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I'm trying to self learn all this stuff as I am a programmer not a engineer by trade So any help will be great.

I have a Samsung TV Model : UA46B7000WF

The Problem is that the TV blew a fuse which i then replaced and then that fuse blew to, so I decided to check the diode on the power board (Image Below) so One Diode Read 465 and One Read 467 so here are the things I am wondering:

  • Has the diode shorted? I was watching a couple of Youtube videos and it said that it should be between 500 and above and other places 400 and below so I am not sure if it has shorted or not

  • Is there some sort of chart available that I can use and learn to check what each diode, register, capacitor should read on a Multi Meter? I am trying to learn and understand any good learning resources will be great

Thanks

Samsung Power Board Image

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  • \$\begingroup\$ If you are measuring this in situ without removing the part it is impossible to give an answer without a schematic. There may well be another path between the two nodes. \$\endgroup\$
    – crasic
    Dec 8, 2015 at 5:19

4 Answers 4

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The answer depends on the type & condition of the diode you measure. Typically, a good, forward-biased silicon diode will have a voltage drop measurement of 0.5V to 0.8V.
A good, forward-biased germanium diode will have a voltage drop measurement of 0.2V to 0.3V.

It's usually best to test the diode out of circuit.
You should also test the diode in both directions to ensure that it blocks current in one direction (i.e. shows no voltage drop (i.e. 0V) when the diode is reversed-biased).

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Hope this helps : It shows how to test diodes using multimeter and gives sufficient details too.

http://en-us.fluke.com/training/training-library/test-tools/digital-multimeters/how-to-test-diodes-using-a-digital-multimeter.html

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You need to add units. The multimeter read 465 what? Ohms? mA? Volts(Hopefully not)? Did you measure with respect to ground or across the terminals?

The typical voltage drop across a diode is usually around .6 Volts and will vary depending on many factors such as temperature and diode type. This means that a properly working diode should have a small voltage (around .6) when you measure across the two terminals in the forward direction. If by shorted you mean the internals of the diode are shorted then you should not get any reading on the multimeter at all since the two terminals would be definitionally at the same potential. Again though it is hard to say because you did not label the units.

There are many products that have specifications reports that give voltages for test points and such for specific cases like yours, but I don't think that you'll have an overwhelming amount of luck finding one for a TV. If you are confident in your abilities then you can try to diagnose and repair the issue yourself, but if you are not experienced with electronics I would highly recommend having it repaired professionally or at the very least have someone with experience help you. I would not go probing around with anything in a TV unless you have a strong electronics background and even then you should take caution. Please be safe.

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  • \$\begingroup\$ On the Multi Meter it was Diode Test mode \$\endgroup\$
    – knight
    Dec 8, 2015 at 5:05
  • \$\begingroup\$ Did you isolate at least one terminal from the rest of the board before testing it? \$\endgroup\$
    – user92289
    Dec 8, 2015 at 5:09
  • \$\begingroup\$ No I did not, how would i go about doing that? \$\endgroup\$
    – knight
    Dec 8, 2015 at 5:21
  • \$\begingroup\$ @Ash: You would melt & remove the solder from one of the ends of the diode & lift it out of its mounting hole so it is free from the circuit board. Then put your meter in diode mode & place the meter's positive probe lead on the diode anode (+) and the meter's negative probe lead on the diode cathode (-) (which is the end of the diode body that usually has a silver ring around the body of the diode see here: 31.media.tumblr.com/tumblr_lgn9l9OWCF1qf00w4.png \$\endgroup\$
    – zeffur
    Dec 8, 2015 at 5:38
  • \$\begingroup\$ You don't necessarily need to remove if you are able to turn the TV on while testing, but if you are unable to keep the TV powered then you should follow zeffur's instructions to test each diode. \$\endgroup\$
    – user92289
    Dec 8, 2015 at 18:08
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With regard to readings obtained when testing diodes/rectifiers using the Diode Test Range of a multi-meter, it should be noted that semi-conductor devices are considered to be non-linear in terms of resistance.

The same diode measured on different instruments is likely to give differing results since the reading will depend to some extent, on the level of test current output by the multi-meter.

The reading obtained will be the forward voltage drop in mV and will vary by type of device and ambient temperature, as other contributors have indicated.

In the vast majority of circuits, the difference in reading between a forward and reverse biased 'healthy' diode is generally so great as to enable GO/NOGO checks to be carried out with the device in-circuit, but unpowered of course!

The base-emitter and base-collector junctions of bipolar transistors may be similarly GO/NOGO checked.

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