| Electronics > Repair |
| ASTEC AA16242 Power Supply for Olivetti 486 PC 90's |
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| fabry891:
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 |
| m k:
Few pictures wouldn't do any harm. It doesn't work properly without a load. Transformer and 6 pin opto between heatsink and fan are above the segregation line. Opto is giving feedback to 8 pin switcher chip. To test it you must turn it on. Without a load the switcher must still start. |
| Swake:
There is some info out there. Found this picture. Unfortunately too low resolution to be of much help. For some reason the delta 0177 U sign is familiar to me, but I can't pinpoint it yet. |
| fabry891:
I have a second power supply that works and turns on even without a load. However, if I try to connect it to the PC, the various power supplies are ok, but the PC does not start, and the power supply "restarts" continuously, as soon as I have time I will try to measure the optocoupler. Thanks |
| pienari:
Is there a short in mainboard? |
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