voltage regulator testing AND optocoupler

[kardenm]

Can anyone tell me how to test a KA7812, 3-pin voltage regulator transistor?

[lilshawn]

legs go....input, ground, output. (viewed reading printing)

13-30 volts on the first leg

ground to second leg

volt meter black to second leg as well

voltmeter red on third.

if it reads 12 volts your fine.

[kardenm]

Thanks much lilshawn!

Another question; is there a way to test an 'optocoupler' #PC123Y11  ??

[lilshawn]

the PC123Y11 is basically an LED and a light sensitive transistor stuck in a package. there really isn't a foolproof way of being sure it's still good other than replacing it.... you can get a general idea if it's still operational though.

pin 1 (closest to dot marked on package is the anode place your positive power here)
below that is pin 2, (the cathode. place the negitive here)

use a power supply of about 5 volts DC. 500 milliamps. to power the led


place a volt meter on resistance test and measure between pin 3 and pin 4, as you apply and remove the voltage to pins 1 and 2, you should notice a drop and rise in resistance because the light from the LED inside is allowing current to flow through the transistor portion of the chip. if there is no change, likely it's bad. for the small amount the chip costs, it may be just as easy to just replace it and know 100%.

[Kevin Mullins]

I recall reading somewhere about using two meters to do a similar test. One being the power source, like in conitinuity or diode test mode, and the other to read the other side, output. I forget the details now though.

[lilshawn]

I recall reading somewhere about using two meters to do a similar test. One being the power source, like in conitinuity or diode test mode, and the other to read the other side, output. I forget the details now though.

yeh, i remember vaugely something like that, but i figured a 5 volt power supply would be easier than trying to source another volt meter. some people tying to fix issues don't even have 1 (one) to begin with 

BTW, I own 3 fluke meters.... to test voltage and current at the same time...and one just in case.

[kardenm]

Appreciate your help lilshawn.  I did the voltage regulator test and turns out mine is still good.  Worked just like you said. Is that test the same for any similar voltage regulator?

I will try the test on the optocoupler today.  I learned all about that device from wikipedia.  Very interesting. I usually look up any device/component I come across.  It's great resource but doesn't ever give any test procedures.  I really appreciate your willingness to share your expertise.

[kardenm]

lilshawn.

I tried test as you suggested.  I get no change when power is applied to the LED side, resistance meter reads open/over limit. 

I used the power supply from cabinet I have here in the shop (peter chou).  Is it possible this test could damage the optocoupler if the voltage or current is to high.  Mine was putting out 5.1 volts.

[MonMotha]

If you applied a 5V supply with no current limit to that LED, you probably fried it.  You have to limit the current somehow (e.g. current limit on a bench supply or just a resistor).

[Kevin Mullins]

There would be a definite polarity to tit as well, right?
(like any other LED that has a + and a - )

[kardenm]

OOPS.  Then I probably fried it.  I did connect with proper polarity but did not limit the current. 

[MonMotha]

There would be a definite polarity to tit as well, right?
(like any other LED that has a + and a - )

Yeah, but they'll usually handle 5V in the reverse direction without damage since it won't conduct any current (it is still a diode, after all).

[lilshawn]

ya i suggested a 500ma power supply since the diode in the PC123Y11 is capable of handling 6 volts and a peak current of 1000ma with the normal being 50ma. i figure 500ma is fine for a quick test. dumping 35,000 ma from a benchtop supply might be too much for it.

i would just go ahead and replace it.

[kardenm]

Thanks lilshawn. 

I'll have to wait for a replacement but may try swapping one from a good board that I have.  I just don't like messing with a working board.  But, I've alredy swapped a couple other parts to try and narrow this down.