Multimeter problem

[techie_maria]

Hi everyone,

Im a newbie with this kind of stuff. Someone at work gave me a multimeter. He told me theres something wrong with it and I can try fix it myself. Trouble is I dont have a clue where to start hahaha. Anyway, every time I turn it on whether its connected to something or not it seems its not detecting anything and its somehow reading something but its start from 0 to whatever reading increasingly and slowly LOL. It doesnt change at all.
thanks.

its a megger m7027  multimeter.

[robrenz]

Here is the manual . 

[Wytnucls]

Not much you can do.
Make sure there is a fresh battery in it. Open it up and look for signs of damage on the PCB.
Also look at your probes and try another set if you think the original ones may be damaged, or have loose connections at the jacks.

[PA0PBZ]

When you turn it on by just turning the big button one click it will be in AC volts measurement, and since these things are quite sensitive it is not strange that something shows up on the display. However, with the test leads in the two right most sockets and then touching the pins together it should read almost zero. Now click the big button one step further and it should be in DC volts, and you should be able to measure a battery.

Any luck with that?

[6502nop]

Using the manual robrenz posted, skip to page 31 of the pdf (page 56/57 of the manual, section VII: Maintenance), and follow the proceedure to replace the 9V battery. While there, check the fuses.

Yes, this means you'll need a second meter. You didn't provide your location, but even the extremely cheap and disliked meter from Harbor Freight here in the USofA will do. Maybe your friend can let you borrow his/her new meter for a day or two.

If the fuses pass, then you'll need to pick up some components to measure to see how far off your meter is. You'll also need a second meter for this, to give you a baseline value for each component. Since this meter has full-scale values of 4xxxx, I'd suggest staying in the middle by using "22" or "27" values:

22/27 ohm resistor
220/270 ohm resistor
2.2k/2.7k ohm resistor
22k/27k ohm resistor (use this or 220K if you can only get one value)
220k/270k ohm resistor
2.2M/2.7M ohm resistor
22M/27M ohm resistor
9 or 12VDC battery or wall adaptor (check actual voltage with second meter)
Jumper leads (wires with "alligator" clips on each end)

DO NOT try to measure ANY mains voltages until we have this thing figured out! Pictures of the inside would be really nice to have, too.

The resistors will verify each of the ranges of your meter (in ohms setting) are reading correctly. Same with the battery/adaptor voltage. To measure current, just use the 220k/270k in series with the battery and measure with the second meter. Your meter should read about the same. If any of these readings are off, post what you were trying to read, what the good meter read, and what your meter reads:

Code: [Select]

Item                GoodDMM         MyDMM
220K                219.99K         109.49K
12VDC               12.834VDC       6.4170VDC
12VDC/220K (~58uA)  59.016uA        29.231uA
In Dave's videos, he uses a precision reference to do this, but we're just seeing what's going on with the meter, so we don't need this kind of precision (just yet). Even the previously mentioned Harbor Freight meter can get you down to less than 3% accuracy. For most young players, this is pretty darned good.

If you want to go the extra mile and measure capacitance, frequency, or conductance and post results here, that's okay - but my guess is that whatever the problem is, it's affecting every range, so solving for the main three should help us zero in on the problem. In the case I present above, we can see that my phantom meter is reading almost exactly half of what it should. This leads us to suspect the meter's reference voltage. If the current was okay, then we'd know the reference was okay, but since the volt/ohm share inputs, we'd start looking there for problems.

nop

[kipp]

The Megger M7027 appears to be almost identical to an Iwatsu VOAC-86.  I have one of the latter that's gone strange and I'm trying to track down a service manual (of it or any of its relatives).  I think the Yokogawa 73301 is another cousin, but it's only 4000 count, not 40,000 count, and has only one row of function buttons below the display.  Yokogawa must have also sold a fancier 40k meter at that time, which would probably again be this meter inside, but I haven't found a model number yet.  Not that any of this has helped me track down a service manual, but I thought I'd mention it in case someone else finds this thread in a few years and it helps them.