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Offline alimanTopic starter
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« Reply #160 on: January 26, 2010, 11:39:49 am »
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Thanks Peti80, this is the part that was confusing me. So the Negative(COM)test lead ALWAYS goes to the GROUND pin,  and Positive(V,mA) test lead goes to Output or Input pins.
 Is this procedure the same for both positive and negative regulators?

Thanks, Aliman
Ok now I got it. The 78L12, Input is +9.8V and Output is +8.9V.
                       The 79L05, Input is -8.04V and Output is -3.40V.
 I tried adjusting VR1 , but the highest reading on the Output of 79L05 I could get was -3.4V.
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« Reply #161 on: January 26, 2010, 11:45:19 am »
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I don't like Sad it did you clean the solder side of the board there could be a piece of solder or something sorting the reg that could possibly be the problem or the reg is shot  Angry

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Offline alimanTopic starter
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« Reply #162 on: January 26, 2010, 12:15:42 pm »
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Xavier, it sounds like the 79L05 is SHOT! The output should be close to -5v , Yes?
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« Reply #163 on: January 26, 2010, 12:57:43 pm »
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Yes Aliman but it still bothers me as the one that I had when it was shot did not give out any voltage but you have 3.4v that makes it 1.6v down and it is strange did you look for shorts in fact don't look just brush the board on the solder side with a hard nylon brush also brush the component side with a soft brush there just could be a forint object so small that you will not see it and it could cause a resistance or stray capacitance.

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Offline alimanTopic starter
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« Reply #164 on: January 26, 2010, 12:59:21 pm »
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Also , I checked the solder side of the PCB, all the connections are clean. Cornelus did a excellant job soldering.


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Offline Peti80
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« Reply #165 on: January 26, 2010, 01:09:55 pm »
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Yes, COM is the reference. It measures the voltages relative to that point. So if the red lead is on a higher potential it will display a positive value, if on a lower potential it will display a negative one. If you swap the to leads while measuring the same points, you will get the same value, but with an opposite prefix. (+,-).

The 7905 is not necessarily dead, try removing the output pin from the board (bend it out carefully, if necessary). Leave the input and ground in the board. Try measuring the output now. If you have an output short but regulator is ok, then now you will have 5V coming out. If still only 3V comes out, regulator is dead.

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« Reply #166 on: January 26, 2010, 01:39:06 pm »
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I hope that you have a solder sucker

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« Reply #167 on: January 26, 2010, 02:04:48 pm »
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Ok I have a sucker.I moved the output off the pcb and measured the Output and I got -5.87v.
So it's NOT shot. But connection on the solder side looks good.


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Offline xavier
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« Reply #168 on: January 26, 2010, 02:09:42 pm »
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So I was on the right track YOU must have a short LOOK LOOK LOOK till you find it

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« Reply #169 on: January 26, 2010, 02:30:47 pm »
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I'm lookin and lookin but I can't seem to find the short, where abouts should I concentate my search.?

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