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Hi Hope someone can help me out with this one! I've wired up my placid, adjusted VR1 and VR2 as per manual and fired it up: LEDs are on, no smoke but adjusting VR2 has no impact on the output, worse still the output is only c.1V rather than c. 4V I would expect. I've double checked the board and made sure I didn't accidentally switch the transistors and... have reached the limit of my electronics knowledge. Any pointers (aside from my soldering sucks)? Thanks, Mark Voltages: Input AC: 10.4V, output is c. 1V IC: Pin 6: 11V, Pin 3: 3.2V [Edit: Pin 7 was 11V not 6!] QP1: Pin 2: 1v, Pin 1: 10V Transistors: QP2: BC560C QN1: J5200 QP1: J1943 Q2: PN4393 Edited by user Tuesday, January 3, 2012 8:50:32 AM(UTC)
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I'd start by resoldering R3, R4 and R5.
Also, is the VR1 / VR2 resistance in line with what you would expect from them?
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Hi Leon, Thanks for the reply. LeonvB wrote:I'd start by resoldering R3, R4 and R5.
Also, is the VR1 / VR2 resistance in line with what you would expect from them? VR1/VR2 are initially set to about 100 Ohm/ 10k Ohm respectively. The joints are R3, R4 and R5 seem ok to me even though the solder hasn't flowed through to the top side of the pad, or are you referring to something else? Thanks, Mark
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Double double check that you have not swapped transistors. :) Also look carefully at the opamp. Edited by user Monday, September 19, 2011 5:29:27 AM(UTC)
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Big delay - back onto project....
Hi Russ,
Thanks for the reply. I have n-tuple checked the transistors. Only diff I can see with the datasheet is QP2 is BC560C not BC560B.
The opamp has the dot in the right corner... voltages:
(4,7 0v and 11.6 v respectively)
2: 2.5v
3: 3.2v
6: 0v
Vref is ok at 4.3v, but the output is stuck at 1ish and QP1 is all toasty.
Anything else obvious before I tear it apart?
Thanks,
Mark
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Update and close - I replaced QP2 and Q2. Board is working.
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