Power Supplies Problem

[muashr]

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!!!

 

[duke37]

I assume these are two seperate power supplies.

The first one could have a fuse blown or a bad connection somewhere.
The second may have a faulty potentiometer.

You will need to get an idea of the type of supply to narrow the fault down and maybe draw your own circuit diagram.

Some pictures of the supplies would help. Are they based on semiconductors or valves (tubes)?

What is the input power source?
What should the output voltage range be?

 

[muashr]

I assume these are two seperate power supplies.

The first one could have a fuse blown or a bad connection somewhere.
The second may have a faulty potentiometer.

You will need to get an idea of the type of supply to narrow the fault down and maybe draw your own circuit diagram.

Some pictures of the supplies would help. Are they based on semiconductors or valves (tubes)?

What is the input power source?
What should the output voltage range be?

Thanks for the reply.
Yes, these are two different supplies.
The input is common (220-240)V 50/60 Hz.
The dc output voltage range is from (0-20)V.
These are semiconductor based.

 

[shrtrnd]

You didn't mention the make or model of your power supplies.
Some of the high-end power supplies have output voltage terminals that have a 'current sense' set of terminals. If the current sense is not hooked, up, the output voltage is abnormally low.
Like I said, it's difficult to give anything other than generic guesses without more specific information about what you have.