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Old 3rd January 2013, 08:06 AM   #2981
kuished is offline kuished  Singapore
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My transformer works. I have a working O2 (a friend built it for me) which I use it with. Output is 15V ~500mA
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Old 3rd January 2013, 08:39 AM   #2982
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Quote:
Across D3 is 26.7V, across D4 is 26.1V.
Whoa. These should each measure about 0.7 volts across.
I think you are measuring wrongly.
Have you done the inspection? Are the components oriented correctly? This has bitten more than one O2 builder.
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Old 3rd January 2013, 08:56 AM   #2983
kuished is offline kuished  Singapore
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Yes I am very sure that the components are oriented correctly. A visual inspection also reveals not much wrong with the soldering. I measured the voltage across by placing the probes on either side of the diode leads. (or maybe I am doing something massively stupid and this is not the way to measure the voltage across)
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Old 3rd January 2013, 09:01 AM   #2984
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Maybe the diodes are both open.
Or maybe Kirchoff is rolling.
I'm afraid I have to give up. Sorry.
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Old 3rd January 2013, 09:17 AM   #2985
kuished is offline kuished  Singapore
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As a last measure, I measured the same components in a verified working O2, it measured 25V for both D3 and D4.

So our measurement techniques must be different.
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Old 4th January 2013, 04:54 PM   #2986
ericj is online now ericj  United States
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Default So what did i do to break it?

My self-built O2 was working quite well. I am an experienced circuit builder so this came as no surprise to me.

And then i took it on a trip. And the wall transformer i brought with me turned out to be 12vdc, and i didn't realize that mistake until I'd tried to charge and/or power the O2 with it for some hours.

I finally laid hands on my 16vac transformer again today and the O2 is silent.

I haven't got the right screwdriver with me right now at work to open it up.

When i get it home and have the ability to open it up and prod at it with diagnostic implements, what should i look for?
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Old 4th January 2013, 06:28 PM   #2987
agdr is offline agdr  United States
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Quote:
Originally Posted by ericj View Post
When i get it home and have the ability to open it up and prod at it with diagnostic implements, what should i look for?
I'll take a guess that the negative voltage regulator (U6) is dead if your DC supply was tip-positive and that U5 is dead if your adapter was tip-negative.

The reason is that RocketScientist probably should have included reverse-biased rail-to-ground 1N4003 diodes on each rail. I've been meaning to post that in the modification thread for awhile. The diodes would clamp any static voltage on the opposing rail to 0.7V in the event the supply (or battery) on one rail suddenly disappears, which is what happened with your DC supply. If your DC adapter was tip-positive, then it would have forward biased D3 and lit the positive rail with the negative rail left floating by the reversed biased D4. The positive regulator would have gone into dropout, with only 12Vdc into a 12Vdc regulator, but would have passed what it could on to the positive rail, probably in the +8Vdc to +11Vdc range.

The trouble comes when rail-to-rail parts like the U2 op amp, R5/R9 voltage divider, and D7 power LED, leak positive voltage onto the (now floating) negative rail, forming a static (very low current capability) positive voltage on the negative rail that otherwise was left floating by D4 being off. RocketScientist did a very good job keeping the current draw of the parts before the mosfets low to reduce battery drain (the mosfets would be off with only one rail lit), meaning there is not much rail-to-rail bleed resistance, allowing that static voltage on the opposing rail to remain fairly high. I would guess maybe +8Vdc-or-so on the negative rail.

And that would put a reverse voltage on the negative voltage regulator. Its output pin would be at +8Vdc with respect to ground (initial conditions of the uncharged C3 and C5 left floating), which would pretty much kill the regulator instantly. They don't like being reverse-biased, even for an instant. If a reverse biased diode had been in place between ground and the negative rail it would have clamped the static reverse voltage across U6 to -0.7Vdc, which would have greatly upped the odds that it would have survived.

You can confirm the diagnosis here if you have a DMM by powering up your O2 with the correct AC adapter, then measuring the voltage from ground (metal shell of gain switch) to D1 anode for positive reg out and D5 cathode for negative reg out. One reg is probably working and the other isn't (if U6 is dead you will see a positive voltage on both D1 anode and D5 cathode, or vise versa if U5 is dead).

Last edited by agdr; 4th January 2013 at 06:42 PM.
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Old 4th January 2013, 08:14 PM   #2988
ericj is online now ericj  United States
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Thanks. I'll debug this weekend.
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Old 5th January 2013, 03:00 AM   #2989
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Default Where to buy O2 PCB's?

I just recently found this thread, and became aware of this project. It's weird- thousands of posts, dozens of webpages, and I can't figure out where to buy a PCB for the O2. The BOM that is posted on NwAvGuy's website says the board is TBD. I'm guessing there's a more current place to find it. So, can someone tell me my options for purchasing a current version PCB for the O2 (USA)? Or where to find that info? Thanks, Keith Ostertag
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Old 5th January 2013, 03:18 AM   #2990
Davey is offline Davey  United States
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JDS Labs - Objective2 Printed Circuit Board / O2 PCB

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