| Electronics > Repair |
| Fluke 87 1st gen. AC and DC Voltage not auto-ranging |
| (1/2) > >> |
| Gary IN:
I got this old Fluke 87 first gen. with the following problems & could use some brain power to fix it. * VDC always displays minus 39V (pic). When I measure 30VDC it will add or subtract only 5V - depending on polarity. * VAC first jumps up and down in the mV range, which seems to look ok, but shows 24.5 VAC when plugged in to 115 VAC outlet. * Diode test shows max (no zero or anything else). _______________________________ Strangely, everything else seems to work OK: mV DC. Ohms, continuity buzzer, Amps, mAmps and microAmps show accurate values. Both fuses were blown when I got it |
| Gary IN:
Any ideas? Schematic pages from the Service Manual attached. |
| dustooff:
Hi, have you tried cleaning the rotary switches? |
| MathWizard:
So it looks like ACV, DCV, DT and Capacitance use mostly the same RC networks and internal switches in the IC. So does capacitance also not work right ? You can check the RC parts around that IC. IDK about these meters, but I'm worried it's those switches inside the chip. |
| Gary IN:
--- Quote from: dustooff on November 18, 2024, 09:13:24 am ---Hi, have you tried cleaning the rotary switches? --- End quote --- I wiped that rotary switch and it is in perfect shape. The readings showing on the display are consistent. Thanks for the suggestion. |
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