Reusing power supply from a printer - please help.

Hi everybody. Spent two days (literally) trying to reuse a power supply from a printer with no success. I took apart two large printers and have the same issue: 3.3v, 5v and 12V work fine but 24v does not output any current. It requires some kind of feedback or input of lower voltage (just like ATX power supply) but cannot figure out how. Tried just about any kind of loop-back with “flowing” or “static” current to no avail. At this point, it is not worth from the time perspective but it has become a challenge. I have attached pictures of the board itself and setup I was running trying to “fool” it into turning on the supply. I am relatively new to electronics and arduino and the goal is to build arduino powered CNC. Please help.

At this point I am not trying to “fool” the PSU to output the 24V but rather trying to figure out the PCB and modify it so that the output happens without any kind of feedback (is there a relay that is controlling the output?). This would also allow not to have a 5v supply running on a side all the time. The first picture is the entire set-up when trying to hack it. The rest of the pictures are the closeups of the PSU’s PCB. thank you again.

Some more pics of the board.

Hi, you say that you have 24Vdc output but when you try to draw current, what happens, how much volt drop.

Check the 2200uF 35V capacitor, if it has gone low in value, or high in ESR then it will not provide the necessary output filtering and cause some voltage feedback errors, in fact check all the electolytic capacitors. Caution around the 400Vdc capacitor, make sure they are discharged before touching them.

Tom...... :)

Hi, It does not put out any current at this point. the manual says that there is a need for 5v input (which I did) and plus several closed door feedback loops that go through a motor controller - otherwise the PSU will not work. these are the three small yellow wires on the first picture that go into the four prong plug (5v being the fourth). I just cannot figure out what the feedback loop should look like. there is another small yellow wire coming out from the 5v PSU and it puts out -2v; i tried this as an input with no success.