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Old 14th January 2012, 04:32 PM   #1851
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Originally Posted by agdr View Post
With the batteries removed and O2 power switch off, connect your power adapter and measure the DC voltage from ground (metal shell of the gain switch) to the two outermost battery terminals (closest to board edge and the one farthest from the board edge) and see what you get. Should be around +12V and -12V.

I would take a guess that your power adapter might be mislabeled and may actually be a DC adaptor rather than AC. That would make only one of the two power rails work. Do you have a link to a product page or data sheet for that power adaptor?
It seems like my cheap dmm decided to die too. Guess i'm out of luck. I'll buy a new one asap.
Meanwhile, this is the adapter: Electrónica B.F, S.L. Seems to be correct.
I will report with some measurings as soon as i can.
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Old 14th January 2012, 04:48 PM   #1852
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You could connect 2 LEDs in parallel, with the anode of one to the cathode of the other, and put them in series with a 1k resistor. Connect this to your power adapter set to <24 volts. If both LEDs light, it's AC. If just one LED lights, it's DC.
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Old 14th January 2012, 05:42 PM   #1853
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Hey I like sofaspud's tester idea! That does the job.

raspunsen - looks OK from the picture at least. So post those DC measurements when you can and lets see if your O2 power supply is working properly.
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Old 14th January 2012, 06:41 PM   #1854
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Well, I have -11.91v DC at the battery terminal farthest from the board edge, and 0v DC at the one closest to the board edge. This with AC power only, no batteries installed and power switch off as required.
Maybe a solder bridge? Everything seems ok, but i'll try to get my hands on a magnifying lens to double check.
Meanwhile, i accept suggestions on what may be wrong.
Thanks for the help.
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Old 14th January 2012, 07:41 PM   #1855
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raspunsen - yep, your negative power supply is good but your positive power supply is dead.

Double check the positions of your D1, D3, C2, C4, R1 and regulator U5 match up with the symbols on the PC board, that they are turned the right way. Here is a big close-up picture to compare with from post 1527:

http://img4.imageshack.us/img4/4319/photo4ja.jpg

Hard to see in that photo but both regulators have the metal tab facing the edge of the board. A magnifying glass to look for bridges is a good idea, especially the pins on the regulators. If the positions are OK and no bridges then try re-heating the solder joints on those 6 parts with your iron.

If all that fails, take a voltage reading between ground (gain switch shell) and the cathode lead (with the band, farthest from board edge) of D3. Depends on what your input voltage is, but with 16VAC in you should get somewhere around +24.9Vdc, plus or minus a volt. If that is good then test ground to the anode side (end closest to the regulator) of D1. That should be around +12Vdc. If you get the +24.9Vdc on the first reading but no +12Vdc on the second, then your U5 regulator is bad.

Last edited by agdr; 14th January 2012 at 07:50 PM.
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Old 14th January 2012, 07:58 PM   #1856
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Well, i have R1 turned the other way. I thought that being a resistor, it did not have a correct orientation. All other componetns seem ok.
So, shall i try to reverse the orientation of R1?
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Old 14th January 2012, 08:04 PM   #1857
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No, R1 has no orientation.
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Old 14th January 2012, 08:27 PM   #1858
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Quote:
Originally Posted by agdr View Post
If all that fails, take a voltage reading between ground (gain switch shell) and the cathode lead (with the band, farthest from board edge) of D3. Depends on what your input voltage is, but with 16VAC in you should get somewhere around +24.9Vdc, plus or minus a volt. If that is good then test ground to the anode side (end closest to the regulator) of D1. That should be around +12Vdc. If you get the +24.9Vdc on the first reading but no +12Vdc on the second, then your U5 regulator is bad.
The reading on the cathode lead of D3 is kind of tricky. If i put the tip of the DMM in the square on the board it reads 24.7 volt, but if i only touch the "leg" it reads around 8 volt.
If i understood the reading on D1, with the black tip of the dmm on the ground as before and the red tip on the anode side of D1, i get 0.00volt.
So, maybe U5 is dead. I'll try to heat the solder there, but i have my hopes quite low...
Thanks again for all the help.
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Old 14th January 2012, 09:55 PM   #1859
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raspunsen - the board square on cathode D3 is what counts. +24.7Vdc there is OK. It does sound like your U5 is bad. One other thing to look for is a broken or damaged PC board trace between D3 and the regulator, or between the regulator and D1. I've actually heard of this happening to one person. They didn't have wire cutters so were bending the wire leads back and forth to cut them and damaged the board traces. Unless you have done somethng like that, or had a tool slip and cut a trace, your U5 is most likely bad.

Here is a tip on getting U5 out. Take some copper de-solder braid and put it across all 3 regulator pins on the bottom of the board. Then lay the soldering iron tip flat against the braid and heat the braid. It will spread heat to all 3 leads at once and the regulator just drops out via gravity.
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Old 14th January 2012, 10:42 PM   #1860
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I packed it all up for today but i'll have a better look tomorrow (I'm in GMT timezone).
I have used a cutter to trim the leads, so it's probably U5 that is gone. Maybe i gave it too much heat while soldering...

Guess i will keep using the O2 on batteries only until i find a cutted trace or a replacement regulator. I bought everything from Mouser, so i just hope my local electronics store have some of the same kind.

As for the dessoldering, i have a dessoldering pump to help me, i guess i'll be ok.

Again, a massive thank you for all the help.
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