I measured the top of U5 pin, the one closest to the power adapter jack and it got .002. That was with the black to the ground on the source input and the red to the pin on the U5. That means that is the pin that needs the 20 volts I was getting with the D3 band right? WHAT CAN I DO! Doesn't this mean the U5 is a bad batch or what?
Just filled in the holes on each of the D series of things and it didn't help anything. Darn! You mean the hole that the pin on the banded D3 goes into is square right and solder that so that it is closed instead of open right? It didn't do anything! I'm telling you, there is no trace that goes from the D3 to any of the U5 pins. There is nothing that connects the D3 to U5 in regards to the lighter colored green line inside the board trace if that is what you mean. Can I try connecting the banded end of D3 to a pin on the U5 via a hookup wire?
So yes, if you are measuring .002 ohms between ground (black lead on the gain switch shell) and the pin of U5 closest to the on/off switch (red lead there), then that isn't right. That would say there is a short to ground on that trace. HOWEVER - are you sure that you have your meter on resistance and not voltage, and that the O2 is unplugged from the power adaptor? Usually the resistance of the test lead themselves, if you just connect the tips together, are around 0.1 ohms.
The next step would be to find what is shorted to ground by unsoldering parts one by one. There are just 4 things on that trace that connects the banded end of D3 and the top pin of U5: U5, D3, C2 and C4. Since you have already replaced U5 you probably should start by pulling out the capacitors. For what it is worth, I personally have had a bad C2 right out of the bag from Mouser. The vents on the top were split open and brown electrolyte was coming out. I never applied power to it since I saw it while assembling an O2, so I don't know if it was shorted or not. But it is entirely possible for electrolytic capacitors to be shorted.
So... unsolder those 4 parts one at a time and after each make another resistance reading from that trace connecting to the top pin of U5 to ground and find out which part is shorted. Also be sure to solder that square via hole as I posted above. That could explain how you were able to get +19V on the banded end of D3 while the top pin of U5 was shorted to ground at the same time. Normally you can't have both. But if the via hole were broken it would break the trace.
I'm going to have to bag it for the evening and probably won't be able to log on during the day tomorrow, so the other folks in the forum here can help you further. Good luck!
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Hey agdr,
I removed both C2 and C4 and they were fine. I can't really remove D3 or U5 so I just left them be. They both look brand new and in awesome shape. As do the tracks. The funny thing is, I replaced C2 and C4 again and then I measured the top pin of U5 and I actually got the same reading now as the banded end of D3. But I went to plug it in and I STILL do not get power. I was so confident it would work since I got voltage there at 19 or whatever the D3 had and I figured that was the problem, but now it still doesn't work. This has to be something wrong with the board now right because the parts should work fine?
I removed both C2 and C4 and they were fine. I can't really remove D3 or U5 so I just left them be. They both look brand new and in awesome shape. As do the tracks. The funny thing is, I replaced C2 and C4 again and then I measured the top pin of U5 and I actually got the same reading now as the banded end of D3. But I went to plug it in and I STILL do not get power. I was so confident it would work since I got voltage there at 19 or whatever the D3 had and I figured that was the problem, but now it still doesn't work. This has to be something wrong with the board now right because the parts should work fine?
Actually someone did, back in post #21:
I don't recall you mentioning that you were going back and forth between two different power adaptors. That explains how you measured the correct voltage on D3 at one point.
Glad you got it working! I'm sure you have learned a bit about electronics along the way, too, which is always good.
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jschristian44 - good point! I could see how someone who hasn't worked with all this stuff before would be concerned about that, since the adapter is plugging right into the wall socket.
There is a transformer inside of those, essentially just two coils of wire that are insulated from each other, that separates the wall socket side from the "user" side with the lower voltage. You are always OK touching the "outer" metal part of the output plug barrel. But as for also touching that "inner" terminal on the plug, which would complete the circuit, it is still good to be cautious when measuring the output of adaptors with higher voltages - 20V and above - especially if they output DC (the O2 adapter output AC). Just use the meter probes to touch the inner terminal and keep the fingers away.
Congratulations again on your working O2!
There is a transformer inside of those, essentially just two coils of wire that are insulated from each other, that separates the wall socket side from the "user" side with the lower voltage. You are always OK touching the "outer" metal part of the output plug barrel. But as for also touching that "inner" terminal on the plug, which would complete the circuit, it is still good to be cautious when measuring the output of adaptors with higher voltages - 20V and above - especially if they output DC (the O2 adapter output AC). Just use the meter probes to touch the inner terminal and keep the fingers away.
Congratulations again on your working O2!
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Yup there is still some hope left for me yet. Now that the O2 is working, I can't put it away. It just really is an awesome amp and the best budget amp money can buy for sure. There is no way a sub -$100 amp can beat this thing. Anyways, thanks for all your help. Even though I didn't find the way to my problem through you, you stood by me until I did. Plus I learned how to test components as well and that information is invaluable. I couldn't find anywhere on how to use the Multimeter but now I am pretty confident with it knowing which settings are which. Still haven't used the bottom right of the dial, but I am sure there will be a time. I can't stop building these things. Just completed my second and am ordering 2 more. Thanks again!
Well, since that is one of the first tests in the NwAvGuy's "Initial DIY Testing" instructions, he was told to do that several times on the very first page of this thread.
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