wrong DMM Led diagnostic... - Electronic Circuits Projects Diagrams Free

Zener_Diode · 6th October 2006, 12:04 PM

Hey

VCR philips problem

When I checked the LED with DMM it shows me that the LED is good.
When I replace the old LED by the new one the VCR stated to work properly.
How can it me, the DMM shows that led is good while it is bad???

**Nigel Goodwin** · 6th October 2006, 12:11 PM

Quote:

Originally Posted by Zener_Diode

Hey

VCR philips problem

When I checked the LED with DMM it shows me that the LED is good.
When I replace the old LED by the new one the VCR stated to work properly.
How can it me, the DMM shows that led is good while it is bad???

All the DMM checks is if it's O/C or not - it doesn't mean it actually works!.

Zener_Diode · 6th October 2006, 12:18 PM

Quote:

Originally Posted by Nigel Goodwin

All the DMM checks is if it's O/C or not - it doesn't mean it actually works!.

What is O/C?
How can I check the components and to know that it works for sure?

**Nigel Goodwin** · 6th October 2006, 12:45 PM

Quote:

Originally Posted by Zener_Diode

What is O/C?

'Open Circuit'

Quote:

How can I check the components and to know that it works for sure?

You place it in a circuit and confirm it works correctly, that's the only 100% way.

Tarsil · 6th October 2006, 12:50 PM

Quote:

Originally Posted by Zener_Diode

Hey

VCR philips problem

When I checked the LED with DMM it shows me that the LED is good.
When I replace the old LED by the new one the VCR stated to work properly.
How can it me, the DMM shows that led is good while it is bad???

REading the other post too I'd say that LED doesn't have enought voltage to operate. 1.5V...I haven't seen a LED that can be operated from a single aa batery. So the LED is OK but it doesn't give any light. U should consider replacing the resistor before the led. What value does it has now?

Zener_Diode · 6th October 2006, 02:04 PM

Quote:

Originally Posted by Nigel Goodwin

You place it in a circuit and confirm it works correctly, that's the only 100% way.

It is an infrared LED I can't see it's light.
If I connect it to 10V through 10K resester I have 893uA current, 1V fells on diode.
if I rise the supply voltage the current rise too but the led voltage don't changed.
how can I know that he is good ot bad???

Quote:

Originally Posted by Tarsil

REading the other post too I'd say that LED doesn't have enought voltage to operate. 1.5V...I haven't seen a LED that can be operated from a single aa batery. So the LED is OK but it doesn't give any light. U should consider replacing the resistor before the led. What value does it has now?

I don't remember exactly but I think there was a 76 om resester. 5V before resester and 1.5V on the led. When I put other LED everything started to work properly...
How can u explane this?

HiTech · 6th October 2006, 02:14 PM

Unfortunately, some components may test good under static type testing. However in the dynamic situation (under use/load) the component may act up or not work at all. This is not uncommon.

HarveyH42 · 6th October 2006, 03:48 PM

Quote:

Originally Posted by Zener_Diode

It is an infrared LED I can't see it's light.
If I connect it to 10V through 10K resester I have 893uA current, 1V fells on diode.
if I rise the supply voltage the current rise too but the led voltage don't changed.
how can I know that he is good ot bad???

I don't remember exactly but I think there was a 76 om resester. 5V before resester and 1.5V on the led. When I put other LED everything started to work properly...
How can u explane this?

If you have a digital camera with a preview screen, you can see it light up that way...

Tarsil · 6th October 2006, 09:29 PM

76 Ohms!?

How about puting the LED in series with a 5V PS (could be voltage taken from the VCR), a 150 ohm res and a ampmeter. See the curent drawn by the led.
Also see http://www.gizmology.net/LEDs.htm.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
Am i wrong here	Megamox	General Electronics Chat	18	23rd December 2005 11:55 PM
Onboard diagnostic system help needed	RK NAIR	Electronic Projects Design/Ideas/Reviews	11	18th November 2004 05:28 PM
I must be doing something horribly wrong, SAVE ME!!!	Glyph	General Electronics Chat	0	4th October 2004 03:01 AM
Whats wrong with my code ???	pike	Micro Controllers	10	23rd December 2003 12:58 AM
Hmm what's wrong?	daviddoria	General Electronics Chat	10	27th March 2003 08:25 PM

6th October 2006, 12:04 PM	#1
Zener_Diode	wrong DMM Led diagnostic... Hey VCR philips problem When I checked the LED with DMM it shows me that the LED is good. When I replace the old LED by the new one the VCR stated to work properly. How can it me, the DMM shows that led is good while it is bad???

6th October 2006, 02:14 PM	#7
HiTech	Unfortunately, some components may test good under static type testing. However in the dynamic situation (under use/load) the component may act up or not work at all. This is not uncommon. __________________ Don't make me reach through this monitor to slap you a good one!

6th October 2006, 09:29 PM	#9
Tarsil	76 Ohms!? How about puting the LED in series with a 5V PS (could be voltage taken from the VCR), a 150 ohm res and a ampmeter. See the curent drawn by the led. Also see http://www.gizmology.net/LEDs.htm. __________________ If is too complicated.....most of the times is the wrong way. Last edited by Tarsil; 6th October 2006 at 09:35 PM.