I say again that DMM's canno't and are not able to accurately "load" a forward biased junction that has gone faulty. Without the obvious 'no beep" as in open or "beeeeep" as in shorted junction. That's it. Absolutely nothing in between.
Hey and Hi. You are using DMM's to test the "current flow" through a forward biased Semiconductor junction as per above.
I say again that DMM's canno't and are not able to accurately "load" a forward biased junction that has gone faulty. Without the obvious 'no beep" as in open or "beeeeep" as in shorted junction. That's it. Absolutely nothing in between.
Take it for the truth that an Analogue meter NEVER lies when testing forward biased junctions. Use it on X1 on Ohms and learn to know the Analogue meter with readings on good junctions that are forward biased by your Meter. The meter can be a cheap Analogue. You will pick up very quickly when a junction looks suspect.
Maybe you should explain what you mean when you say "load" a forward biased junction. What an analog ohmmeter does is pass a current through the junction, and that's the same thing a DMM does.
Furthermore, when using a DMM to test a junction, one shouldn't just rely on a "beep". The meter will indicate the forward bias voltage across the junction when it carries the milliamps current put out by the DMM. That voltage varies with the condition of the diode--shorted, open, damaged or in good condition; for example, you can tell the difference between a Schottky and a non-Schottky easily.
You say there's "Absolutely nothing in between"; this is not true. The forward voltage of the diode is shown by the DMM, and this is same information you get with the ohms function of an analog meter. The analog ohms range just doesn't indicate the forward voltage directly, but you can learn, as you obviously have, to interpret the ohms reading. A DMM's reading of the forward voltage gives the same information. The ohms reading on an analog meter doesn't tell you any more than knowing the forward voltage does; it's telling you the same thing in a different format.
DMMs don't "lie" either; they tell you what the voltage across a junction is when it's forward biased with a few milliamps. You don't just rely on "beeps; you look at the value of the forward voltage. It's not just a matter of a beep or no beep. It's not true that there's "Absolutely nothing in between." There's a forward voltage reading. This reading gives the same information as the reading on the ohms scale of an analog meter. It tells you the voltage drop across the forward biased diode, which is the same information an ohmmeter gives you. The ohmmeter converts it to an ohms reading, but it's the same information.
One can just as easily "learn to know" the DMM with "readings on good junctions that are forward biased" by the DMM.
Another thing I may as well say. I am not posting this to try and look smart.
Hey, I'm just intrested in knowing if the old Analog multimeters are still useful.
Please list popular uses and why it's surperior to Digital ones.
I thought Digital was more accurate than analog. The only thing I can think of is that Analog would be more sensitive?
However, let's face it in that a DMM does offer greater accuracy and resolution (resolution being the ability to read the instrument or of the instrument to be read).
...the Fluke on "beep" for good or bad junctions.
A little "loading" goes a long way to checking a Forward biased junction for possible failure/problems.
Problem is the 1N4001 supplying the Frame IC stops conducting and simply goes open......A YEW reveals it.
A Digital Meter does not.
You say the diode goes open. If it's open, there is no question of whether it shows damage if the forward biased direction--it's simply open; no conduction in either direction. If your digital meter can show any indication at all of a 1N4001 that is good (in the forward bias direction), then it can distinguish between a 1N4001 that is open and one that is not.
Does your digital meter show any indication at all with a known good 1N4001? If it does, then it can reveal an open 1N4001. If it doesn't, then get a better digital meter.
You are talking in riddles.
Regards,
tvtech
While I think tvtech is rather overstating the difference, I fully agree that analogue meters are FAR better for testing semiconductor junctions (and old Avometers particularly), simply because they put a reasonable amount of current through the junction.
However, he seems a bit 'confused' about his frame problems?
The 1N4001 isn't 'feeding the frame', it's the bootstrap diode (a 1N4001 isn't fast enough to be the rectifier feeding the frame from the LOPT), and I can't envisage any reason for testing it on ohms?, you would simply measure the voltage either side of it (or check with a scope).
The Electrician
Regarding your post above I believe I explained all questions in your post above three years ago. I use my Fluke 75 for new projects. I use my YEW for repair work. You will not find my Fluke on my repair bench.
The 1N4001 diodes mentioned above read fine with any Digital Meter. Never mind a Fluke. Forward bias is correct and no leakage reversed biased.....
Very old thread here...but nevertheless...
Lately, Frame IC's that "appear to have failed". Problem is the 1N4001 supplying the Frame IC stops conducting and simply goes open......A YEW reveals it.
A Digital Meter does not. My "Technician" was replacing and repeatedly changing the Frame IC....like normal. Spares wasted. Till I showed him
Now, he is clever again. Until the next time. Now every TV with a Frame problem....Automatically...the Diode is changed. Faulty or not.
LOL
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