Reply To: Super hot U5 and no leds ON on OSSC 1.6

[Morpheus_79]

The OSSC should work without D5… but removing D5 and shorting the fuse isn’t a good idea, because:

D5 is TVS diode that clamps voltage to 5V (in reality effective clamping voltage is a bit higher and depends on current), protecting from surges and overvoltage. When continuous overvoltage (or negative voltage with more than ~0.6V amplitude) is applied, it burns into a short circuit so that downstream devices are still protected. That eventually triggers overcurrent protection (e.g. fuse) if such is present. The diode and fuse are placed before power switch, so if you hadn’t power turned on yet, then you almost certainly did not damage anything but the diode.

If one or both are broken, than it’s  for a reason. Circumventing both may damage your OSSC further.

If U5 gets very hot, you should check for shorts like described here:

https://github.com/marqs85/ossc_pcb/blob/v1.6/assembly/assembly_tips.txt

It’s a good idea to check that power supply lines are not shorted to ground. It can be done easiest by checking all the regulators:
-on bottom side, there are 8 small regulators in SOT-23-5 packages (U6, U7 etc.). Verify with a continuity meter that only the middle pin on the side with 3 legs is connected to ground
-on top side, there is one larger regulator (U5) behind the display. Verify that only the middle pin (on the side with 3 pins) and the heatsink pin are connected to GND