ASTEC AA16242 Power Supply for Olivetti 486 PC 90's - Page 1
Forum section: electronics / repair

author: fabry891
author_rank: Newbie
timestamp: December 26, 2024, 05:19:50 pm
content: 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

author: m k
author_rank: Super Contributor
timestamp: January 04, 2025, 09:34:33 pm
content: 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.

author: Swake
author_rank: Frequent Contributor
timestamp: January 05, 2025, 10:48:14 am
content: 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.

author: fabry891
author_rank: Newbie
timestamp: January 06, 2025, 05:09:17 pm
content: 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

author: pienari
author_rank: Regular Contributor
timestamp: January 07, 2025, 07:54:49 pm
content: Is there a short in mainboard?

author: fabry891
author_rank: Newbie
timestamp: January 07, 2025, 11:17:30 pm
content: Problem solved.I replaced the 7805A and TYN112 with new parts, and the PSU works. Thanks anyway.

author: Swake
author_rank: Frequent Contributor
timestamp: January 08, 2025, 07:16:09 am
content: You were on the right path since the beginning