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Yes you're right. Which leads me to think something isn't proper connected.
Remember you're are measuring in-circuit. The good thing is, that you have a working side for reference. So the measured 1k2 is ok.
The measured 2k is almost as it's not connected. That's why I recommend re flowing around the trouble zone.
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Allright, One thing has changed; Both R6A and B show around 1100+ Ohm. Ref 2A- 2 Shows 1.00V instead of 0.6 before the points were reflown. R13A still 2.49--> 3.34V R6A 2.49 --> 20.3V Still the pots aren't adjustable... How can it be that in front of R13A the voltage is 2,49 volt, and after the resistor it is increased to 3,34 V?? Indeed at R13B the voltage is 2,49V at both sides.... Edited by user Saturday, December 27, 2014 5:09:35 PM(UTC)
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1.00 and 2.5v on the same wire gives makes no sense.
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You're right, The middle one of REF2A shows 2,5V One outer leg is GND and the other outer shows approx. 1V. Edited by user Saturday, December 27, 2014 5:28:24 PM(UTC)
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Don't mix in the 3 and unconnected leg of REF2.
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Yes I did... Jordo attached the following image(s): cut2r1.jpg (66kb) downloaded 2 time(s).You cannot view/download attachments. Try to login or register.
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It still "sounds" like a bad solder joint.
Try shorting R13.
R13 | C8 is a filter introduced for filtering any noise coming from REF. The circuit can and will work without it.
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We need 2.5v @ +input of the opamp.
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Yes we do! I've placed a jumper like this. Only over the terminals of R13. Agree? Jordo attached the following image(s): Jump R13s.jpg (231kb) downloaded 1 time(s).You cannot view/download attachments. Try to login or register.
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Ok, we have 2,5V at both sides of R13A now. IC1 receives 2,5V. VR2A receives 3.16 iso 4.0V But the reference side receives 2.5V at the Potmeter.... R8A 20.7V iso 21.1V IC1 Pin 2 gives 3.16V to VR2A.... Edited by user Saturday, December 27, 2014 6:47:25 PM(UTC)
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can you change the 3.16v by turning the pot ?
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Can you trim down the output to ie. 14v ?
Also check that you're shunting some current, min. 50mA.
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I can turn the Shunt Current up but I cannot get it below approx. 60mA. I can influence the Voltage to VR2A by turning the pot. I cannot influence the TP_OUT+. That one is stuck at approx. 20,7V... Do you mean that I have to turn the voltage to VR2A from 3.20v up to 14V? When turning VR2A over a larger range I can make small variations to the output from approx. 20.5 to 21.5 V that's all.. Edited by user Saturday, December 27, 2014 7:25:49 PM(UTC)
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No. Try to adjust down the VR2 voltage to around 2.5v (compare numbers/symmetry with the good side).
Does this change the 21.1v (output of the OMAMP)?
If yes, does this change the output voltage ?
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Ok to begin,
- I reflown all solder joints from the A side.
- I adjusted VR2A to 2.5V
- IC1-3 get's it's 2.5V
- TP_out + shows 14.25V
I am able to adjust the voltage within a certain range but the strange thing is that the Voltage is very depending on the current. Even with 60mA of Shunt Current I'm not able to increase the Voltage to a maximum and that is strange.... When increasing the Shunt Current the voltage can be adjusted again.
But for now,
Output is set to approx. 14V.
VR2 is set to 2.5V
If the resistance of VR2 is adjusted:
- It does change the output voltage
- It does change the output of the OMAMP
- it does change the voltage to VR2. (Voltage to VR2 = Voltage IC1-3)
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The I have to ask - what's missing?
To me it sounds like the PSU is running ok (now) ?
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It still behaves a bit strange in my opinion. Normally when the voltage is set it should not respond to current increments isn't it? But I think I can hook it up with the IVY now. See what it does. What voltage is recommended for these PSU's? Do they also drift? And can I remove the jumper? Edit 1: When VR2 is set to 2.5V by adjusting VR2, Output voltage can only be set by adjusting VR1 Edit 2: On 2nd thoughts, I'm not gonna hook up the IVY like this. Before you know it the voltage shoots to more than 20V... Edited by user Sunday, December 28, 2014 11:46:44 AM(UTC)
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I think the fault must be located in the VR1 circuit.
When I completely lower the Output Voltage and Shunt Current near zero I can turn the voltage up until it lacks current.
Then you turn the current up and you can continue to adjust the voltage. So far so good. Up to about 14.5V.
When the output is not increasing anymore after 14.5V, you turn up the current again.
Now suddenly the Output voltage shoots to 20.5V and it isn't adjustable anymore by VR2.
Somewhere between 95-105 Ohm of VR1 the output voltage jumps and becomes uncontrollable.
My guess is that we have a failure within a component that causes a short at a certain threshold.
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And that is exactly what it was!!!!! I took a real close look at the Voltage Regulators with a magnifier and spotted a really tiny Tin Bridge between the Legs of QP4. After removal all works a advertised!!!  Thank you so much AVR300 for all your patience, time and help!!
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