Read Harman Kardon ONYX STUDIO 2 (serv.man2) Service Manual online
3.5. TP702/ TP700 (+4.7V)
1. Connect good DC board/ USB board and KB to MB.
2. Set power supply 3.8V, connect to MB J700
3. Set another power supply to 19V/ 2A and plug in DC jack
4. Monitor power supply 19V/ 2A voltage if it drop to very low (close to 0V), it must short in somewhere;
else go to next step
5. L701 is defective if TP702 voltage is not close to 18.7V
6. Check U700 pin3 voltage is close to 3.3v or not, if not R703 or R705 is defect
7. It must be something wrong in the U700 circuit
Click on the first or last page to see other ONYX STUDIO 2 (serv.man2) service manuals if exist.