Author Topic: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's  (Read 829 times)

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Offline fabry891Topic starter

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ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« on: December 26, 2024, 05:19:50 pm »
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
« Last Edit: December 27, 2024, 10:44:15 pm by fabry891 »
 

Offline m k

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #1 on: January 04, 2025, 09:34:33 pm »
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.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline Swake

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #2 on: January 05, 2025, 10:48:14 am »
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.
When it fits stop using the hammer
 

Offline fabry891Topic starter

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #3 on: January 06, 2025, 05:09:17 pm »
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
 

Offline pienari

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #4 on: January 07, 2025, 07:54:49 pm »
Is there a short in mainboard?
 

Offline fabry891Topic starter

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #5 on: January 07, 2025, 11:17:30 pm »
Problem solved.
I replaced the 7805A and TYN112 with new parts, and the PSU works. Thanks anyway.
 

Offline Swake

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Re: ASTEC AA16242 Power Supply for Olivetti 486 PC 90's
« Reply #6 on: January 08, 2025, 07:16:09 am »
You were on the right path since the beginning  :-+
When it fits stop using the hammer
 


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