Well, it seems that I found the problem. The previous owner probably did a modification: I found that a PCB trace that is going from the "Voltage" potentiometer is cut! There are 3 wires that soldered to the PCB contacts of the "Voltage" and "Fine" pots to the rear of the unit to the round DIN5 connector. I think the user did this mod in order to use an external potentiometer to control the voltage. The previous and the current users utilized this unit as a voltage source for the microscope lamp (in the research labs). However, the current user do not use any external potentiometer, so the unit was actually working but only the "Current" potentiometer was functional and was used for brightness control. It seems that in this mode one of the 100 Ohm resistors and one zener (5.1V) overheated, and finally damaged. After replacing the resistor, zener (I used 5.6V) and repairing the PCB trace that was cut, the unit works, both current and voltage are adjustable. The resistor and zener do not overheat anymore. I think the voltage reading of the display have some fluctuations when the load (24V 6Watt lamp) is connected to the output, should it be so? The 3000 series could produce up to 30V and up to 10A, so with the above load at 24-25V I am getting about 0.25-0.3A and the "Current" is fully cranked to the maximum. Theoretically, you cannot get more current (6W/24V = 0.25A; the resistance of the load is pretty high - 24V/0.25A = 96 Ohm), the voltage is nearly maximal. When the outputs are shorted, I can get about 10A at 30V. So, do you think these readings are normal?