DMM output issue

You're not using an LCR meter by any chance?

Jamie

Well, or course, if you have parts installed on the board, then the circuit and parts values determines the resistance that you see between the PCB traces. If you're concerned about the integrity of the PCB itself, then you have to test the board without any components!

I think what he is referring to is the DMM itself is not reading what it should be..

In other words, in the High scale range it is showing what would look like it is far less than 200 ohms, virtually 0 ohms maybe however, in the 200 ohm scale it would then show open.

If he using a LCR meter in the ohms function, he'll get capacitance readings of a function of R. Because most LCR meters I've seen and use has the 1khz-100khz frequency in the test, And for good reason.

Which is the reason i asked this..

Also, it is possible if he is using a basic DMM, the high ranges could be inserting more voltage at the probe and thus seeing other things like conductive settlements on the board left over from a etching process that is possibly producing diode effects that his meter is leeching over to.

Jamie

No, it doesn't. It means that the resistance is above 200 Ohms. No Ohm meter reads infinity, they just indicate 'Out Of Range'.

You aren't using it the right way. You are making a 1:1000 change when you go from the 200 Ohm to 200K Ohm ranges. You go up one decade at a time, not three. Of course it's going to show a low reading when you do it wrong.

You're probably measuring diode junctions inside ICs, not the PCB trace-trace resistance. The 200r range shows a diode as open, probably because it applies a small voltage. The higher ranges apply enough voltage to forward-bias the diodes.

This will vary between meters.

Try reversing the leads, in various cases, and see what happens.

John

Maybe due to voltage compliance changes between the ranges, and the maximum current available also changes.

For diodes, ONLY the lowest range works (is usable) and one needs to try both polarities if diode configuration is unknown.

=A0No

Thanks to each of you for your responses. A few points:

1. I am using a plain DMM, not an LCR meter.
2. The circuit I tested right before my initial post is a simple power supply, with only the capacitors/resistors soldered on, no voltage regulator (LM317 etc.,) I had not even connected the step-down transformer.
3. I am aware that the resistance ranges need to increase in decades -- I was just giving an example.

Therefore my puzzlement.