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Originally Posted by: Jordo  Do they have the same p/n's?
I thought I saw different 'Legs' connected to similar components than on the other side so I figured it must be another model OPAMP. Yes, same part numbers, see BOM. Positive and negative half are not exactly mirrored copies (see also OPA209 datasheet, pinout on page 5)
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Update:
First 'Cold Start' of the day went well.
I have my Placid's adjusted to 100mA of Shunt Current and 15,0V +/- 0.1V
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Originally Posted by: Jordo First 'Cold Start' of the day went well. That is encouraging. I will do as you have done and see how it goes.
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Increasing shunt current to 100mA has not fixed the problem. The negative-going side of each board is stuck at -2.5V from a cold start, just like before. Furthermore, I can confidently predict that the output will stay stuck at -2.5V indefinitely. But if I leave it on for a while until it is nicely warmed up, turn it off for a brief moment and turn it on again, the boards will likely perform properly.
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Originally Posted by: avr300 Pls. try copying Miero. Reduce the value of R8B to 150R?
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Yes.
Easiest way to do it is to parallel the 480R with ~150R. This can be done from the "front" this way you don't need to remove the (perhaps) already fitted PSU.
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Reduce it to something smaller, around 100R to 200R.
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Paralleled with 120R resistors. Problem appears to be solved.
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Pls test it a little more to get significance.
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Hi guys, been busy with holiday activities sorry for the late reply. I can't say I have ever seen this symptom occur personally (and I have a few of these running) but I do have an idea what to do to help. First it would be good to know if with the stock resistors when you see in the -2.8V output what is the voltage at the TP_VREF? It should be 2.5V - so one good thing to test would be just reducing R6 (down to even 1-2K would be fine) Reducing R8 is fine too - but we have to be careful not to go too far there as it will load the opamp with current ~ 1.2V over the R (so about 8ma for 150R). I would try something more like 221R (5ma) rather than 150R. Bascially what we are doing when we do that is bootstrapping the opamp. So I would try changing R6 before changing R8. What I think is possible (I can't replicate this so I am not certain) is that the opamp is operating close to it's rail to rail limits on the negative side at start up. Edited by user Monday, December 29, 2014 6:53:58 PM(UTC)
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Hi Russ, Hope you enjoyed your holy-day's :) TP Vref- was approx. 1.65V during the event instead of 2.5V. Best regards, Jordo Edited by user Thursday, November 26, 2015 3:15:39 PM(UTC)
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Originally Posted by: Russ White Hi guys, been busy with holiday activities sorry for the late reply.
I can't say I have ever seen this symptom occur personally (and I have a few of these running) but I do have an idea what to do to help.
First it would be good to know if with the stock resistors when you see in the -2.8V output what is the voltage at the TP_VREF? It should be 2.5V - so one good thing to test would be just reducing R6 (down to even 1-2K would be fine)
Thanks for your reply Russ, hope you've had nice holidays so far :) When the problem occurs (with stock resistor values) TP_VREF- is -1.70V. TP_VREF+ is 2.49V. I will test what happens when reducing R6B. Edit: Jordo beat me to it :) Edited by user Monday, December 29, 2014 7:01:50 PM(UTC)
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Originally Posted by: Stunts Edit: Jordo beat me to it :) Mwoah, I'm just gonna sit and wait. Let you guy's figure it out for me  No but serious. I wait to see if it re-occurs more often. It only happened 1 time to me. I will test it the upcoming day's. If it begins to bother than I will take actions. Jordo @ Russ: Might it maybe have something to do with the grid the system is working on? I remember that the Toslink Lock/ Jitter problem only occurred in 220V country's wasn't it? Edited by user Monday, December 29, 2014 7:10:02 PM(UTC)
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Looking at things closer I suspect R6 *could* help but I must see the effect of one change at a time - it is difficult to debug something I have not been able to reproduce. :) Looking at my schematic I can see where reducing R8 could also definitely be beneficial but I am trying to get at the root. So I must ask one of you to give it a go. :) 221R for R8 is definitely reasonable current for the opamp if it provides good cold startup then we can change the stock value in the kits. Edited by user Monday, December 29, 2014 7:10:37 PM(UTC)
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With the value of the resistors restored to stock value, measurements at turn-on at TP_VREF are as follows:
Board 1:
TP_REF– value is –1.695V
TP_REF+ value is 2.504V
Board 2:
TP_REF– value is –1.694V
TP_REF+ value is 2.499V
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Very helpful thanks. I am really leaning toward simply changing R8 to 221R 5ma loading of the opamp should do the trick. A value from 100-221 *should be* safe - but lower is not really better there. We don't want to excessively load the opamp. Brian and I are a bit stumped - the only thing we can think of is that transistor Vbe differences in some (but not all) cases may enough to need the extra bootstrap current. Edited by user Monday, December 29, 2014 7:27:40 PM(UTC)
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Paralleling the existing R8(470R) with 330-470R should get you close enough to 221R to do the trick. :)
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Okay, only thing is Miero has tried some R8B values a couple of months ago. I'll copy them here: Quote:
R8B:
- default 470R => does not work (2.8V)
- 230R => still does not work (2.8V)
- 220R => works most of the time (it started with 2.8V once)
- 100R => works
So perhaps 221R is still a little too high? It'll probably take more extensive testing to see what works in all cases. Unfortunately I don't have that many resistor values lying around here to do this :( Edited by user Monday, December 29, 2014 7:41:11 PM(UTC)
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Originally Posted by: Stunts Unfortunately I don't have that many resistor values lying around here to do this :( I have but i cant reproducere
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