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The + rail works fine. The - rail does not respond to setting via VR3.
I have checked out that VR3 is working and all is OK. The is current through the transistors, all LED are alight. I think the opamp may be dead. Any ideas???
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The first think to check would be the transistors are in the correct positions, and the correct parts. What voltage does the negative rail sit at, and at what input voltage? How does VR1 behave? Edited by user Tuesday, November 16, 2010 2:52:25 PM(UTC)
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Rank: Advanced Member
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VR1 adjusts the bias current correctly, adjusting it changes the voltage across R1. I have double and triple checked the positions of the transistors and resistors. I have double checked with the other Placid that is working as the parts list on the site appears to be out of date.
The output voltage of the - rail is not stable it drifts up towards 0V after power on. Adjusting VR3 makes no difference.
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The LEDs are light correctly? Any chance you could attach some pictures?
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As mentioned in my first post all LED are alight. VR1 adjusts the bias current (voltage across R1) just fine. The heatsink warms up. The output voltage is not stable, it drifts towards 0V at aprox 100mV every 2-3 secs.
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Rank: Advanced Member
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Still no joy with attachments so I have emailed them. I have been over the board with a fine tooth comb and my multimeter. Every joint has continuity. Just to be double sure I reworked a couple of the ground plane pads that did not look 100%. The ground plane pads are rather small and the heat sink from all that copper can make it difficult to get a nice clean job. steveww attached the following image(s):  placid.jpg (252kb) downloaded 53 time(s). transistor.jpg (155kb) downloaded 56 time(s).You cannot view/download attachments. Try to login or register.
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