I recently got a broken power supply from college, a univolt DT305DD dual 30-3.And i am looking for some help because of that lack of it and i don't know much about the frequent failure in these type of linear power supplies.
I am looking for possible service manuals(if there is any, i can't see if they have a website)
Type of failure:
-Output 1 wrong voltage min-max(0.7V up to 6V)
-Output 2 wrong voltages also but difference voltages(min:3.3V max 32V(fine the max)
-At the last moments of the testing time i made both outputs had a output voltage of +-52V even with turning the output 2 knob and being in "indep" mode(i got scared with those voltages because the main cap is rated 50V and the output one was larger and both outputs had that voltage)
Type of power supply:Op-amp linear
Meters than i have available:
-UNI-T UT50A 2k count multimeter volt, 20 amps, ohms
-Fluke 8060A 20k count multimeter volt, 2 amps, ohms
-Fluke 97 60Mhz 3k count scopemeter volt, scope, ohms
Thinks than were checked:
-Fuse housing(replaced because it was stolen(go figure)
-Current and voltage control pots(all 4),they are 6.8k but read 3.8-4k max
-Any visual damage in caps(they are DH caps so seem bad and the main 4700uF 50V are vent-less)
-Construction of the unit
-Output voltages and meter accuracy(fluke 8060A used)
-Output transistors
Components replaced for now:
-Fuse housing and placed a 2A ceramic fuse(the recommended one is 4A but that is too high for my taste, the fuse is on 230V phase)
-The meters power supply(KA7805 based) has now terminal blocks for easy removal(also planing to supply those meters with 2 mc34063s)
Thinks than i am interested in knowing:
-Is it right to replace the pots with 4.7k ones or is it better 10k ones?
-What can cause the wrong voltages?(i don't know about op-amp still but i think than it is time to get ahead my class again)
Pics:
Power board(equal for both outputs,this board is for the output 2)