-- VDC displays 352V approx with probes open and
does not goes to zero when shorting probes. However, when measuring a voltage with probes it does adds the voltage and displays 352 + 2/3 measured_voltage (approx).
-- mVDC displays -313mV approx (and sometimes OL) with probes open and
does goes to zero when shorting probes. It also measures spot on (the reference was another fluke 77)
-- Diode Testing OL always, however probes do output 3.81V in Open Loop and source 0.92mA when shorted.
-- Ohms and Current ranges work fine.
Now the imput impedance are the following
VAC OL
VDC 18.75 MOhm with one polarity and 5.6MOhm with polarity reversed
My guess know is the thin film resistor or the main asic might be problem. All sugestions will be appreciated and thanks for helping!
PS, It is amazing the quality of the content ModemHead has in his website. I really appreciate the effort and generosity of this work.