Voltage adjustment on 12VFB

[wegrei]

Hi there, thanks for your good explanation. I am planning to build an adjustable battery charger. Try to conttroll output voltage and respectively current by using your method. However I have a problem. Have connected a 12k resistor with a 5k potentiometer in series, the other side of the 20k resistor goes to 12VSB (pin37), the other side of the potentiometer goes to GND (pin 1-14; 39-51) on the board. The wiper goes to 12VFB on the main board as described. With this setup I can adjust the 12VFB from 0v - 2,7V. From 2,7V down to approx. 1,7V the output Voltage stays constant, below that value the unit shuts down. Do you have any idea what is wrong? The model I have is a DPS-1200FB A / HSTNS-PD11 / P/N438202-002
Can you help?
Thanks a lot in advance
Werner