OK - I have built 2 LCDPS, a Placid BP PS and a Placid PS. All work just dandy.

Note: All of the following voltage measurements made with the Placid powered without load.

Problem is a second Placid does not. VR1 set to 100 ohms andVR2 set to 9.7K. There was no smoke (or other fireworks) on initial power up. The LEDs light up. With 10.95V AC in, I can measure appropriate voltage across C1 =13.83. Voltage across C5 = 4.07. However, voltage output is fixed at 3.3V to 3.5V regardless of adjusting VR2. VR2 resistance does change with adjustment. I would also mention the neither heat sink gets warm. Now in case you are wondering about the transistors: Q2 = PN4393, QP1 = FJPF1943, QP2 = BC560 and QN1 = FJPF5200.

Voltage Measurements:

QP1(FJPF1943): B = 13.08, C = 13.71, E = 13.71
QN1(FJPF5200): B = 0.0, C = 3.475, E = 0.0
QP2(BC560): B = 12.77, C = 0.0, E = 3.42
Q2(PN4393): G = 4.25, S = 4.55, D = 13.04

IC1:

Pin 2 (-In) = 3.38
Pin 3 (+In) = 4.08
Pin 6 (Out) = 12.77


I referred to the Fairchild datasheets for each device for semiconductor pin orientation.

Any ideas as to what is actually wrong?

My guess is that QP2 is defective (and it is only a guess).

Edited by user Sunday, July 3, 2011 8:52:40 PM(UTC)  | Reason: Not specified

OK gang the problem is solved.

It appears that ALL semiconductors were installed correctly.

I might add that BC560C is a pin for pin direct replacement for BC560B.

The output terminal block pins were a very tight fit going through the PCB holes and solder did not flow through the + output hole to the trace on the top of the PCB which goes to the collector of QP2. The trace from the collector of QN1 on the bottom of the PCB was soldered OK. This was in spite of a disgusting amount of flux applied to all points on the bottom of the PCB for reheating. I might add the clean up after the flux job was even more disgusting.

The solution was to heat up the output terminal block pin on the bottom of the PCB and sneak some solder to the + output pin in the exposed area just under the metal part of the terminal block on the top side of the PCB.

The Placid now works!

This was a tough one to find. The terminal block on the top of the PCB obscured the view of an essentially unsoldered joint. This is something to keep in mind if you encounter problems with a build.