Hello everyone,
I bought an old Olivetti M300-30 486 PC, which obviously has a non-working power supply.
I should point out that I know how dangerous it is to handle a switching power supply due to voltages in games, so I will take all the necessary precautions.
The problem encountered in the power supply is that it turns on for a few seconds and then turns off, obviously even when not connected to the PC.
I have already removed various components from the board, electrolytic capacitors, transistors, mosfets, voltage regulators and diode bridge. For the zener diodes and resistors I only removed one pin to check them with the tester. From the measurements made with the multimeter, all the resistors are ok, as well as the diodes/zener. The capacitors all have a very low ESR value. Diode bridge ok. The 7805A, if I try to power it on the input I only get 1 V on the output (so I will replace it). The two IRF830 mosfets are ok, tested with a T7 multifunction tester. The S30SC4M Schottky diode is ok. The FEP16BT diode is ok. The CNX83A optocoupler that I tested with the multimeter recognizes it as an emitter diode and NPN receiving transistor. The TYN112 with the tester sees it as a resistance, so in my opinion it should be replaced. Finally, an integrated circuit that I believe controls the PWM signals, but I can't figure out what it is, has a "Δ" 0177 U printed, but I haven't found anything on the internet. So I ask you what could be the cause of the failure of this power supply, in light of the components already tested? What type of integrated circuit is the "Δ" 0177 U and how can I test it? Any advice is welcome. Thanks