Problematic Power Supplies

Hi,

Two power supplies are malfunctioning. Both have problems with their variable DC output voltages. The DC output voltages can be varied using a potentiometer.

The first supply gives a fixed negative output (which is much lower than the maximum +ve output obtainable) for all possible values (That is the values which can be got using the potentiometer).

The second supply gives higher output than it should be as the shaft of potentiometer is rotated and reaches the maximum value before the shaft of the potentiometer got completely rotated after that if the shaft is further rotated the output starts to increase from the start again.

Can anyone make any educated guesses about the potential causes/problems? Or give any suggestions?

No circuit diagrams available!!!

No circuit diagrams available!

Click to expand...

Then not much chance of a solution

Are they connected to a common point?

Are they being tested separately? With / without load?

muashr said:

No circuit diagrams available!!!

Click to expand...

Then draw it out!!.

Chip part numbers?

atferrari said:

Are they connected to a common point?

Are they being tested separately? With / without load?

Click to expand...

These are two separate variable dc power supplies. The type and manufacturer is the same. They worked previously ok but right now they have problems.
One gives a fixed -ve voltage instead of variable dc voltage and other one gives voltage higher than expected as the shaft of the potentiometer is rotated.

Have you managed to draw a circuit diagram of either supply for us to see?

Have looked for the control chip part numbers?