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Old 30th September 2012, 11:01 PM   #2831
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Hi all, I need help. Not unexpectedly, but still frustratingly, I am having problems putting together my O2. To summarize the situation:

I populated the board, saving mosfets for last. Had an ESD mat that connected to a ground at outlet and my body via wrist strap. My soldering iron (Metcal SP200) is supposed to be ESD safe and is plugged into an isobar in a lab.

My R5 resistor (270kohm) read funny ~150k or ~80k depending on how I used the leads on my DMM. I left it and went ahead with power testing. Everything was within normal ranges until I got to U2 Pin 2, which read high near 9v. The other pins were ok except Pin 7, which was a negative 8v. According to the troubleshooting guide, either my U2 or my Q2 or my R5 are wrong or broken.

After a week of waiting I got replacements for all 3. First I swapped the U2 since that was in a socket. Same measurements as before. I then swapped the R5 resistor. Got better readings ~120k for resistance, but U2 pins all had same problem. I then replaced the Q2 mosfet, being as careful as possible with handling. Still roughly the same measurements.

I am stumped. I checked for solder bridges, reflowed nearly every connection, re-tested several times. Anyone know what I can check next? Maybe I am still doing something wrong with mosfet handling despite all my precautions. I have one more spare mosfet in case that is still the problem.

Thank in advance.
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Old 30th September 2012, 11:15 PM   #2832
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Anybody know what's become of RocketScientist? He hasn't posted here since July and the last entry on is blog was back in May.

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Old 2nd October 2012, 03:46 AM   #2833
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Hello.

I have a slight problem with my O2.
After few hours of running on batteries, the amplifier does not come back to life after switching it off. Plugging in AC power for a brief moment while the switch is on lets it come back to life and work much longer.
This issue does not seem to occure when batteries are fully charged.
Could it be that MOSFETS suffered from ESD and "get stuck" ?
I tried testing them with almost depleted batteries and the result was rapid on/off cycling.
Maybe using the old values for R9 and R25 would resolve my issue?

Best regards.

Edit: I suspect that my batteries are 6 cell.

Last edited by HurlockVanguard; 2nd October 2012 at 03:58 AM.
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Old 2nd October 2012, 06:33 AM   #2834
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HV, you could try new resistor values. It may help. Personally it's difficult for me to see your problem.

fraggler, your O2 malfunction is tougher. Your going to have to pause, take a deep breath, and attack it again. Inspect and inspect again. Think about it and think about it some more. Measure and measure again. In other words, the opposite of your R5 troubleshooting.

TWIMC, I have no ESD mat on my bench, and haven't used a wrist strap or my ESD-safe soldering iron in quite a while. I was, though, able to solder my O2 FETs with no problem. By just halfway understanding the ESD failure mechanism and avoiding it. That's more important than anything you can find in a catalog, IMO.

PS Yeah, this was sort of a "tuff luv" post. Don't be offended please.
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Old 2nd October 2012, 07:41 AM   #2835
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Thanks for your reply.
I am using new resistors values already.
I will test it with a power supply tommorow so I can try and replicate the issue.
Maybe I am letting batteries overdischarge by doing this.
Sadly right now I have no access to a DMM so it will have to wait.
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Old 2nd October 2012, 04:06 PM   #2836
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Sofaspud, tough love is fine

I am learning about the circuits concurrently with building. Unfortunately, it is self taught from scattered resources that I have found online (even the wikis here are incomplete). I tried working down the power chain testing each piece to see if they were measuring properly in the circuit (everything measured fine out of the circuit), trying to find where the break point was. I guess what I was looking for was help with the next level of knowledge, as I know what everything does, but not how or well enough to know what might actually be wrong. I also learn better through discussion.

If you can't help with the actual troubleshooting, do you know of any guides that might help me learn enough to troubleshoot it myself?

Quote:
Originally Posted by sofaspud View Post
HV, you could try new resistor values. It may help. Personally it's difficult for me to see your problem.

fraggler, your O2 malfunction is tougher. Your going to have to pause, take a deep breath, and attack it again. Inspect and inspect again. Think about it and think about it some more. Measure and measure again. In other words, the opposite of your R5 troubleshooting.

TWIMC, I have no ESD mat on my bench, and haven't used a wrist strap or my ESD-safe soldering iron in quite a while. I was, though, able to solder my O2 FETs with no problem. By just halfway understanding the ESD failure mechanism and avoiding it. That's more important than anything you can find in a catalog, IMO.

PS Yeah, this was sort of a "tuff luv" post. Don't be offended please.
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Old 2nd October 2012, 10:41 PM   #2837
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The problem appears to be confined to U2. Not the simplest of comparator circuits. You measured 9V on pin 2, when it should be approx -9V. Pin 7 measured -8V, when it should be closer to +8V. Basically "upside down." Measure all the U2 pins and post the results so we can see just what all the inputs and outputs are.
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Old 4th October 2012, 04:17 AM   #2838
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Quote:
Originally Posted by sofaspud View Post
The problem appears to be confined to U2. Not the simplest of comparator circuits. You measured 9V on pin 2, when it should be approx -9V. Pin 7 measured -8V, when it should be closer to +8V. Basically "upside down." Measure all the U2 pins and post the results so we can see just what all the inputs and outputs are.
Or check the leads on your DMM. I know that sounds funny, but you never know.
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Old 4th October 2012, 08:29 AM   #2839
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Any progress? Just trying to keep the discussion moving here until you're enjoying listening to your O2.
I don't want to hijack this thread with general troubleshooting philosophy. That could be given it's own worthwhile thread if you'd like. Sort of a supplement to the Recommended books thread.
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Old 7th October 2012, 08:41 PM   #2840
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A combination of work, travel, and illness have prevented me from getting back to the O2 since I asked for help. Hopefully this week. I do appreciate you following up.
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