7651 Programmable DC Source inaccurate voltage

[deJong]

Hello Electronic Enthusiasts!

My old DC source giving me troubles. Used to be very accurate in producing output voltages for Sense (Hi and Low) and Out (Hi and Low).
Here are the pictures. The source is programmable, and outputs and are exact anymore. The lower voltage you want, the higher you see the difference from Out and Sense.






I tried to troubleshoot and find the problem but I think my knowledge in this is not good enough. Please help...

 

[chuckey]

Normally the sense and the out put terminals are connected internally with a 100* ohm resistor.This is so for low currents, no sense wire connection need be used as the volt drop down the wires would be very low.
If someone connected the external kit to the sense terminal without a good connection to the main output, this 100* ohm resistor can get overloaded. if its , say 1M ohm, the current taken by the sense amplifier will cause an increased volt drop across this resistor, so the amplifier cranks up the main output voltage to compensate.
* Other values are available
Frank

 

[deJong]

is this what you are talking about?


I checked and traced back the output and found this relays directly connected to its output. I also measured the one you mentioned, Out and Sense high reads open while Out and Sense low reads around 34Mohms. Please check this block diagram. I don't have the schematic.

 

[chuckey]

The diagrams are not correct. if you look at the first one, showing links between the output terminals and the sense line. If that link was open circuited, the voltage sense would say low output and wind up the output voltage to maximum. Which is clearly dangerous to external electronics. So that link is shunted by my "100" ohms resistors permanently.
Frank

 

[deJong]

So which one is bad? Out and Sense High reads open or Out and Sense Low reads around 39Mohms?